The improvement potential of ultrafast all-optical switching by soliton self-trapping, using all-solid dual-core fibres with high index contrast, was analyzed numerically. The study of the femtosecond nonlinear propagation was performed based on coupled generalised nonlinear Schrödinger equations considering three fibre architectures: homogeneous cladding all-solid, photonic crystal air-glass, and photonic crystal all-solid. The structural geometries of all three architectures were optimised in order to support high-contrast switching performance in the C-band, considering pulse widths at the 100 fs level. Comparing the three structural alternatives, the lowest switching energies at common excitation parameters (1700 nm and 70 fs pulses) were predicted for the homogeneous cladding dual-core structure. Further optimization of the excitation wavelength and pulse width resulted in lower switching energies and simultaneous improvement of the switching contrasts at the combination of...

The guiding of a 6 GHz electromagnetic (EM) wave along a plasma filament produced by intense femtosecond laser pulses is investigated with the electromagnetic simulation software XFDTD. The results confirm that the plasma filament can guide the EM wave over a long distance, with low attenuation relative to freely propagating the signal. Furthermore, the filament can change the phase wavelength of the signal in the waveguide. Also notable is that the power density of the wave along the filament monotonically decreases with increasing EM wave propagation length. The wavelength of the EM wave along the plasma filament is about 4.98 cm, which is slightly less than that of the incident 6 GHz signal, i.e., the wave velocity along the filament is less than the speed of light.

The spectroscopic and laser properties of mixed fluoride Tm:CaF 2 –SrF 2 crystals were investigated. The 1.9 ##IMG## [http://ej.iop.org/images/1612-202X/17/2/025802/lplab5f58ieqn001.gif] m radiation was obtained in two samples with Tm 3+ ion doping concentrations of 1.0 mol% and 2.0 mol% under laser diode pumping at 763 nm. The highest slope efficiency of 32.5% and the widest laser tuning range of 232 nm (1761–1993 nm) were demonstrated with the 1%-doped sample. The maximal output power amplitude of 3.4 W at 1902 nm for an absorbed pump power amplitude of 13.8 W was demonstrated with the 2%-doped sample.

A stable single longitudinal mode optofluidic microcavity laser based on an antiresonant hollow-core fiber (AR-HCF) is proposed and experimentally demonstrated. A hexagonal silica ring inside the AR-HCF is used as the resonator of the optofluidic laser. Experimental results show that the laser can operate in a stable single longitudinal mode without optical mode-selection device and only by introducing a micro-fluid control device. With 5 mmol l −1 Rhodamine B as gain medium, the threshold of the single longitudinal mode microcavity laser is 554 nJ mm −2 and the lasing wavelength is 594.3 nm. When the micro-fluid control speed is 1.5 µ l min −1 , the output power fluctuation of the laser is less than 4% within 35 min. By changing the concentration and type of gain medium, the stability of the single longitudinal mode lasing output can be maintained and the lasing wavelength can be regulated. It holds great promising applications in the multiple...

The master equation for the atom-field system with degenerate atomic levels and two polarization modes of the quantized field in a damped micro-cavity is obtained in the basis of eigenvectors of the interaction operator. The solution for the lossless cavity is obtained. The analytic expressions for the probability of emission of the photon in the cavity by an excited atom and of the photon polarization matrix are derived in the ‘strong coupling’ and ‘bad cavity’ approximations for arbitrary values of angular momenta of atomic levels. The dependence of the photon polarization on the polarization of the short excitation pulse is studied.

We demonstrate a tunable solid-state polymer dye laser with quasi-longitudinal pumping by two green ( λ = 513 nm) laser diodes. Tuning curves with a maximum efficiency of 13% were attained, using a plate of crystalline quartz (Lyot filter) for wavelength selection. In a three-mirror cavity with partial compensation of astigmatism, the total tuning range was 62 nm (from 545 nm to 607 nm) for pyrromethene dyes: PM567, PM580 and PM597. The best results were achieved with active elements based on Pyrromethene 580 laser dye in a mixture of polyvinyl butyral or a copolymer of butylmethacrylate and methacrylic acid (ratio 9:1) with the addition of 30% dibutylsebacinate as a plasticizer.

A combined mechano- and chemo-bactericidal nanomorphology, consisting of periodical surface structures on silicon with deposited nanoparticles of selenium, tellurium oxide, antimony oxide and silver, was fabricated via laser ablation in deionized water with femto- and nanosecond laser systems. The resulting functional surfaces were tested against the formation of Staphylococcus aureus biofilms, and their morphology and elemental composition was characterized with scanning electron microscopy and energy-dispersive x-ray and Raman spectroscopy. Antibacterial properties were suggested to originate from the combined chemical toxicity of nanoparticles and the mechanical damage caused by the sharp nanoscale relief on silicon.

