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  • A novel method of laser surface hardening treatment inducing different thermal processing condition for Thin-sectioned 100Cr6 steel
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-17
    E. Anusha; Adepu Kumar; S.M. Shariff

    Hardness, microstructure and residual stresses induced on the engineered steel surface have a significant effect on the manufacturing process and the life time of the components. In the present work, these are analysed on laser-treated layer obtained on 100Cr6 bearing steel surface involving different thermal processing conditions. Prior to laser surface hardening treatment, the steel was spheroidized and hardened and tempered with resulting microstructure comprising of globular carbides in the matrix of martensite and retained austenite. A 20-mm wide diode laser beam was employed with a fixed peak laser power in both continuous wave and pulsed wave modes. Additionally, the treatment was carried out with an arrangement to induce fluid contact beneath the workpiece to enhance the heat transfer coefficient. Results indicated maximum improvement in hardness (1050–1100 HV) and compressive residual stress (−630 ± 20 MPa) with retention of core properties on treated surface processed with pulsed-wave mode under fluid contact owing to formation of refined microstructure constituting refined globular carbides (alloy nano-carbides) and retained austenite in martensite matrix. The extent of increase in compressive residual stress and treated layer microhardness was found to depend on the extent of martensite refinement and alloy nano-carbides dispersed in the matrix. Sliding wear tests conducted in both unlubricated and lubricated conditions indicated gradual improvement in wear resistance of the treated surface with increase in cooling rate governed by the thermal processing condition employed with conventionally hardened and tempered one being lowest and laser processed with pulsed wave mode under fluid contact being highest. Apparently, the laser treated surface processed with pulsed-wave mode under fluid contact exhibited reduction in friction coefficient with retention of core properties as compared to untreated counterpart.

    更新日期:2020-01-17
  • Influence of co- and counter-propagating light on the phase-mismatch effect in semiconductor optical amplifiers
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-16
    O.M. Kharraz; M.J. Connelly; A.S.M. Supa'at; A.F. Abas; M.T. Alresheedi; M.A. Mahdi

    The phase-mismatch effect, caused by the difference in confinement factor between transverse electric (TE) and transverse magnetic (TM) modes, has not been observed in semiconductor optical amplifiers (SOAs) and is not typically accounted for. In this work, we investigate the characteristics of the phase-mismatch four wave mixing (FWM) effect, which occurs in SOA devices. Our results reveal a sinc-like response in the intensity of co- and counter-FWM conjugates as a function of the detuning shift between interacting beams. It is demonstrated that the coherence lengths between the phase match/mismatch cycles differ between co- and counter-propagating nondegenerate FWM experiments and depend on the amplified TE/TM polarizations of interacting waves aligned with respect to the birefringent axes of SOAs. The coherence lengths between each phase match/mismatch cycle in co-propagation experiments are found to be 1600 and infinite GHz, respectively, compared to 800 and 400 GHz found in counter-propagation experiments.

    更新日期:2020-01-17
  • Effects of Mg content on keyhole behaviour during deep penetration laser welding of Al-Mg alloys
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-16
    Ye Huang; Chen Shen; Xiangru Ji; Fang Li; Yuelong Zhang; Xueming Hua

    This paper concerns the effects of Mg content on keyhole behaviours during the laser welding process of 5754, 5083 and 5A06 Al-Mg alloys. The features of the vapour plume and keyhole area are extracted from high-speed images with image processing methods. The increase of Mg content leads to the increase of hydrodynamic pressure caused by metal evaporation and decrease of surface tension acting on the keyhole wall. The strong metal evaporation and decrease of surface tension help the formation of keyhole, which both result in a large size of keyhole with deep penetration and low frequency of keyhole collapse. However, the impact of metal vapour could be enhanced by the increase of evaporation and the decrease of both surface tension and viscosity, which leads to the frequent generation of swelling at the rear weldpool and poor formation of the weld bead.

    更新日期:2020-01-17
  • Research of intelligent segment-fitting algorithm for increasing the measurement accuracy of quadrant detector in straightness measuring system
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-15
    Cong Zhang; Fajie Duan; Xiao Fu; Wenzheng Liu; Yuhao Su; Xiuming Li

    In this paper, we propose an intelligent segment-fitting algorithm to increase the measurement accuracy of quadrant detector (QD) in straightness measuring system. Add-subtract algorithm and polynomial fitting are usually adopted to acquire the estimate of the spot projected on QD. The accuracy of QD is limited by the nonlinear relationship between the spot position and its estimate. In order to obtain higher accuracy, the polynomial fitting order must be higher with more calculation amounts, so the new algorithm is designed to optimize the nonlinearity. Through the specific method mentioned in the new algorithm, the whole measurement range of QD can be divided into several segments intelligently. And the data in each segment and between adjacent segments can be simply expressed by the third order polynomial fitting and linear interpolation. The experiment results verified that the algorithm could increase the measurement accuracy with good real-time performance. Within the measurement range of ±250 μm, the residual RMSE of the QD using the proposed algorithm, compared with that using the third order polynomial fitting, was reduced more than 80%, and the calculation amount was reduced to about 1/4 of that using the seventh order polynomial fitting.

    更新日期:2020-01-16
  • Phenomenological studies of femtosecond laser ablation on optical thin films for integrated photonics
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-15
    R. Peyton; V. Guarepi; F. Videla; G.A. Torchia

    In this work, we present a well-supported procedure to fabricate ridge optical waveguides onto thin films of PLZT by femtosecond laser ablation. To achieve smooth-guiding structures that guarantee good optical performance we have studied the characteristics of ablation threshold for different kinematic conditions of fs laser machining and we have also explored the different ablation regimens for several fluences reached. Furthermore, we characterized the morphology and roughness of ridge waveguides through a modal analysis of scattering loss for waveguides conducted by single and multiple scans. An innovative phenomenological model that describes the sidewall roughness to process parameters is proposed in this paper. With this approach, it is possible to extend the manufacturing method of smooth-guiding structures to many optical thin films by fs micromachining, so as to create integrated photonics devices that can be addressed to different technological applications.

    更新日期:2020-01-15
  • High-accuracy high-speed unconstrained fringe projection profilometry of 3D measurement
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-15
    Shichao Yang; Gaoxu Wu; Yanxue Wu; Jin Yan; Huifang Luo; Yinnan Zhang; Fei Liu

    Fringe projection profilometry (FPP) has been extensively used to measure three-dimensional (3D) shape in recent years. Generally, high-frequency fringe patterns ensure high accuracy, while fewer patterns mean higher measuring speed in FPP. However, simultaneously meeting the high-frequency and few-patterns without any constraints are still big challenges, because several additional unwrapping patterns are needed to unwrap the high-frequency patterns. We propose a novel high-accuracy high-speed unconstrained method to obtain the 3D shape by projecting only four fringe patterns. The period of the fringe patterns in the proposed method reaches 70. The high frequency ensures the high measuring accuracy. Besides, only one additional pattern is used to unwrap the high-frequency patterns, ensuring the high measuring speed. This method calculates the absolute phase pixel by pixel independently without any pre-work or constraints, which is suitable for complex and isolated objects. The experimental results verify the high-speed and high-accuracy performance of our method.

    更新日期:2020-01-15
  • Sensitivity enhanced microfiber interferometer ammonia gas sensor by using WO3 nanorods coatings
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-13
    Qiqi Wang; Haiwei Fu; Jijun Ding; Chong Yang; Shuai Wang

    Rapid and accurate detection of toxic and harmful gases in the environment is an important means to prevent poisoning and leakage accidents. A tapered microfiber interferometer coated by WO3 nanorods for gas sensing is fabricated by using flame melting biconical taper method. As a coated material for the microfiber interferometer (MFI) ammonia gas sensor, the WO3 nanorods are made by hydrothermal method, and are dripped onto the surface of the sensor. The WO3 nanorods coating on the sensor surface can absorb ammonia molecules and generate charge transfer, which results in the shift of transmission spectrum. The experimental results show that the prepared sensor has high sensitivity and selectivity to ammonia gas. When the ammonia gas concentration is from 0 to 11640 ppm, the spectrum shift of the WO3 nanorods coated sensor is 16.23 nm. The sensor has good repeatability, selectivity and wide application prospects in the monitor of harmful gases.