We theoretically demonstrate the Fano resonance and the conversion from fast to slow light in a hybrid semiconductor quantum dot (SQDs)-metal nanoparticle (MNPs) with cavity quantum electrodynamics treatment. The absorption spectra of the weak probe field exhibit a series of asymmetric Fano line shapes and their related optical propagation properties, such as fast and slow light effects, are investigated based on the hybrid system for suitable parametric regimes. Further, the transparency windows (i.e. the absorption dip approaches zero) in the probe absorption spectra are accompanied by the rapid steep dispersion of the Fano resonance profile, which promises the slow or fast light effect, and even tunable fast-to-slow light propagation (or vice versa) can be achieved by controlling different parameter regimes. Therefore the investigation may indicate promising applications in quantum information processing based on the hybrid SQD-MNP system.

Based on the nonincreasing property of quantum coherence via skew information under incoherent completely positive and trace-preserving maps, we propose a non-Markovianity measure for open quantum processes. As applications, by applying the proposed measure to some typical noisy channels, we find that it is equivalent to the three previous measures of non-Markovianity for phase damping and amplitude damping channels, i.e. the measures based on the quantum trace distance, dynamical divisibility, and quantum mutual information. For the random unitary channel, it is equivalent to the non-Markovianity measure based on l 1 norm of coherence for a class of output states and it is incompletely equivalent to the measure based on dynamical divisibility. We also use the modified Tsallis relative ##IMG## [http://ej.iop.org/images/1612-202X/17/1/015202/lplab5fe3ieqn001.gif] entropy of coherence to detect the non-Markovianity of dynamics of quantum ...

The optical properties and morphology of laser generated aluminum and copper phthalocyanine nanoparticles (nAlPc and nCuPc) in water are experimentally studied. A near-infrared laser source of nanosecond pulse duration was used for the fragmentation of a Pc micro-powder suspended in H 2 O. The extinction spectra in the visible and near-IR range of nanoparticle colloidal solutions in milli-Q water were acquired by means of optical spectroscopy. The optical density of both nCuPc and nAlPc increases with the laser fragmentation time. Transmission electron microscopy shows that nCuPcs are made of short (100 nm) rectangular bars interconnected at various angles with other bars. A similar morphology is observed for nAlPc.

We report on the demonstration of a symmetrically cooled thin-disk laser concept using Ti:sapphire for the gain medium and plano-convex shaped single crystal diamond as intracavity heat spreaders. This allowed us to increase the absorbed pump intensity by at least a factor of five compared to a previously reported Ti:sapphire thin-disk oscillator.

In this study, laser-induced breakdown spectroscopy (LIBS) was applied to detect some samples of tea, which were picked in three different seasons: spring, summer, and autumn. The relationship between some elements in the tea and the characteristics of its origin was analyzed. By comparing the relative intensity of the characteristic spectral lines of some elements in the tea samples harvested in different seasons, it was found that the content of some elements varies with the seasons. Besides this, the Pb in tea was quantitatively analyzed by the internal standard method. Then, the detection limit of Pb in the tea samples by LIBS in the experiment was calculated to be about 48.4 mg kg −1 . Moreover, the properties of plasma temperature and electron number density were studied and local thermal equilibrium state was verified. The carbon-nitrogen (CN) molecular bands were also clearly observed in the experiment and simulated. The vibrational temperature and rotational te...

We have investigated nonlinear laser ̶ matter interaction inside silicon under tight focusing conditions by continuously tuning driving pulse duration from femtosecond to picosecond timescales. Such tailoring of laser pulse width provides a new route for energy delivery into a microvolume avoiding two-photon absorption and plasma defocusing in the pre-focal region. As a result, we have achieved values of saturated deposited energy density and plasma electron concentration of as high as 1 kJ cm −3 and 10 19 cm −3 respectively, which is lower than the threshold of irreversible structural transformation. For further increase of energy delivery inside silicon, a two-color technique supported by extremely tight focusing can be realized, forming a roadmap to the 3D industrial micromachining of planar bulk silicon.

In this paper, we demonstrate that the intensity difference squeezing (IDS) of parametric amplified four-wave mixing (PA-FWM) can be modulated by the phase-sensitive dressed effect in a hot rubidium (Rb) atomic system. The introduction of phase-sensitive dressed effect can enhance the degree of IDS of PA-FWM to −8.1 dB, as compared to that in the phase-insensitive dressed PA-FWM of −6.6 dB. The phase-sensitive dressing field can not only enhance the degree of IDS of PA-FWM by the dressed effect, but can also be treated as the seed beam of the PA-six wave mixing process. So, double-injected three-mode IDS obviously has a bigger degree of IDS compared with the single-injection case. One advantage of the current scheme for enhancing the generated IDS is that the experimental setup is simple and mechanically stable. These outcomes can be used in the fabrication of quantum devices and the realization of quantum metrology.

Quantum fluctuations of soliton pulses produced via two-soliton fission in the optical dispersion oscillating fiber were investigated using perturbation analysis and back-propagation method. It was shown that in the fiber with periodic dispersion, two-soliton pulses decay to two similar entangled pulses having the same photon numbers of modes and different phases due to shifts of carrier frequencies of the pulses.

Early security proofs of the keys in quantum cryptography systems were based on the assumption that the transmitting and receiving stations were completely isolated from the outside world—the eavesdropper. However, this condition cannot be implemented in practice, since quantum cryptography systems are open systems, in the sense that an eavesdropper can have indirect access, for example, through a fiber communication channel to critical equipment elements (phase modulators, intensity modulators, etc) using active sensing of the state of these elements—Trojan-horse attacks. A new Trojan-horse attack based on joint unambiguous measurements of reflected probing states from an intensity modulator and information states in a quantum communication channel is proposed. Estimates of attack parameters for a number of quantum key distribution protocols are given, when an attack leads to compromise of keys.

Double-clad Er-doped fibers highly doped with aluminum (up to 3 mol.%) and fluorine (up to 1.5 wt.%) have been fabricated and studied. The fibers have a core numerical aperture of approximately 0.055, which allowed us to achieve a single-mode propagation regime for a fiber core diameter of 35 µ m. The possibility of increasing the pump-to-signal conversion efficiency in the L-band using the developed double-clad Er-doped fibers was demonstrated. Utilization of the F–GeO 2 –Al 2 O 3 –SiO 2 –Er fiber together with a P 2 O 5 –Al 2 O 3 –SiO 2 –Er fiber was found to be promising for single-frequency amplifiers because the fibers have negligible overlap of the stimulated Brillouin scattering gain. This feature allowed us to build a cascaded double-clad Er-doped fiber amplifier (two Er-doped fibers of different types were spliced one by one) with a threshold of stimulated Brillouin scattering greater...

In this paper, we demonstrate a high-power, narrow-linewidth, near-diffraction-limited all-fiber laser based on a one-stage high power amplifier configuration. The seed source is a fiber oscillator with a short cavity length in order to suppress the spectral broadening effect, the linewidth is 0.027 nm at the laser power of 7.3 W. Then only one-stage high-power amplifier is used to scale up the seed power. It is found this simple laser structure can obtain an output power of 2.4 kW with a linewidth of 0.24 nm. Meanwhile, the center wavelength only shifts 0.025 nm during the amplification process, which is about 0.1 times of the linewidth. The output laser at maximum power has a near-diffraction-limited beam quality, the M 2 is 1.27 in the x -direction and 1.35 in the y -direction, respectively. Besides, for the first time, we discover the beam fluctuations (different from the mode instability) with a frequency of a few Hz, this new phenomenon limit...

A multichannel metallic dual nano-wall square split-ring resonator is proposed for both filter and sensor applications. It is comprised of four square split-ring resonators which filter out wavelengths at 598 nm, 675 nm, 753 nm and 838 nm that are transmitted through respective ports connected to the rings. The proposed design is flexible, which allows the filtering of any desired wavelengths by varying the geometry of the ring. By incorporating the nano-walls in the ring, it is likely to excite the non-integer modes, which are not possible in regular rings. The transmission spectrum of the filter lies in a near-infrared region, which is a biological transparency window and makes it interesting for photo-thermal therapy applications. Due to its design benefits, this structure can also be used in biosensing applications. The best sensitivity, Q -factor and figure of merit of the sensor is obtained at 793.3 nm/RIU, 82.1 and 52.9, respectively.

We have investigated the teleportation of quantum Fisher information (QFI) for a single-qubit system by using two different maximally entangled pure states as resources influenced by a Davies-type Markovian environment. According to the definition of QFI, we first derive the explicit analytical results of QFI with respect to the weight parameter ##IMG## [http://ej.iop.org/images/1612-202X/16/12/125202/lplab5529ieqn001.gif] and phase parameter ##IMG## [http://ej.iop.org/images/1612-202X/16/12/125202/lplab5529ieqn002.gif] under decoherence. Our analytical results show that the teleportation of QFI is seriously affected by two classes of environment, including dissipative and pure dephasing, depending on the parameter ##IMG## [http://ej.iop.org/images/1612-202X/16/12/125202/lplab5529ieqn003.gif] of the teleported state during the teleportation process. In particular, for ##IMG## [http:...]

The Heisenberg–Langevin equation for a spatial laser soliton in a wide-aperture laser with saturable absorption is constructed within the framework of consistent quantum electrodynamics. We discuss in detail the canonical variables for the generation field and the material two-level medium, consisting of centres providing amplification and absorption. It is assumed that laser generation evolves in time much more slowly than an atomic media. This assumption makes it possible to apply the adiabatic approximation and construct a closed equation for the amplitude of a laser field. Much attention is paid to the formulation of Langevin sources when deriving the equation since they play a decisive role in the formation of solitons’ quantum statistical features. To provide an appropriate procedure for observing the quantum squeezing of a soliton, synchronization of laser generation by an external weak electromagnetic field is considered. Here we also present the results of the analysis ...

A new two-temperature (2- T ) algorithm for an estimation of the temperatures in a non-uniform hot zone by absorption spectrometry with tunable diode lasers (TDLAS) is demonstrated in experiments with the Wolfhard–Parker burner. A laminar premixed flame of the burner has a planar structure with zones of relatively constant temperature and zones with pronounced temperature gradients. The temperature was evaluated by fitting the experimental absorption spectra of a H 2 O molecule by the linear combination of two single temperature spectra simulated using spectroscopic databases. The radiation of the two diode lasers generating in 7185 cm −1 and 7444 cm −1 spectral ranges crossed the flame in the direction along the slots at different heights above the burner. Temperature profiles of the flame obtained by fitting the line-of-sight TDLAS experimental spectra using a 2- T algorithm are compared with the local temperatures measured by coherent a...