    更新日期:2020-01-14
  • Effect of Q-Switched Nd:YAG laser on the anodization of 1050 aluminum alloy
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-13
    Wijdan H. Muttlak; Ali Abdulkhaleq Alwahib; Ayad Zwayen Mohammed; Hussain Sayed

    Short pulses from a Nd:YAG laser effectively enhanced the corrosion resistance of aluminum alloy. Laser heat treatment at energies of 450, 550, 650, and 750 mJ was applied prior to anodization of 1050 aluminum alloy at voltages of 5, 10, and 15 V. The pitting corrosion potential of the anodic oxide layer was investigated in a seawater environment by electrochemical tests, and the corrosion behavior of the aluminum alloy samples was analyzed by polarization and cyclic tests to provide vital information on their corrosion resistance. The corrosion current (Icorr) at 15 V was reduced from 175.47 µA/cm2 to 22.97 µA/cm2 and the potential corrosion (Ecorr) was reduced from −573.4 mV to −334.8 mV by laser treatment. The current density in the cyclic test decreased from 203.58 µA/cm2 to 21.29 µA/cm2 with Laser; the potential corrosion (Ecorr) at 15 V also reduced from −591.9 mV to −358.9 mv. The corrosion resistance for best laser energy was improved at 650 and 750 mJ. Results showed that the oxide layer is influenced by laser treatment. The surface morphology of samples treated before and after laser enhancement was studied, and absorption of laser energy could increase the corrosion resistance of the 1050 aluminum alloy surface. The process and conditions adopted in this paper could improve the pitting corrosion resistance of 1050 aluminum alloy.

    更新日期:2020-01-14
  • Assessment machining of micro-channel textures on PCD by laser-induced plasma and ultra-short pulsed laser ablation
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-13
    Youqiang Xing; Kedong Zhang; Peng Huang; Lei Liu; Ze Wu

    Micro-channels are one of the most common surface textures for applications, however, the machining of micro-channels on polycrystalline diamond (PCD) is still facing challenges due to its intrinsic properties of high brittleness and hardness. In this paper, fabrication of micro-channels by laser induced plasma (LIP) and laser ablation directly (LAD) machining methods on PCD surface is experimentally investigated. For comparing the processing capacity, the influence of different laser process parameters (including overlap, power, frequency, scanning speed and the number of passes) on the geometry and material removal rate of micro-channels is assessed. Results show that the process parameters have a significant influence on the formation of micro-channels, and LIP exhibits higher efficiency compared to LAD in the case of the plasma formation with the high overlap and laser power. The micro-channel depth and width produced by LIP increase with the increasing overlap, laser power and number passes, and that reduce with the increasing frequency and scanning speed; the MRR produced by LIP increases with the increasing overlap, laser power and scanning speed, and that reduces with the increasing frequency and number of passes. Meanwhile, LIP reduces the oxidation reaction inside the micro-channels compared to LAD due to the shielding effect of distilled water.

    更新日期:2020-01-14
  • The conversion from a Gaussian-like beam to a flat-top beam in the laser hardening processing using a fiber coupled diode laser source
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-08
    Hongbo Zhu; Xihong Fu; Shengli Fan; Lei Liang; Xingchen Lin; Yongqiang Ning

    In this paper, a laser beam from a fiber coupled diode laser source is converted from a Gaussian-like distribution to a flat-top distribution using a set of homogenization optical system, which makes this diode laser source more favorable for laser hardening. Employing this diode laser source, hardening experiments are performed on 35CrMo metal steel. By optimizing parameters of the hardening processing, at the scanning speed of 1100 mm/min and laser power of 1940 W, a Rockwell hardness of 57 HRC and a hardened depth of 1.6 mm are achieved. Experimental results demonstrate the processing ability of this diode laser source in the industrial laser hardening.

    更新日期:2020-01-09
  • The effect of laser scanning speed on microstructural evolution during direct laser deposition 12CrNi2 alloy steel
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-08
    Yue Zhou; Suiyuan Chen; Xueting Chen; Jing Liang; Changsheng Liu; Mei Wang

    This paper focused on the effect of different laser scanning speed (4 mm/s, 5 mm/s, 6 mm/s and 7 mm/s) on the microstructural evolution of direct laser deposition (DLD) 12CrNi2 alloy steel, and analyzed the relationship between microstructure and performance of DLD-processed samples. The results showed that the microstructure in the middle of as-deposited samples consisted of a large amount of bainite, a small amount of martensite (M) and ferrite (F). With the increase of laser scanning speed, the fraction of ferrite decreased from 55.6% to 14.7%, while that of martensite increased from nearly 0% to 4.9%. Besides, as increasing the laser scanning speed, granular bainite (GB) transformed into lath bainite (LB) due to the increase of cooling rate, and the fraction of LB reached the maximum of 29.9% when the scanning speed was 7 mm/s. In addition, the functions about the relationship between laser scanning speed and phase fractions were fitted in order to provide a theoretical basis for the design of DLD process parameters. EBSD maps of as-deposited samples exhibited anisotropy due to the complex heat flux direction during the multi-layer laser deposition process. With the increase of laser scanning speed, the grain size showed a downward trend from 5.89 µm2 to 3.44 µm2. The sample fabricated at 7 mm/s contained more LB and M, leading to the highest mean microhardness of 355 ± 6 HV0.2. The sample fabricated at 6 mm/s exhibited the best wear resistance due to its optimum combination of hardness and toughness. Because of a large amount of ferrite with optimal toughness, the sample fabricated at 4 mm/s had the best impact toughness of aku = 80 J/cm2.

    更新日期:2020-01-09
  • Microstructure evolution and mechanical properties of laser metal deposition of Invar 36 alloy
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-08
    Hang Li; Bo Chen; Caiwang Tan; Xiaoguo Song; Jicai Feng
    更新日期:2020-01-08
  • Taper biosensor in fiber ring laser cavity for protein detection
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-06
    M. Mansor; M.H. Abu Bakar; M.F. Omar; Y. Mustapha Kamil; N.H. Zainol Abidin; F.H. Mustafa; M.A. Mahdi

    This paper demonstrates the integration of a bio-functionalized tapered fiber sensor in a fiber laser cavity for sensing of biological molecules. Interferometric effect from the taper generated single wavelength lasing output that was spatially measured to detect any changes. The sensing performance of the integrated system was assessed by immersing the biosensor in various concentrations of avidin ranging from 1 to 10 pM at laser threshold (40 mW) and at the maximum pump power of 200 mW. Selectivity of the sensor was ensured by immobilizing biotin on the surface of the tapered region that would act as complementary molecules to avidin. The proposed setup obtained sensitivity values of 0.40 nm/pM and 1.02 nm/pM at pump power of 40 mW and 200 mW, respectively. The integrated system simplifies the sensing output and analysis without compromising the performance of tapered optical fiber-based biosensor.

    更新日期:2020-01-07
  • Numerical analysis for stress fields induced by laser trepanning of square-slotted blind holes with and without ultrasonic assistance
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-07
    Houxiao Wang; Ye Xu; Guoxiang Xu; Wei Zhou; Sukai Zhu; Qinghu Guo

    The numerical simulation on laser trepanning of square-slotted hole and hole array in stainless steel sheets with and without ultrasonic assistance was reported for analyzing the stress fields on the workpieces trepanned. Based on reasonable modification and verification for the established models using corresponding experimental results, the transient and/or residual stress distribution characteristics, which were induced by single hole trepanning and hole array trepanning with and without ultrasonic assistance, were analyzed systematically and numerically using finite element method (FEM) coupled with self-developed subprograms after predicting the transient temperature fields. The influence of ultrasonic assistance on stress reduction was also discussed. It was shown that the distribution characteristics of equivalent von-Mises stress fields on the top surface of laser trepanned workpiece were different from those on its corresponding bottom surface. For laser-trepanned workpieces, the residual stress distribution characteristics predicted after sufficient cooling were different from the corresponding transient stress characteristics simulated without sufficient cooling. As a whole, the ultrasonic assistance resulted in a small change for the distribution trend of the transient/residual stress field predicted, while the influence of ultrasonic-induced softening effect on laser trepanned workpiece was primarily demonstrated by the effective reduction of the stress values.