The interaction of 3-level atom with two resonant quantum fields is investigated and an analytical solution is obtained. The effect of coherent population trapping and formation of a ‘dark’ state is analyzed. The atomic and field dynamics is found to be very sensitive to the photon statistics and relative phases of the initial quantum field states. The effect of quantum ‘death’ and ‘birth’ of atomic transitions and mean photon number evolution is demonstrated. Strong entanglement between atomic and field subsystems arising during the interaction is found and studied in details.

When a few-cycle vortex laser interacted with an inversion-symmetric atomic-like system, beyond the usual odd-order harmonics, some additional components also occur. The detailed numerical investigation on their transverse field distributions discloses that they depend sensitively on the carrier-envelope-phase (CEP) and the rotation period of the transverse distribution is 2 π . This could be used to directly determine the CEP value of an incident pulse, unique without falling back on specific polar molecules or static electric fields.

We show that thermal noise could play a positive role in generating one-way Einstein–Podolsky–Rosen (EPR) steering of two cavity fields dispersively interacting with a single four-level atom, each of which is independently coupled to a thermal reservoir. In the low- Q and weak Raman transition regimes, two output fields exhibit asymmetric EPR steering and the steering direction could be easily controlled by adjusting the mean photon numbers of the thermal reservoirs and the decay rates of cavities. Striking features are present in our scheme. First, one-way EPR steering is achieved by using the couplings of the cavities with the heat baths, which sheds light on the quantum state manipulation in the presence of decoherence. Second, the obtainable EPR steering occurs between the cavity fields in the low- Q regime, which relaxes the constraints on the use of good cavities and so makes our scheme more practical. Third, the correlation properties of the output modes are c...

Dynamic characterization of self-induced beating sinusoidal wave (BSW) oscillations and related phenomena, which were previously explored in a thin-slice dual-polarization solid-state laser operating in the regime of incomplete mode-locking of orthogonally polarized transverse eigenmodes, namely, a quasi-locked state Otsuka (2018 Laser Phys. Lett . 15 075001), is performed in terms of the amplitude correlation coefficient and intensity circulation among various orthogonally polarized mode pairs. Polarization-dependent symmetry-breaking featuring a nonreciprocal intensity flow for different orthogonally polarized mode pairs operating in the BSW state are found. The singular state is hidden in a nonlinear system where a perfect mode-locked BSW state with a large amplitude correlation coefficient featuring reciprocal intensity flow is established for a transverse mode pair possessing particular polarization directions that are related to the intensity ratio of orthogon...

A permanent-magnet system with a maximum magnetic field exceeding 3 T, which is a record value for Faraday isolators, has been created. The magnitude of the field in the system is close to the theoretical limit that can be achieved at an optimal magnetization distribution. This is possible thanks to the use in the central area of the system of magnetic conductors that possess a saturation induction higher than the residual induction of the strongest magnets and provide more optimal magnetization distribution than magnets. But the main feature of the system is control of demagnetizing fields in the center of the system by optimizing the position and shape of magnetic conductors, thus retaining the maximum volume of the magnets in the core of the system without the risk of their magnetization reversal. The technology of controlling demagnetizing fields by means of magnetic conductors is proven for the first time. The created system is promising for the development of Faraday isola...

Ultrafast laser pulse interaction with a stainless steel surface leading to the formation of self-organized nanostructures is observed. Optical and scanning electron microscopy were used for sample characterization. We also demonstrated that, depending on the type of steel, the antibacterial properties change.

Spontaneous and stimulated Raman scattering are studied in Na 2 W 2 O 7 crystal with an orthorhombic structure. The polarized Raman scattering spectra corresponding to all the six independent Raman tensor components are measured. The frequencies of the registered vibrational modes are identified. The most intense Raman mode is observed at 956.3 cm −1 with a linewidth of 3.5 cm −1 . The first observation of stimulated Raman scattering in Na 2 W 2 O 7 under excitation by the second harmonic of a mode-locked Nd:YLF laser with a pulse duration of 25 ps is reported. Raman gains at a wavelength of 523.5 nm in Na 2 W 2 O 7 and KGd(WO 4 ) 2 crystals are measured. We believe that disodium ditungstate crystal is a promising medium for Raman laser converters.

Enhancing or suppressing the upconversion luminescence (UCL) of rare-earth ions has very important application prospects in various areas such as color display and optoelectronic devices. However, the control efficiency is not always optimal because the pre-designed femtosecond laser field is usually not the most suitable. The femtosecond laser pulse-shaping technique has proved to be a very well-established tool to obtain the UCL enhancement and suppression. In this letter, we experimentally realize the maximum UCL enhancement and suppression of Dy 3+ -doped glass by optimizing the femtosecond laser spectral phase based on a genetic algorithm. Our experimental results show that the UCL intensity can be further enhanced and also completely suppressed. The physical control mechanism of the UCL enhancement and suppression is interpreted based on a resonant-mediated two-photon absorption model and the obtained optimal femtosecond laser spectral phase. This study provides a...