    更新日期:2020-01-07
  • Design and fabrication of a single metal layer tunable metamaterial absorber in THz range
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-02
    Min Zhong; Xiaoting Jiang; Xuliang Zhu; Jing Zhang; Jinglin Zhong

    The design and development of resonance-tunable and high-absorptivity metamaterial absorbers is a research hotspot. In this paper, a single-band tunable metamaterial absorber based on the strontium titanate (STO) layer is designed and measured. This absorption peak is enhanced from 90% (D=3.2μm) to 99.4% (D=4.2μm) and the resonant frequency point is shifted from 6.2 THz to 5.8 THz, while it is enhanced and shifted to lower frequencies with the structural parameter P reducing. Measured results show that this absorption peak shows only a 2% reduction when the measured temperature is increased from 300 K to 380 K. Synchronous, the resonant frequency point is shifted from 6.2 THz to 7.1 THz. Based on the temperature-dependence of the STO layer, a temperature tunable metamaterial absorber is experimentally verified.

    更新日期:2020-01-04
  • Switchable and tunable multi-wavelength fiber laser based on a core-offset aluminum coated Mach-Zehnder interferometer
    Opt. Laser Technol. (IF 3.319) Pub Date : 2020-01-02
    J.A. Martin-Vela; J.M. Sierra-Hernandez; E. Gallegos-Arellano; J.M. Estudillo-Ayala; M. Bianchetti; D. Jauregui-Vazquez; J.R. Reyes-Ayona; E.C. Silva-Alvarado; R. Rojas-Laguna

    In this work, a switchable and tunable multi-wavelength erbium-doped fiber laser based on a core-offset aluminum coated Mach-Zehnder interferometer (ACMZI) is presented. The ACMZI is fabricated by core-offset fusion splicing a single-mode fiber segment between two lengths of single mode fiber and then by coating it with aluminum using the thermal evaporation technique. The ACMZI is used as a wavelength selective filter in the proposed ring cavity design. Experimental results show that the laser emission can be switched among a single, double, and triple emission lines by carefully adjusting a polarization controller. Furthermore, the laser lines can be tuned by changing the temperature of the ACMZI. The laser can emit in a single-longitudinal mode and has a single-mode suppression ratio of about 55 dB, a linewidth of 0.05 nm and an efficiency slope of 0.29%. Finally, the laser arrangement is compact, robust, and requires a relatively simple fabrication procedure.

    更新日期:2020-01-04
  • Large measurement range and high sensitivity temperature sensor with FBG cascaded Mach-Zehnder interferometer
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-30
    Rui-jie Tong; Yong Zhao; Hai-feng Hu; Ji-feng Qu

    A high sensitivity and wide measurement range temperature sensor with Mach-Zehnder interferometer (MZI) and fiber Bragg grating (FBG) cascaded is proposed and experimentally implemented. The proposed MZI is fabricated by inserting a section of single mode fiber between two sections of single mode fibers with 62 μm core-offset, where the length of the inserted fiber is 300 μm. Polydimethylsiloxane (PDMS), as a kind of thermo-sensitive material, is covered on core-offset region. Meanwhile, FBG is adopted to enlarge the measurement range. Temperature experiment results turn out to be fruitful for improving the performance of sensitivity and measurement range, and the sensitivity of proposed sensor is up to 10.389 nm/°C from 10 °C to 59.4 °C with good linearity. Moreover, the exhaustively comparison with other optical fiber interferometers reveals that the proposed sensor is simple making, miniature size, good reproducibility, high sensitivity and large measurement range, which has tempting commercial prospect.

    更新日期:2019-12-31
  • Evaluation and improvement of model robustness for plastics samples classification by laser-induced breakdown spectroscopy
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-31
    Qianqian Wang; Xutai Cui; Geer Teng; Yu Zhao; Kai Wei

    The robustness of classification models is important in the real-world application of laser-induced breakdown spectroscopy (LIBS). This study using seven well-known chemometric models (ANN, CART, kNN, LDA, PLS-DA, SVM, and SIMCA) to classify LIBS spectral data from four types of typical plastics samples (ABS, Nylon, 3240, and its improved product FR-4). The robustness of these models for data acquired by different excitation sources (85 mJ pulse @ 1064 nm and 44 mJ pulse @ 532 nm) and over time (collected in November 2015, August 2016, December 2016 and September 2018) were evaluated and compared. The training set was constructed with the spectra acquired by 1064 nm wavelength laser excitation in August 2016. The effect introduced by 5 preprocessing methods (autoscaling, mean-centering, normalized by the total area, normalized by the maximum, and standard normal variate (SNV)) on the robustness of the model was investigated. The performance (accuracy and robustness) of different models was compared and analyzed. The results showed that the robustness of ANN, LDA, and PLS-DA model performed well and the ANN model was best. The experimental results demonstrated that the robustness of the model for LIBS spectra could be improved by using a suitable preprocessing method.

    更新日期:2019-12-31
  • High-energy continuously tunable 8–14 μm picosecond coherent radiation generation from BGSe-OPA pumped by 1064 nm laser
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-31
    Feng Yang; Ji-Yong Yao; Yang-Wu Guo; Lei Yuan; Yong Bo; Qin-Jun Peng; Da-Fu Cui; Yi-Cheng Wu; Zu-Yan Xu

    Powerful and compact coherent radiation source with wavelength covering the 8–14 µm mid-Infrared spectral range is crucial for a number of applications. Here we present a compact high energy widely and continuously tunable picosecond (ps) coherent radiation source from an optical parametric amplifier (OPA) in BaGa4Se7 (BGSe) crystal, providing hundreds of microjoule energy across 8–14 μm. The BGSe-OPA was pumped by a ps 1064 nm laser at a pulse repetition rate of 10 Hz. With a maximum pump energy of 14 mJ, the idler energy of >140 µJ over the entire tuning range was achieved. The maximum idler energy was up to 230 µJ at 9.5 µm, corresponding to a pump to idler energy efficiency of 1.6% and a photon conversion efficiency of 14.7%. Moreover, the corresponding phase-matching angles for 8–14 μm generation were measured experimentally by optical parametric generation method. Finally, the nonlinear absorption of BGSe crystal under 1064 nm pumping was investigated for the first time. The conversion efficiency, typical pulse temporal shapes and beam spatial profiles of idler light generation were calculated based on a BGSe-OPA numerical model.

    更新日期:2019-12-31
  • Synthesis and luminescence characteristic of whitlockite-type AgCa10 (PO4)7:RE3+ (RE = Sm, Dy) phosphors
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-30
    Yongchun Hou; Wenbo Chen; Jihong Xia; Bitao Liu; Lingling Peng; Jun Wang; Qinping Qiang

    A series of whitlockite-type AgCa10(PO4)7:RE3+ (RE = Sm, Dy) phosphors were successfully prepared via a high-temperature solid-state reaction method. The phase purity, photoluminescent properties, and thermal stability have been discussed in detail. Under 404 nm excitation, AgCa10(PO4)7:Sm3+ exhibits red emission (604 nm) corresponding to the 4G5/2 → 6H7/2 transition. Under 352 nm excitation, AgCa10(PO4)7:Dy3+ exhibits two emission peaks at 480 and 574 nm correspond to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transition, respectively. The optimal AgCa10(PO4)7:Sm3+ and AgCa10(PO4)7:Dy3+ phosphors show good thermal stability. When the heating temperature reached 423 K, the relative intensity remains 90% and 86% compared to the luminescence intensity at room temperature of 298 K, respectively. Therefore, the above results indicate AgCa10(PO4)7:RE3+ (RE = Sm, Dy) phosphors have potential applications in LEDs and display devices.

    更新日期:2019-12-31
  • 更新日期:2019-12-31
  • Laser diode optical output dependence on junction temperature for high-power laser systems
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-31
    Nathaniel J. Butt; Rory A. Roberts; Soumya S. Patnaik

    Laser diode optical output is studied and modeled. Four major diode parameters (threshold current, slope efficiency, central wavelength of output, and full-width half maximum of output), which are dependent on diode junction temperature, determine the optical output. The physics and equations representative thereof for each parameter are presented and incorporated into a multiphysics model of a high-power laser system (HPLS) to study the optical power/thermal interactions. Simulations are compared to show how optical power output of an HPLS changes when the temperature dependence of parameters are and are not accounted for in the model. The decrease in laser light intensity out of the HPLS as junction temperature changes is also studied. Intensity is sometimes a more important consideration than optical power because for most applications, laser light is only effective when the output power is focused over a very narrow wavelength range. The research provides higher fidelity diode modeling for effectively understanding optical/thermal interactions and the price to be paid for improper diode thermal management. The research supports our main goal of more accurately representing the thermal loads from the individual components of an HPLS.