The effective interaction between two classical nonrelativistic electrons (positrons) in the presence of intense electromagnetic radiation (one and two waves) is theoretically studied. Small relativistic corrections are considered in the laboratory reference frame. The field of an intense wave forms the movement of particles in such a way that their trajectories are practically parallel for quite a long time and, in the perpendicular direction, the particles shift slightly, approaching first and then moving away from each other. This result can be considered an effective attraction for same-charged particles. We show that the effective attraction of two electrons and two positrons could be substantially asymmetric.

A method for electronically controlled formation of user-defined laser pulse patterns in a synchronously pumped laser based on a semiconductor optical amplifier and an all-fiber resonator is proposed and investigated. It is demonstrated that synchronous pumping allows mode-locked operation with the laser radiation structured as an arbitrary pulse pattern repeatable on each cavity round trip. Direct electronic control of the structure and shape of the generated laser pulse patterns is implemented. The accuracy of the reproduction of modulation pulse patterns and waveforms delivered from a radiofrequency arbitrary waveform generator is examined. The time constraint on the pulse pattern formation in the steady-state mode-locked lasing regime is revealed, as well as the feasibility of the quasi-steady-state regime with on-the-lasing continuous modification of the pulse pattern structure.

The protective barriers of the CNS present challenges during the treatment and monitoring of diseases. In particular, the blood brain barrier is a major hindrance to the delivery of imaging contrast agents and therapeutics to the brain. In this work, we use gas microbubble-assisted focused ultrasound to transiently open the blood brain barrier and locally deliver silica coated gold nanorods across the barrier. This particular nanoagent possesses a strong optical absorption which enables in vivo and ex vivo visualization of the delivered particles using ultrasound-guided photoacoustic imaging. The results of these studies demonstrate the potential of ultrasound-guided photoacoustics to image contrast agents delivered via microbubble-assisted focused ultrasound for longitudinal diagnostic imaging and for therapeutic monitoring of neurological diseases.

Scattering dominates light propagation in biological tissue, and therefore restricts both resolution and penetration depth in optical imaging within thick tissue. As photons travel into the diffusive regime-typically 1 mm beneath human skin, their trajectories transition from ballistic to diffusive due to increased number of scattering events, which makes it impossible to focus, much less track, photon paths. Consequently, imaging methods that rely on controlled light illumination are ineffective in deep tissue. This problem has recently been addressed by a novel method capable of dynamically focusing light in thick scattering media via time reversal of ultrasonically encoded (TRUE) diffused light. Here, using photorefractive materials as phase conjugate mirrors, we show a direct visualization and dynamic control of optical focusing with this light delivery method, and demonstrate its application for focused fluorescence excitation and imaging in thick turbid media. These abilities are increasingly critical to understanding the dynamic interactions of light with biological matter and processes at different system levels, as well as their applications for biomedical diagnosis and therapy.

In this letter, we, for the first time, report on coherent anti-Stokes Raman scattering (CARS) spectroscopy of an ensemble of silicon nanowires (SiNWs) formed by wet chemical etching of crystalline silicon with a mask of silver nanoparticles. The fabricated SiNWs have diameter ranged from 30 to 200 nm and demonstrate both visible and infrared photolumine cence (PL) and spontaneous Raman signal, with their intensities depending on presence of silver nanoparticles in SiNWs. The efficiency of CARS in SiNW ensembles is found to be significantly higher than that in crystalline silicon. The results of CARS and PL measurements are explained in terms of resonant excitation of the electron states attributed to silicon nanoparticles.

Accurate non-invasive assessment of tissue elasticity in vivo is required for early diagnostics of many tissue abnormalities. We have developed a focused air-pulse system that produces a low-pressure and short-duration air stream, which can be used to excite transient surface waves (SWs) in soft tissues. System characteristics were studied using a high-resolution analog pressure transducer to describe the excitation pressure. Results indicate that the excitation pressure provided by the air-pulse system can be easily controlled by the air source pressure, the angle of delivery, and the distance between the tissue surface and the port of the air-pulse system. Furthermore, we integrated this focused air-pulse system with phase-sensitive optical coherence tomography (PhS-OCT) to make non-contact measurements of tissue elasticity. The PhS-OCT system is used to assess the group velocity of SW propagation, which can be used to determine Young's modulus. Pilot experiments were performed on gelatin phantoms with different concentrations (10%, 12% and 14% w/w). The results demonstrate the feasibility of using this focused air-pulse system combined with PhS-OCT to estimate tissue elasticity. This easily controlled non-contact technique is potentially useful to study the biomechanical properties of ocular and other tissues in vivo.

A method for selectively inducing apoptosis in tumor nodules is presented, with close-to-cellular level resolution, using 3D-resolved widefield temporal focusing illumination. Treatment times on the order of seconds were achieved using Verteporfin as the photosensitizer, with doses of 30 μg ml-1 and below. Results were achieved on both 2D and 3D cell cultures, demonstrating that treatment was possible through approximately one hundred microns of dense tumor nodules.

Erbium doped fiber amplifiers play an important role in various applications, spanning from fiber communication to optical sensing. Unfortunately, their gain bandwidth is limited to telecom C- and L-bands (from 1530–1625 nm). The application of bismuth-doped fibers is a promising approach for optical signal amplification at longer wavelengths. In this paper, a bismuth-doped fiber power amplifier seeded with a 1651 nm single-frequency laser diode is presented and its performance is experimentally analyzed. This amplifier may be used to improve performance of systems for methane detection, e.g. those based on photoacoustic spectroscopy or in remote/stand-off configuration (methane has a molecular absorption line near to 1651 nm). Two configurations of the amplifier are demonstrated and in both cases an output power of more than 80 mW is obtained. Limitations of current design are discussed. The obtained results give good a perspective for simple and compact fiber amplifiers with o...

We report on the comparison of two approaches to the reconstruction of oxygen saturation (StO 2 ) within blood vessels from multispectral optoacoustic (OA) measurements. The spatially-resolving approach is based on determination of the optical absorption coefficient µ a from OA signal amplitudes, while the calibration-free approach is based on evaluation of the effective optical attenuation coefficient µ eff derived from the in-depth OA signal decay. Both approaches were verified in phantom experiments as well as in in vitro and in vivo measurements. The results demonstrate good agreement of µ a spectra derived from OA signal amplitudes with the published data indicating this approach to be preferable for the in vivo determination of StO 2 . Reconstruction of µ a spectra from the in vivo measured OA signal amplitudes in a rat yields StO 2 values of 0.57...

In this paper, we study the effect of different temporal light field patterns on compressive temporal ghost imaging. Wavelength division multiplexing technology is used for temporal ghost imaging to improve imaging efficiency. The applicability, robustness, and reconstruction performance of different temporal light fields are verified on the basis of research on the temporal ghost imaging mechanism. Simulation shows that Hadamard temporal light field pattern has better reconstruction effect and anti-noise ability than other light field patterns, and applies to different kinds of signals.

Laser biological effects are a hot topic in laser medicine. In this study, to explore the quantitative biological effect of laser-induced wound healing and to provide guidance for expanding the clinical application of laser therapy, the injury effects and repair characteristics of skin tissue are studied through infrared laser irradiation of the skin of miniature pigs. Live pig skin was irradiated at multiple spots one time by using a grid-array method with a 1064 nm laser at different power outputs. The skin injury reaction was observed immediately after laser irradiation from low to high doses. The incidence of skin injury was calculated quantitatively. The healing and pathological changes after laser-induced skin injury were observed dynamically within 6 h and for 28 d after laser irradiation. With the increase of irradiation dose, laser-induced skin injuries ranging from mild to severe appeared in turn. The damage threshold of laser irradiation ED 50 is 47.4 J cm

We demonstrate a simple approach to retrieve the original peak electric field (E-field) strength of high-intensity THz pulses using an electro-optic sampling (EOS) technique and the Poynting flux approach. The latter supposes assessment of THz pulse intensity by measurement of pulse energy, duration and spot size, but its applicability to a few-cycle THz pulse needs detailed consideration. We applied a deconvolution procedure to the raw EOS data to retrieve the THz field waveform. We describe a two-step procedure that allows us to assess the field strength of an extreme THz field. First, the EOS measurements of the THz field should be performed at low pulse energies to retrieve the THz waveform and estimate pulse duration and amplitudes of each particular oscillation. Next, the field strength of an extreme THz pulse can be assessed from the Poynting flux approach with correction to the abovementioned data obtained from the EOS measurements. We show good experimental coincidence ...

We demonstrate a fiber-optic source of random numbers in which random-number generation (RNG) is implemented via an inherently quantum process—detection of correlated photon pairs produced by spontaneous four-wave mixing (FWM) inside an optical fiber. The detection times of individual photon pairs, generated in our RNG scheme via phase-matched FWM in a highly nonlinear photonic-crystal fiber with a suitable dispersion profile, are converted into megabit-size binary sequences, serving as strings of random numbers. The randomness of these bit strings is verified by the National Institute of Standards and Technology Statistical Test Suite. We identify FWM regimes in which mode-locked short-pulse laser sources can provide a high peak power needed to drive photon-pair generation in optical fibers without an excessive loss of randomness due to unwanted patterns in the RNG photon-pair output.

This paper presents a method aimed at encrypting color images using vector operations and secondary image phase masks (SPMs). In this encryption, the optical coherent superposition principle is used to separate and overlay the original image into two phase plates on the three channels R, G and B, respectively. Then the double random phase encoding in the Fresnel domain is performed using the SPMs to encrypt one of the phase plates. Finally, the Kronecker product of two random matrices is directly perform randomization on the encoded image, achieving multilevel encryption of color images. Computer simulations are presented to demonstrate its performance, and the feasibility and security of the proposed system are analyzed as well.