    更新日期:2019-12-31
  • Experimental study on the fabrication profile and mechanical properties by substrate-inclined angle using laser melting deposition (LMD) integrating with the substrate of stainless steel
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-31
    Yu He; Jiacheng Wei; Junyan Liu; Xinjian Wang; Yang Wang; Lin He

    At present, almost all the application of laser melting deposition (LMD) additive manufacturing (AM) are based on horizontal substrate plane, which has greatly limited its extensive application in the field of refabrication (RF) or hybrid manufacturing (HM) in the situation of the substrate plane is inclined. This paper reports on the effect of process parameters and substrate-inclined angle on the fabrication profile of LMD, and mechanical properties of stainless steel part fabricated by HM which combined LMD and subtractive manufacturing (SM) inclined substrate were investigated. The experimental results show that the height and displacement offset of deposition layer are on an upward trend along with the increase of laser power and powder feed rate, and on a downward trend along with scanning speed increase. The increase of substrate-inclined angle results in a slight decrease of deposition height and an increase of displacement offset. The standard tensile and bending samples were fabricated by LMD integrating with substrate of stainless steel, and the mechanical performances experimental results indicate that the tensile strength of interface between substrate and LMD part is higher than the LMD fabrication component, both the tensile and yield strength are obviously enhanced by heat treatment, and they reach up to 653 MPa and 456 MPa, respectively. Subsequently, the interface of LMD and substrate part shows a good bending property, and no fracturing process occurs on the interface regardless of the heat treatment. The substrate-inclined angle has almost no effects on the tensile and bending strengths.

    更新日期:2019-12-31
  • Efficient continuous-wave and passively Q-switched lasers based on disordered Nd:Ca0.7La0.3Al12O19 crystals
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-28
    Mengyu Zong; Zhongmian Zhang; Xiaoyue Feng; Mengfei Zhao; Jie Liu; Xiaodong Xu

    A new neodymium-doped (Nd3+-doped) Ca0.7La0.3Al12O19 (Nd:CLA) disordered crystal was successfully grown by the Czochralski method. The performance of diode-pumped Nd:CLA (a-cut and c-cut) lasers was demonstrated for the first time. For the c-cut crystal continuous-wave (CW) operation, we obtained the highest output power of 2.08 W at the wavelength of 1053.2 nm, and the slope efficiency was 23% versus the incident pump power. By inserting a Cr4+:YAG absorber, we successfully achieved a passively Q-switched laser, and the shortest pulse width was 18.36 ns with a peak power of 364.6 W. Compared with a-cut crystal, c-cut crystal has superior laser characteristics.

    更新日期:2019-12-29
  • Laser micromachining of titanium alloy in water and ice at different temperatures
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-27
    Taweeporn Wuttisarn; Viboon Tangwarodomnukun; Chaiya Dumkum

    A clean cut surface with less thermal damage is typically desired in laser micromachining process. Many kinds of cooling substances can be employed to assist the laser ablation for limiting the thermal damage in workpiece and also gaining a higher material removal rate. This paper presents and compares the water- and ice-assisted laser ablation of titanium alloy, in which the effects of water/ice temperature, laser traverse speed and number of laser passes on morphology and dimensions of laser-ablated surface were experimentally investigated. A parametric model for the laser beam refraction at air-water/ice and water-gas bubble interfaces was also developed to determine the refracted distance at the workpiece surface under the different incident angles and water/ice layer thicknesses. The results revealed that the laser ablation in water can produce a clean groove on the metal surface, while only recast and spatters of titanium oxides were found on the laser-scanned track when processing in ice. A remarkable groove can be obtained by using high water temperature together with slow laser traverse speed and more numbers of laser passes. However, the laser beam scattering in water was more apparent than in ice due to water wave, the high refractive index of water and the formation of gas bubbles during the ablation. The findings presented in this study could provide a better understanding of the water- and ice-assisted laser ablation as well as their capability for damage-free fabrication of micro-/submicro-devices.

    更新日期:2019-12-29
  • Optimal design for dual laser beam butt welding process parameter using artificial neural networks and genetic algorithm for SUS316L austenitic stainless steel
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-28
    Bowen Liu; Wentao Jin; Anjin Lu; Kai Liu; Chunming Wang; Gaoyang Mi

    Gas porosity is very critical factor to affect the welding performance and mechanical properties of weld bead. Dual laser beam welding, as a new laser welding process, is helpful to reduce the porosity number in weld bead because of several advantages like enlarging the molten pool, increasing the fluid speed, stabling the keyhole geometry. However, dual laser beam welding requires consideration of more parameters (beam spacing, energy distribution ratio) than single laser beam welding. To optimize dual beam welding process, a 16 groups Taguchi approach together with artificial neural networks (ANN) and genetic algorithm (GA) has been applied to obtain the best welding parameters of laser beam welding for 316L austenite stainless steel during dual beam laser beam welding. X-ray detection results are regarded as the basis for evaluation of porosity number and welding quality. After optimizing, the porosity number is significantly decreased compared to original weld bead. The comparison of microstructure, and yield strength between original parameters and optimized one is carried out to verify optimal results.

    更新日期:2019-12-29
  • 更新日期:2019-12-29
  • An intensity-modulated and large bandwidth magnetic field sensor based on a tapered fiber Bragg grating
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-27
    Pengfei Li; Haitao Yan; Zhanwu Xie; Yanfei Li; Xiaoyan Zhao

    An intensity-modulated and large bandwidth magnetic field fiber sensor with tapered fiber Bragg grating (TFBG) had been proposed and demonstrated by experiments. Fiber Bragg grating (FBG) was created into a tapered fiber to form TFBG, which not only had powerful evanescent field but also possessed large bandwidth for the fiber refractive index decreased along the tapered region. The TFBG inserted into a 0.3 mm diameter glass tube which was filled with the magnetic-fluid (MF), and then this structure was packaged to form an integration magnetic-field fiber sensor. The refractive index of the MF will changed under varied magnetic-field, so the reflection spectral of the sensor should have a corresponding changed with the magnetic-field changed due to the tunable refractive index of MF. We designed the experiments and tested the sensor. The experimental results show that a nonlinear curve is between light intensity variation and changed MF intensity variation, the uniformity fitting degrees are 0.999 and 0.996 among the magnetic field increased and declined and the maximum sensitivity is −0.1933 dB/Oe and −0.1533 dB/Oe, respectively. Moreover, we find magnetic hysteresis has no obvious affection on the magnetic vectors (0 and 180 deg). This proposed magnetic-field sensor has the benefits of no direction disturbance, large bandwidth, high sensitivity, and integration.

    更新日期:2019-12-27
  • Complete confinement and extraordinary propagation of Dyakonov-like polaritons in hBN
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-27
    Shufang Fu; Sheng Zhou; Qiang Zhang; Xuanzhang Wang

    Two Dyakonov-like polaritons (DLPs) were found in the hexagonal boron nitride (hBN). DLP-I lies in the lower reststrahlen band (RB-I) where the hBN is a hyperbolic material, but DLP-II exists in a narrower frequency region where the hBN is an elliptical material, adjacent to the higher reststrahlen band (RB-II). After uniformly considering the DLP electromagnetic fields on the two sides of the hBN surface, we found that the two DLPs are highly confined in the hBN, and even are completely confined in a certain wave-vector. And also, the Poynting vector of either DLP in the hBN seriously deviates from its wave vector and the directional difference outside and inside the hBN dramatically changes with the distance from the surface. The above extraordinary results can support some potential applications in the mid-infrared range, such as high-efficient energy conduction, strictly manipulating infrared-ray direction and infrared-filtering as well as continuous light-splittingfrom micro-meter to nano-meter dimensions.