For the practical Faraday mirror (FM) in a continuous-variable quantum key distribution (CVQKD) system there exists a rotation angle deviation that can lead to a loss of photon number when a light message passes through the polarization beam splitter. Here we employ the entanglement-based model to research the influence of the FM’s imperfection. Based on parameter estimation, the imperfection can introduce a loophole for Eve to obtain information. The secret key rate of the CVQKD will be impaired. Finally, a novel method is proposed to ensure system performance by compensating optical power, and we further study the relationship between the secret key rate and the modulation variance.

In this letter, we investigate quantum correlations (quantum discord, concurrence and Bell nonlocality) in an open system (amplitude damping channel) with the Unruh effect under a Schwarzschild space-time. In an amplitude damping (AD) channel, we can discover that the Hawking–Unruh effects and decoherence will influence these quantum correlations. However, quantum correlations always decrease with increasing the AD decoherence strength, irrespective of whether there are Hawking–Unruh effects. The results also indicate that the impact of the AD decoherence on quantum correlations is stronger than that of the Hawking–Unruh effects. Besides, we find that if concurrence is present, Bell nonlocality may disappear. This means that the Bell nonlocal states are a strict subset of the entangled states. Furthermore, the redistributions of quantum correlations are discussed in detail under a Schwarzschild space-time. The results show that the reduced physically accessible quantum correlati...

The treatment of infected, long-term, non-healing, complicated wounds of the skin and mucosa, trophic ulcers, pressure sores and ulcers of diabetic feet represents a serious problem, especially in the case of resistant and multi-resistant pathogens. Antibacterial photodynamic therapy can be a promising method of local infected foci treatment of such diseases. This work is devoted to the study of the possibility of photodynamic inactivation (PDI) of Pseudomonas aeruginosa bacteria in the form of biofilms with the help of new polycationic photosensitizers (PSs) based on octacationic phthalocyanine and tetra- and octabacteriochlorins (ZnPcChol 8 , (3-PyBrE) 4 BCBr 4 and (3-PyEPy) 4 BCBr 8 ). More specifically, this work aims to clarify the role of light irradiation in PDI with the participation of new PSs, which has not been fully studied, especially with respect to the comparison of different PS types.

In this paper, a high-power Ho:YAG laser in-band pumped by a Tm-doped fiber laser at 1931 nm is reported. A maximum output power of 142.2 W is achieved at 2091 nm using a single-end-pumped configuration, corresponding to a slope efficiency of 56.7%. This is, to the best of our knowledge, the highest output power directly generated by bulk Ho-oscillators in the 2.1 µ m spectral region.

Neutron detection finds wide use in various areas, thus the improvement of the relevant instruments and methods has been focused on for a long time. For the purpose of detecting possible neutrons, in the present paper, we theoretically put forward a carbon nanotube (CNT) sensor based on a single nitrogen-vacancy center coupled to a current-carrying CNT to detect neutrons. With two lasers applied, the accreted mass landing on the nanotube may cause a frequency shift in the probe absorption spectrum. Once the frequency shift is measured, the added mass will be determined. Through the use of this sensor, owing to the small effective mass and high quality factor of the CNT, an ultrahigh mass resolution could be achieved. Due to its ultrahigh resolution, the sensor can be used to detect neutrons. Furthermore, we provide a brand new optical approach for neutron detection.

The 1st, 2nd and 3rd order least square method (LSM-1, LSM-2 and LSM-3) is applied to smooth the experimental absorption signal of 13 CO 2 and 12 CO 2 obtained by the tuneable diode laser absorption spectroscopy method in the 4860–4880 cm −1 frequency range of a tuneable diode laser. It has been shown clearly that using LSM-2 with a filter window N ~ 100 allows the 13 CO 2 content in exhaled air to be measured at an error level of 0.28%, which meets breathing tests requirements.

In this paper we consider a method for researching the dynamics of blood flow in the cerebral cortex, on an optical phantom that reproduces the parameters of real human and mice brain structures, through the use of near and infrared ranges of laser radiation. For the investigation of real tissue we chose a laboratory mouse brain in vivo . An algorithm for non-invasive diagnostics of the degree of oxygenation was identified and optimal parameters of installation components were selected for taking information about hemodynamic indicators. Output was verified by the reference method for assessing oxygenation by degree of absorption of hemoglobin in the visible range, which indicates that data have a high correlation with classical methods. With further development, this algorithm can be used in various areas of research and diagnostics.

A high-repetition-rate single-frequency injection-seeded Q-switched Er:YAG laser with a ‘double reflection’ architecture is reported. Single-frequency laser pulses at a pulse repetition frequency (PRF) of 2 kHz are obtained by using ‘ramp-fire’ injection-seeding technique. The half-width of the pulse spectrum is measured to be 2.05 MHz by using the heterodyne beating technique. The novel ‘double-reflection’ architecture is employed in order to achieve a stable high-repetition-rate single-frequency operation. As far as we know, 2 kHz is the highest PRF achieved from a single-frequency, injection-seeded Q-switched Er:YAG laser that can be used in a wind Lidar system.