    更新日期:2019-12-27
  • Adjust dilution level to suppress the precipitated phase by dilution level model of dissimilar metal laser welding with filler wire
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-27
    Bo Cheng; Dongjiang Wu; Jun Liu; Qiang Cui; Siyu Zhou; Guangyi Ma; Fangyong Niu

    To suppress the precipitated phase by adjusting the dilution level of 304 in the dissimilar metal (Hastelloy C-276/SUS 304) laser welding with filler wire, a mathematical model was established between laser parameters and the dilution level of 304 through energy conservation and mass conservation. And the model was verified by the corresponding experiment. The dilution level of 304 is linear with the single pulse energy E and inverse of wire feeding speed (1/VF), and it is also affected by energy melting efficiency and the ratio of two base metals melting. The dilution level of 304 is positively correlated with energy melting efficiency and negatively correlated with the ratio of two base metals melting. Defocusing distance and pulse width can affect dilution level of 304 by changing energy melting efficiency. Welding speed and laser beam offset can affect dilution level of 304 by changing the ratio of two base metals melting. At the same time, the influencing mechanism of the dilution level of 304 on the precipitated phase is revealed. The precipitated phase is directly related to the dilution level of 304. With the increase of dilution level of 304, the volume fraction of precipitated phase increases first and then decreases. When the dilution level of 304 is 24.0% ~ 35.2%, the volume fraction of precipitated phase is the biggest. And when the dilution level of 304 arrives to about 73.0%, the precipitated phase approximately disappears. As the result, the dilution level of 304 can be adjusted to suppress the precipitated phase by the dilution model in the laser welding Hastelloy C-276/SUS 304 with filler wire.

    更新日期:2019-12-27
  • Optical design of a new folding scanning system in MEMS-based lidar
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-26
    Xiaobao Lee; Chunhui Wang; Zhaoxu Luo; Shengqing Li

    In order to solve the two disadvantages, serious divergence and limited scanning angle, of the traditional optical angle expansion in MEMS-based scanning system, a new method is proposed, i.e. an f-theta lens group and a wide-angle lens group are added into the traditional one. Principle of the optical angle expansion is discussed, while the relationship between emergent angle and incident angles has been given. Employing the optical design software ZEMAX, a folding scanning optical system based on MEMS mirror is designed thereafter. The folding scanning optical system we designed can not only scan in a large angle field, which is greater than 60°, but also obtain small spot size at distance of about 160 m, where the spot size is less than 10 cm. This folding scanning optical system has a significant application value in 3D imaging lidar system.

    更新日期:2019-12-27
  • Effect of energy density on laser powder bed fusion built single tracks and thin wall structures with 100 µm preplaced powder layer thickness
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-26
    S.K. Nayak; S.K. Mishra; C.P. Paul; A.N. Jinoop; K.S. Bindra

    Laser Powder Bed Fusion (LPBF) is one of the advanced manufacturing technologies used for fabricating near net shaped components directly from CAD model data by selectively melting pre-placed layer of powder in layer by layer fashion. LPBF process is widely researched with layer thickness up to 60 µm and is now commercially deployed for many metallic materials. However, very limited literature is available in public domain for LPBF with layer thickness >60 µm as the process in this window has many challenges in geometry control and reproducibility due to inherent process instability. However, higher layer thickness with larger beam diameter can bring better productivity and shorter built time with limited compromise on minimum feature size. The present work focuses on a systematic parametric study on single track and thin wall fabrication using LPBF at layer thickness of 100 µm by varying laser power (150–450 W) and scan speed (0.02–0.08 m/s) using SS 316L powder. For the range of parameters under investigation, process window yielding stable tracks (regular and uniform) is obtained for energy density between 87.5 and 140 J/mm3. An analytical model for predicting the width of the track and a regression model for the depth of re-melted zone in the substrate subsurface and track area during single track fabrication is developed in terms of energy density. The average difference in predicted and experimental values for width and area of the track are 3.18% and 7.61%, respectively within the process window. Width of thin walls built at the same parameters is measured and the variation between width of thin wall and track is estimated in terms of energy density. The width of thin walls fabricated are observed to be larger than that of single track built at the same combinations of process parameters primarily due to preheating effect. For the range of parameters under investigation, the highest values of width of thin wall and its difference from corresponding width of track is observed at 112.5 J/mm3 in the process window. The study paves a way in understanding the effect of higher layer thickness on the geometry of LPBF built components.

    更新日期:2019-12-27
  • Temperature tunable lasers with disordered Nd:ABC3O7 crystals
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-26
    Yuanyuan Zhang; Jueru Li; Yanyan Hu; Huadi Zhang; Chengcheng Qiu; Cong Zhang; Xuping Wang; Bing Liu; Yuguo Yang; Xianshun Lv

    We present the continuous-wave (CW) and passively Q-switched laser operation of disordered Nd:ABC3O7 crystals including Nd:SrLaGa3O7, Nd:SrGdGa3O7, and Nd:BaLaGa3O7. Among the Nd:ABC3O7 group members, Nd:SrLaGa3O7 exhibits superior laser properties. A maximum output power reaches 3.88 W under an absorbed pump power of 29.01 W, which is the highest CW output power using LD as the pump source for Nd:SrLaGa3O7 gain medium. Using a Cr4+:YAG crystal as a saturable absorber, the LD pumped passively Q-switched laser is also realized. With Nd:SrLaGa3O7, the shortest pulse width, the largest pulse energy, and the highest peak power are observed to be 10.6 ns, 60.3 μJ, and 5.3 kW, respectively. In the CW laser operation, wavelength tunings are also reported. The center wavelength of this Nd: SrGdGa3O7 laser shifts from 1062.48 to 1063.91 nm by changing the temperature from 60 °C to 135 °C.

    更新日期:2019-12-27
  • 93 fs pulses at watt-level powers from a diode pumped Yb:CaGdAlO4 laser
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-26
    Xianghao Meng; Chong Lv; Baozhen Zhao; Xiaofeng Xi; Qiushi Liu; Xiaohua Zhang; Yuchen Li

    We investigated the performance of diode pumped mode-locked Yb:CGA laser operating in the net normal or net anomalous dispersion region. With 26 W pump power, stable femtosecond laser pulses with average power of 4.5 W are obtained, yielding a pump power slope efficiency of 17%. Operating at 80.5 MHz repetition rate, the laser delivers as short as 93 fs pulse duration with average output power of 4.5 W, corresponding to a pulse energy of 56 nJ and a peak power of 0.59 MW. The oscillator exhibits a passive rms power stability of ~0.38% rms over 5 h in high beam quality.

    更新日期:2019-12-27
  • Development of an adjustable-focus ferrogel mirror
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-26
    Mojtaba Falahati; Wenchen Zhou; Allen Yi; Lei Li

    This paper introduces a low-cost adjustable-focus ferrogel mirror developed by incorporating magnetic nanoparticles into the micellar structure of poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a block-selective solvent. This ferrogel remains homogeneous on exposure to different external magnetic fields. A homebuilt Shack-Hartmann wavefront sensor (SHS) was used to measure and reconstruct the wavefronts and to find the profiles of the deformed ferrogel mirrors under the influence of a magnetic field. The effects of main parameters such as ferrogel composition, magnetic nanoparticles concentration, and magnetic field intensity on the mirror performance were investigated. Ferrogel with a lower solvent loading has a higher Young’s modulus and demonstrates a milder curvature in a given magnetic field. Higher concentration of nanoparticles results in smaller focal lengths of the ferrogel mirror. This deformable mirror has a good optical surface finish and has the potential to be used in adjustable optical systems.

    更新日期:2019-12-27
  • Effect of Ni foil thickness on the microstructure of fusion zone during PHS laser welding
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-24
    Xiaonan Wang; Zhenghui Zhang; Zengrong Hu; Qian Sun; Hongshuang Di; Fan Lv; Lining Sun

    In this present, hot-rolled Al-Si coated press hardened steel (PHS) with 1.5 mm thick was laser tailor welded using Ni foil as an interlayer. The effect of Ni foil thickness on the microstructure evolution of fusion zone (FZ) was studied. With the Ni foil thickness increased, Al had a uniform profile in the FZ but Ni had a segregation in the fusion boundary. JMatPro analysis results showed that the fraction of δ-ferrite at high temperature was decreasing and the primary solidification phase was changed from δ-ferrite to γ phase. The fusion boundary and FZ center had the similar solidification phase evolution during laser welding. The microstructure was the composition of δ-ferrite and lath martensite when the Ni foil was 30 μm, but it was full martensite with the Ni foil increased to 60 μm. Austenite was present in the fusion boundary with the Ni foil increased to 100 μm but it was still lath martensite in FZ center.

    更新日期:2019-12-25
  • Ultra-fine bimodal (α + β) microstructure induced mechanical strength and corrosion resistance of Ti-6Al-4V alloy produced via laser powder bed fusion process
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-24
    B. Pazhanivel; P. Sathiya; G. Sozhan

    The Ti-6Al-4V samples have been fabricated by the laser powder bed fusion (LPBF) process, in which the special emphasis is given on the optimization of laser power and scan speed to attain better mechanical strength and corrosion resistance. In the present study, the percentage elongation was recorded using extensometer and the sample recorded with higher elongation and tensile strength are subjected to corrosion resistance studies and the results are correlated with the microstructural features. The grain refinement occurs during the heat treatment process, the fine grain distribution less than 10 µm results in improved tensile strength and reasonable value of percentage elongation as per the Hall – Petch effect. The finer grain has resulted in improved corrosion resistance and tensile strength which is scarcely reported. The results reveal that as printed Ti-6Al-4V samples contain both the α and β phases in more or less equal percentages. The grain sizes of both α and β phases appear larger in as printed samples, whereas ultra-fine for heat-treated Ti-6Al-4V samples. The formation of ultra-fine grains is due to the dissolution and recrystallization of α and β phases. The corrosion studies in both NaCl and phosphate buffer electrolytes reveal that non-heat treated Ti-6Al-4V samples undergo high corrosion rates, while the heat-treated Ti-6Al-4V samples demonstrate lower corrosion rates. The electrochemical impedance results also reflect a similar trend, where the low corrosion rates were attained due to the formation and buffer layer effect induced by ultra-fine grain structures of β colonies. To highlight, this work paves a new pathway for producing the Ti-6Al-4V alloy samples with high ductility and corrosion resistance through the variations in process parameters and heat treatment conditions.

    更新日期:2019-12-25
  • Benefits of interfacial regulation with interlayers in laser welding Ti6Al4V/316L steel
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-19
    Junzhao Li; Yibo Liu; Yifan Gao; Peng Jin; Qingjie Sun; Jicai Feng
    更新日期:2019-12-20
  • Numerical simulation and experimental investigation of the influence of process parameters on gas-powder flow in laser metal deposition
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-20
    Jiali Gao; Chengzu Wu; Xudong Liang; Yunbo Hao; Kai Zhao

    Uniform, stable and highly converged powder feeding is crucial to guarantee the compact structure, uniform composition and smooth surface of parts in laser metal deposition. Numerical gas-powder flow model for four-stream nozzle was established on the basis of Euler-Lagrange theory. Employing the gas-powder flow model, flow distributions for TC4 and 304L metal powder feeding were obtained respectively in FLUENT. The consistency of simulation and experimental results proved the validity and reliability of the model. Accordingly, influence of powder flow rate, particle properties (particle size, density, sphericity) and other processing parameters on powder flow concentration was studied through numerical simulations and experiments. It was found that metal powder could be transported efficiently with a powder flow rate ranging from 2.5–3.5 kg/h and a carrier gas flow rate of 6 L/min. With the optimized parameters, powder utilization could be improved while the focal length was increased. With the increase of particle size and its shape factor, the concentration of powder flow was increased and focal point was raised. Metal particle sizes of 120 mesh and 100 mesh were found to be suitable for powder utilization. Dispersion of powder flow was controlled more obviously when the shape factor of the particle approached 1.0. And besides, focal position moved up and focal length became shorter with the increase of particle density. Employing the optimized powder flow process parameter for 304L powder with particle size of 75–150 µm, single-track cladding experiment was performed. This study was significant for matching processing parameters with high deposition rate and for further study on nozzle optimization design in laser metal deposition.

    更新日期:2019-12-20
  • Energy scalability of the dissipative soliton in an all-normal-dispersion fiber laser with nonlinear amplifying loop mirror
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-20
    Decai Deng; Haitao Zhang; Qihang Gong; Linlu He; Dan Li; Mali Gong

    We numerically and experimentally report on a high-energy all-normal-dispersion Yb-doped fiber laser with a nonlinear amplifying loop mirror (NALM) acting as the mode-locker. Numerical simulations of the dynamic evolution of dissipative solitons in this structure indicate that the position of gain fiber in the loop mirror plays a key role in promoting pulse energy. Without significant Raman scattering effect, pulse trains with energy and average output power of 22 nJ and 191 mW, respectively, whose duration can be de-chirped to 195 fs, were experimentally obtained from the all-PM-fiber cavity. In addition, the multi-pulsing phenomena at different positions of gain fiber in the loop mirror limits the further increasing of the pulse energy. In this paper, both simulation and experiment are in good qualitative agreement, which provides a method for the mode-locked fiber laser with NALM to control and improve the output properties.

    更新日期:2019-12-20
  • Cancelling lidar echo signal 1/range2 dependence and geometrical form factor shaping by the application of freeform optics
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-20
    Jacek Wojtanowski

    Due to three-dimensionality of the surrounding space, power of the optical echo in laser rangefinders, scanners and variety of lidar systems shows a well-known range−2 dependence. It creates demanding requirements for the receiving electronics in terms of extremely high dynamics of the detected signal. In order to meet these requirements, specific solutions have to be implemented, the side effect of which may be a signal distortion and corresponding precision degradation. In this paper, it is shown, that it is possible to design freeform optical component, which can compensate 1/range2 effect. The aim of this study was to design such a freeform lens which makes laser tele-detection system receiving the same level of optical echo power, no matter of the distance to the target. From simple energy-conservation rules, the required ray mapping for collecting optics can be deduced, which appears however to be non-integrable. To overcome this problem, the modified fully integrable ray mappings were calculated, based on functional minimization method and Monge-Ampere equation, which enabled to obtain smooth freeform refractive surface.

    更新日期:2019-12-20
  • Integral lucky imaging technique for three-dimensional visualization of objects through turbulence
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-19
    Xu Wu; Jiayu Yan; Kenan Wu; Yanan Huang

    Integral lucky imaging method for three-dimensional visualization of objects through turbulence is presented in this work. The method picks images of objects through turbulence with better quality to get a better reconstruction. Numerical experiment was carried out to prove the effectiveness of the proposed method. Analysis as well as simulation results showed that with the decrease of turbulence inner scale, the quality of reconstruction will be reduced. The reconstruction quality can be further improved by using the mass center translation method and the region segmentation method. This paper provides a promising approach for three-dimensional imaging through turbulence.

    更新日期:2019-12-19
  • A high-beam-quality passively Q-switched 2 μm solid-state laser with a WSe2 saturable absorber
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-19
    Linjun Li; Wenchao Cui; Xining Yang; Long Zhou; Yuqiang Yang; Wenqiang Xie; Xiaoming Duan; Yingjie Shen; Jing Han

    In this paper, using the new WSe2 nanosheets as the saturable absorber (SA), a passively Q-switched (PQS) Tm:YAP laser was faultlessly realized. A 1.29-W average output power at 1988.3 nm and a 392.7-ns pulse duration were obtained with a 12.3% optical conversion efficiency, and a 11.3-µJ pulse energy and a 28.9-W peak power were gained with a 12.5-W pump power. In addition, the beam quality factors of Tm:YAP laser in X and Y directions were less than 1.2 under continuous wave (CW) and PQS mode.

    更新日期:2019-12-19
  • Orthogonally polarized dual-wavelength Nd:YVO4/MgO:PPLN intra-cavity frequency doubling green laser
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-19
    Bin Zhang; Qianli Ma; Chang-Qing Xu

    An orthogonally polarized dual-wavelength laser emitting at 542 nm and 543 nm was proposed and demonstrated. The laser was based on a single Nd:YVO4 crystal and two MgO:PPLN crystals. An optical-to-optical (O-O) efficiency as high as 15.3% was achieved when the powers of the two emission wavelengths were equal. The long-term power stability was 4.5% for 542 nm and 3.5% for 543 nm, respectively. The Laser speckle contrast ratio (SCR) was also measured as a function of power ratio of the two emission wavelengths. The measured SCR values agreed with theoretical simulations with a difference less than 5%.