We reported a multi-watt ~2.1 µ m laser output from a 30 cm long Ho 3+ -doped fluorotellurite microstructured fiber (FTMF) pumped by a homemade 1980 nm Tm 3+ -doped silica fiber laser. When the pump power was increased to 61.8 mW, lasing at 2067 nm was achieved from the Ho 3+ -doped FTMT, and an unsaturated maximum output power of ~8.08 W was obtained for a pump power of ~10.56 W. The corresponding slope efficiency was about 77.21%. During our experiments, no obvious damage was observed on the end face of the Ho 3+ -doped FTMF. Our results indicated that Ho 3+ -doped fluorotellurite fibers had the potential for constructing high power fiber lasers at 2.1 µ m.

We theoretically investigate the high-order harmonic generation (HHG) from laser–solid interaction in a doped semiconductor by solving the one-dimensional time-dependent Schrödinger equation within the single active electron model. The results show that the energy band of the valence and the low conduction band can be split into a small band in the doped semiconductor. The splitting band gap can be controlled by changing the depth of the potential well of the doped semiconductor, and the second HHG plateau can be enhanced. We also demonstrate the energy band structures in coordinate space with different numbers of dopant. Time-dependent population imaging is used to illustrate the change of the splitting band gap with different depths of the potential well of the doped semiconductor.

The present work gives a brief review of the nonlinear χ(2)‐ and χ(3)‐lasing properties of SRS‐active natural crystals (minerals) known so far. This compilation complements new results of a detailed investigation of Raman induced χ(3)‐effects in aragonite single crystals (orthorhombic CaCO3) under single‐ and dual‐wavelength picosecond excitation in the UV, visible and near‐IR spectral ranges. The studied effects at room and cryogenic temperatures comprise Stokes and anti‐Stokes combs of almost two octaves bandwidth, THG, SFG, as well as cascaded and cross‐cascaded χ(3) ↔ χ(3) interactions. All recorded lasing χ(3)‐components were identified and attributed to three observed SRS‐promoting vibration modes ωSRS 1 ≈ 1087 cm–1, ωSRS 2 ≈ 152 cm–1, and ωSRS 3 ≈ 205 cm–1 (at room temperature) of aragonite. Stimulated Raman scattering (SRS) investigations of minerals so far enrich the arsenal of SRS‐active crystals, which can be applied to solve fundamental and applied tasks of modern laser physics and nonlinear optics. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)

Spectroscopic properties and continuous‐wave laser performance of a new Yb0.015:Lu0.162Gd0.823VO4 mixed vanadate crystal are reported. An appreciable discontinuous increase in output power occurs during the σ ‐ to π ‐polarization switching process in the laser oscillation. A maximum output power of 4.3 W is generated with an optical‐to‐optical efficiency of 46%, whereas the average slope efficiency is determined to be 73–77%, depending on the output coupling utilized. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)

A compact diode‐pumped solid‐state Tm:KY(WO4)2 laser with cavity length of 1 cm passively Q‐switched with a PbS‐quantum‐dot‐based saturable absorber is presented. The laser operates at the wavelength of 1.94 µm and produces pulses with duration of 8 ns and energy of 30 µJ at the repetition rate up to 4.2 kHz. The maximum output power of 120 mW is achieved at incident pump power of 1.15 W. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)

Intra‐cavity frequency doubling of continuous‐wave (CW) laser emission on the quasi‐three level (4F3/2 → 4I9/2) laser transition of Nd3+ in Nd:GGG is reported by using a three‐mirror folded resonator. The thermal lens experienced by the optically‐pumped Nd:GGG laser crystal is measured as a function of the absorbed pump power and compared to that found, in the same conditions, in the case of Nd:YAG. Results are interpreted by using a simple model accounting for the absorbed pump power and the thermo‐mechanical properties of each laser crystal. Diode‐pumped blue laser operation is achieved, for the first time, at 467.0 and 468.5 nm with output powers of 230 and 450 mW, respectively. Simultaneous laser operation resulting both from frequency‐doubling and frequency summing at the three 467.1, 467.7, and 468.1 nm laser wavelengths is also obtained with a total output power of 60 mW. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)

The characterization of new gain‐switched Fe:Cr:Zn1–xMgxSe laser working at the room temperature and its comparison to Fe:ZnSe laser was performed. The laser oscillation behavior, generation efficiency and output wavelength tuning possibilities were demonstrated. It was shown that the absorption and luminescence spectra of Fe:Cr:ZnMgSe crystal are shifted towards longer wavelengths in comparison with Fe:ZnSe active material. The difference is approximately 300 nm and it corresponds to measured absorption and emission spectra. The maximal Fe:Cr:ZnMgSe laser generated energy and the slope efficiency with respect to the absorbed energy were 200 µJ and 4.5%, respectively. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)

Multiple Stokes and anti‐Stokes χ(3)‐nonlinear generation in the tetragonal crystal of CaYAlO4 was observed at 300K and ≈9K under picosecond excitation in the visible spectral range. All the recorded Raman induced laser lines were identified and attributed to the SRS‐promoting vibration mode of octahedral [AlO6]–9 units of the crystal. (© 2012 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)