    更新日期:2019-12-19
  • Effects of laser power on the interfacial intermetallic compounds and mechanical properties of dual-spot laser welded–brazed Ti/Al butt joint
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-11
    Peng Li, Zhenglong Lei, Xinrui Zhang, Jinge Liu, Yanbin Chen

    A sound Ti/Al butt joint was successfully obtained by dual-spot laser welding–brazing with a Al-12Si wire as the filler. The influence of laser power on the weld appearance, microstructure of the interfacial intermetallic compounds (IMC), and tensile strength of joints was investigated. With an increase in laser power, the thickness of IMC layer also increased and the morphology of IMC layer changed from a cellular-shape to a serrated-shape, and finally to a club-shape. The microstructure of the interface IMC comprised a brazed zone in which Ti(Al, Si)3 was dominant and the microstructure at the Ti/Ti(Al, Si)3 interface was composed of nano-sized granular Ti5Si3, and Ti7Al5Si12. The highest tensile strength of the joints could reach up 75% of that of the Al base metal. The inhomogeneous IMC layer at the brazing interface caused a decrease in the tensile strength of joints and induced a deflection of fracture path during the tensile process.

    更新日期:2019-12-11
  • Indoor illumination imitating optical parameters of sunny summer daylight
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Jan Vitasek, Tomas Stratil, Jan Latal, Jakub Kolar, Zdenek Wilcek
    更新日期:2019-12-11
  • Measurement of nitric oxide from cigarette burning using TDLAS based on quantum cascade laser
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Fei Zheng, Xuanbing Qiu, Ligang Shao, Shiling Feng, Tong Cheng, Xiaohu He, Qiusheng He, Chuanliang Li, Ruifeng Kan, Christa Fittschen

    Nitric oxide (NO) is an important product released by cigarette burning with significantly negative effects to both environment and human health, but it is hard to be measured in-situ in the process of burning. In this paper, we report a tunable diode laser absorption spectroscopy (TDLAS) set-up using a quantum cascade laser emitting at 5.24 μm to continuously determine the emitted NO mass in cigarette smoke during burning. Wavelength modulation spectroscopy was applied to improve the detection sensitivity and robustness of the measurement system. A simple single-pass gas cell with a volume of 28 cm3 was used to record the absorption spectra, and then the mass of NO was derived based on the measured line strength. Allan variance analysis demonstrated that the limit of detection of system reached 28 ppb over 180 s integration time. Due to the low effective volume, the rise time and the fall time were rapid with 3 s and 6 s, respectively. An adaptive Kalman filter was used to reduce the noise on the concentration measurement. As a result, the measurement precision is improved by a factor of 4.5. For accurate determination the total NO mass, the emissions of mainstream (MS) and sidestream (SS) of a burning cigarette were individually measured at the same continuous flow rate. The recorded results of three types of cigarettes revealed that the NO mass emitted in the MS is correlated with the sampling flow rate, while the NO mass emitted by the same cigarette in the SS is hardly influenced by at different smoke flow rates. And different cigarette types with identical physical dimensions emit approximately equivalent mass of NO. This work provides a promising method for determining the mass of emitted NO and other compositions of cigarettes smoke.

    更新日期:2019-12-11
  • Distributed fiber optic vibration sensing with wide dynamic range, high frequency response, and multi-points accurate location
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Pengfei Ma, Zhenshi Sun, Kun Liu, Junfeng Jiang, Shuang Wang, Liwang Zhang, Lingfeng Weng, Zhongyuan Xu, Tiegen Liu

    An integrated vibration measurement scheme with wide dynamic range, high frequency response and multi-points accurate location is proposed by combining unidirectional Mach-Zehnder interferometer (MZI) and phase sensitive optical time domain reflectometer (φ-OTDR). Using a wavelength division multiplexing (WDM) scheme, the φ-OTDR and the MZI are merged together into one novel system successfully. An improved 3 × 3 coupler-based demodulation method is proposed to demodulate the interference signal produced by the MZI. The vibration frequency is obtained by analyzing the demodulated phase difference. Meanwhile, the vibration position is obtained by analyzing the backscattering signals produced by the φ-OTDR. Experimental results demonstrate that the spatial resolution is 20 m at the sensing length of 4 km and the frequency response reaches up to 10 MHz. Compared with the previous merged systems, this system detects the frequency without dead zone. The MZI part does not affect the φ-OTDR part. The vibration frequency can be obtained accurately with no limitations of π radians phase difference jumps, which means the detectable dynamic range is expanded.

    更新日期:2019-12-11
  • Machine learning-based screening of red blood cells using quantitative phase imaging with micro-spectrocolorimetry
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Veena Singh, Vishal Srivastava, Dalip S. Mehta

    We report simultaneous micro-spectrocolorimetry and quantitative phase imaging (QPI) of human red blood cells (RBCs) using white light interference microscopy. To understand the mechanism of disease at the cellular level and to increase the diagnostic performance of QPI, we integrated it with micro-spectrocolorimetry. Color-coordinates of various spatial locations of RBCs along with 3D phase-maps help to quantify different biophysical parameters. Features extracted from this multimodal technique combined with support vector machine achieved average specificity, sensitivity, and accuracy of 95.52%, 95.58%, and 95.55%, respectively with testing data in classification of healthy and unhealthy RBCs. A better result is obtained by using synergies amongst data as compared to QPI based features only.

    更新日期:2019-12-11
  • Experimental investigations and parametric optimization of laser beam welding of NiTinol sheets by metaheuristic techniques and desirability function analysis
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Susmita Datta, Mohammad Shahid Raza, Amit Kumar Das, Partha Saha, Dilip Kumar Pratihar

    Nitinol is widely used as a functional advanced material in various fields. Poor machinability and lack of available joining techniques are the major drawbacks in the application of NiTinol. The effects of process parameters on the bead geometry, microstructure, new phase formation and mechanical properties in laser welding of one mm thick NiTinol sheet in butt-joint configuration were established through this study. Laser power, scan speed and focal position were considered as input parameters, whereas bead area and microhardness value of the bead were taken as output parameters. Statistical regression analysis was performed in order to establish the input-output relationships. Optimization technique was applied in order to get the minimum bead area satisfying the condition of minimum deviation of microhardness of the bead area from that of the parent material. This was formulated as a constrained optimization problem and solved using three recently developed metaheuristic techniques, namely, Grey Wolf Optimizer (GWO), Cricket Algorithm (CA), Bonobo Optimizer (BO), apart from Genetic algorithm (GA), and Desirability function analysis. A good agreement was found between the results predicted by optimization tools and the experimental results.

    更新日期:2019-12-11
  • Indium tin oxide coated D-shape fiber as saturable absorber for passively Q-switched erbium-doped fiber laser
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    B. Nizamani, A.A.A. Jafry, M.I.M. Abdul Khudus, F.A. Memon, A. Shuhaimi, N. Kasim, E. Hanafi, M. Yasin, S.W. Harun

    We demonstrated a Q-switched Erbium-doped fiber laser (EDFL) using indium-tin-oxide (ITO) deposited onto D-shape fiber as a saturable absorber (SA). The D-shaped fiber was prepared using polishing wheel technique while the ITO was deposited onto the polished surface using electron beam deposition technique to establish excellent evanescent field interaction between the material and light on the surface of the polished region. The SA device was deployed into EDFL ring cavity to generate Q-switched pulses operating at 1566.4 nm. It was able to initiate pulses as short as 2.3 µs with the highest repetition rate of 52.77 kHz. Stability of the SA is proven as it produced stable pulses within the pump power of 55.2–96.4 mW with signal to noise ratio of 58.6 dB. Q-switched EDFL generates pulses with the output power of 300 µW and pulse energy of 5.68 nJ at 96.4 mW pump power. Therefore, ITO deposited onto D-shape fiber can be deployed as SA in EDFL cavity for portable Q-switched laser source.

    更新日期:2019-12-11
  • Radial phased-locked multi-Gaussian Schell-model beam array and its properties in oceanic turbulence
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Dajun Liu, Haiyang Zhong, Guiqiu Wang, Hongming Yin, Yaochuan Wang

    The radial phased-locked multi-Gaussian Schell-model (MGSM) beam array composed by the N MGSM beamlets is first given to describe a new laser array. The evolution properties of radial phased-locked MGSM beam array in free space and oceanic turbulence are discussed in detail. Based on the extended Huygens-Fresnel principle, the MCF and the effective size of radial phased-locked MGSM beam array in oceanic turbulence are derived. The effects of beam parameters and the oceanic turbulence parameters on the spreading and spectral degree of coherence of radial phased-locked MGSM beam array propagating in oceanic turbulence are investigated by using numerical examples. This research may be useful in underwater optical wireless optical communication.

    更新日期:2019-12-11
  • Widely tunable erbium doped fiber ring laser based on loop and double-pass EDFA design
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Serif Ali Sadik, Firat Ertac Durak, Ahmet Altuncu

    This study presents two novel tunable erbium doped fiber ring laser (EDFRL) configurations based on loop EDFA design and double-pass EDFA design, respectively to achieve an ultra-wideband tuning range and stable single-longitudinal-mode lasing operation. A micro-electro-mechanical system (MEMS) based optical tunable band pass filter was utilized as the wavelength selection element. Output spectral and power characteristics of these EDFRLs were experimentally analyzed and discussed. The EDFRLs had moderate and stable output power level (~-3 dBm) over 70 nm tuning range that covers C+L band. Moreover, the proposed EDFRLs could also suppress the undesired multi-longitudinal-modes successfully and have a high (~60 dB) OSNR level in whole tuning range.

    更新日期:2019-12-11
  • Omnidirectional broadband absorber for visible light based on a modulated plasmonic multistack grating
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Igor Leonardo Gomes de Souza, Vitaly Felix Rodriguez-Esquerre

    We present an ultra-thin film absorber made of a metallic/dielectric (Ni/SiO2) metamaterial with a half cylinder cross section. The proposed structure exhibits high absorption for both polarization modes. The total average absorption is over 96% and 92% for transverse electric (TE) and transverse magnetic (TM) polarization, respectively, for normal incidence in all the visible spectrum. This property is well maintained over a wide range of angles of incidence from 0° to 80°. The effects of the structure periodicity are also investigated for both modes and the results show small changes for variations of the order of 200 nm. We also analyzed the structure for a different number of metal-dielectric pairs considering different layers thicknesses. The results show that the absorber can maintain an excellent absorption even with possible errors during the fabrication process. The proposed structure can be used for a wide range of applications, such as thermal emitters, thermophotovoltaics (TPV), optical energy harvesting, thermal detectors among others where a broadband absorption is required.

    更新日期:2019-12-11
  • Passive mode-locking operation of a diode-pumped Tm:YAG laser with a MoS2 saturable absorber
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    Linjun Li, Long Zhou, Tianxin Li, Xining Yang, Wenqiang Xie, Xiaoming Duan, Yingjie Shen, Yuqiang Yang, Wenlong Yang, Han Zhang

    In this paper, we demonstrate the first passive mode-locking operations of a diode-pumped Tm:YAG laser with a MoS2 saturable absorber. In the absence of a MoS2 saturable absorber, the Tm:YAG laser produced a 2.68 W continuous-wave (CW) output power at 2013.8 nm. Under passive mode-locking regime, a maximum average output power of 0.2 W at a pulse repetition rate of 232.2 MHz and a pulse width of about 280 ps were achieved in the experiment. In addition, the near-diffraction limited beam qualities of the CW Tm:YAG laser were achieved.

    更新日期:2019-12-11
  • Evolution behavior of ex-situ NbC and properties of Fe-based laser clad coating
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-09
    Ya-bin Cao, Shi-xin Zhi, Hai-bo Qi, Yang Zhang, Cha Qin, Shao-pu Yang

    The NbC-reinforced Fe-based laser clad coatings were obtained by ex-situ processing. The evolution behavior of ex-situ NbC was quantitatively researched and the microhardness and wear resistance of laser clad coatings were also investigated. The results show that the ex-situ NbC added in clad powder can decompose and re-precipitate during the laser clad process, which affects significantly the content and morphology of NbC. After the added NbC particles decompose during the heating process of laser beam, Nb and C atoms are released into the molten pool. However, a part of Nb atoms cannot react with C to form NbC, but dissolve into the coating matrix or form Fe2Nb with Fe atoms, which decreases the content in NbC in clad coating. Moreover, Most of re-precipitated NbC phases belong to eutectic microstructure and exist in coating in the form of network or featherlike structure instead of the original particle shape. As heterogeneous nucleation core, the undecomposed NbC can promote the re-precipitation of new NbC phases. These new NbC can precipitate on the surface of undecomposed NbC particle, and then form the larger block and petaloid NbC phase with core. Both dissolved Nb atom and NbC precipitate can enhance the microhardness and wear resistance of coating, but the promotion role on the wear resistance is more obvious.

    更新日期:2019-12-11
  • Circlet transform in cell and tissue microscopy
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-10
    O. Sarrafzadeh, H. Rabbani, A. Mehri Dehnavi, A. Talebi

    Automatic detection of objects with circular pattern in digital images is an important topic in many fields of research especially in cell imaging. There are many cells in microscopic images that are circular such as Red Blood Cells (RBCs), White Blood Cells, hematopoietic cells and different types of parasite eggs. Automatic detecting, recognizing and quantifying of these cells provide rich information to pathologists to improve the study/diagnosis of different diseases. Many previously proposed methods utilize the edge information of a given image to detect circles that are not usually applicable for complex images. Fast Circlet Transform (FCT) is a new atomic representation based on using circular basis functions in different scales and frequencies which provides a novel and practical tool for circle detection and analysis of images with circular objects/patterns such as microscopic images. In this paper, three strategies based on FCT are proposed with the applications of FCT in cell and tissue microscopy as follows: In first application, a strategy is proposed for detecting and counting RBCs in microscopic images of blood smear in which an initial estimation of the number of RBCs is made and conflict circles are then removed to detect final and true RBCs. In second application, an algorithm is proposed to count and localize glomeruli in microscopic images of kidney sections by analyzing FCT coefficients in order to directly find circular objects. In third application, a method based on FCT is proposed to detect parasites in microscopic images with high unwanted impurities by modifying FCT coefficients and reconstructing the images. Our experimental results show the effectiveness and better performance of the proposed circlet-based methodologies in microscopic image analysis.

    更新日期:2019-12-11
  • Phase-shifted gratings fabricated with femtosecond laser by overlapped two types of fiber Bragg gratings
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-09
    Xiaoyan Sun, Li Zeng, Haifeng Du, Xinran Dong, Zikun Chang, Youwang Hu, Ji'an Duan

    A phase-shifted fiber Bragg grating (PS-FBG) fabricated by femtosecond laser phase mask technique is demonstrated. The PS-FBG fabricated by overlapped two types of fiber Bragg gratings (FBGs), which is a normal FBG and a titled fiber Bragg grating (TFBG). They are inscribed one over the other on the same section in a single-mode fiber. We researched the effect of different tilt angles to the Bragg wavelength of TFBG. The intensity and wavelength of PS-FBGs can be changed by controlling tilt angles. The method has advantages of simple and efficient fabrication as well as high-quality spectrum. Meanwhile it has a good repeatability. Additionally, the strain and temperature sensitivities of the 0° + 3° PS-FBG are experimentally measured, which are 0.867 pm/με and 14.91 pm/℃, respectively.

    更新日期:2019-12-09
  • Biocompatible nano-ripples structured surfaces induced by femtosecond laser to rebel bacterial colonization and biofilm formation
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-06
    Xiao Luo, Shenglian Yao, Hongjun Zhang, Mingyong Cai, Weijian Liu, Rui Pan, Changhao Chen, Xiumei Wang, Luning Wang, Minlin Zhong
    更新日期:2019-12-07
  • Ultra-broadband and wide-angle absorption based on 3D-printed pyramid
    Opt. Laser Technol. (IF 3.319) Pub Date : 2019-12-06
    Xiqiao Chen, Zhuang Wu, Zilong Zhang, Yanhong Zou

    This paper proposes a 3D-printed pyramidal absorber, which comprises of the printing filaments, carbon-loaded Acrylonitrile Butadiene Styrene (ABS). This ABS has certain absorption effects, and shows simple and rapid prototyping characteristics. Here, we experimentally demonstrated the directly printed pyramidal absorber showing the absorption more than 90% within the frequency range from 5.3 to 18 GHz. The incident energy at the low and high peak frequencies are mostly attenuated by λ/4 resonances, corresponding to the wavelength of λ/4 and 3λ/4 separately. Distinct from the flat absorber, the pyramidal structure and absorbent take synergistic effects for broadband absorption. Additionally, the pyramid maintained its absorption bandwidth within quite a wide incident angle, 50° for transverse electric (TE) polarization and 60° for transverse magnetic (TM) polarization. It is expected that the proposed pyramidal absorber has great potential for application in radar cross section reduction and electromagnetic shielding.

    更新日期:2019-12-06
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