We propose the obtaining of the 3D shapes by scanning with a light line of generated digitally Gaussian, triangular or sinusoidal profile. Algorithms based on the Bezier curves, linear regression, and nonlinear regression methods were implemented, which allowed to obtain the skeleton of each line of light captured with sub-pixel accuracy. The height measurements obtained with each projected profile

We report a compressive interference-based encryption (IBE) method using sparsity constraints. In this method, two sparse phase-only masks (POMs) are generated through a modified phase retrieval algorithm under the constraints of two complementary binary amplitude masks (BAMs), and then fused into one ciphertext. For the decryption in the IBE system, the ciphertext bonded with one BAM is placed in

In this paper we propose super resolution measurement and post-processing strategies that can be applied in thermography using laser line scanning. The implementation of these techniques facilitates the separation of two closely spaced defects and avoids the expected deterioration of spatial resolution due to heat diffusion. The experimental studies were performed using a high-power laser as heat source

A high-precision and strain-free semi-kinematic mount has been proposed in this research for ultra-precision optical systems. The mount includes three identical feet. Each foot constrains the axial and the tangential direction of the lens motion. Three feet in combination precisely control the six degree-of-freedom (6-DOF) motion of the lens. A strain-free mount of the lens was obtained and the high-precision

In this paper, we propose a fringe analysis method to address the problem of phase retrieval from interferogram corrupted with fringe amplitude non-uniformity, and show its practical application for nanoscale surface profilometry. The proposed method relies on the implementation of second order optimization combined with total variation regularization using graphic processing unit based computing.

The development of high-resolution THz imaging systems is currently of great practical significance, (e.g. in the areas of security, agri-food, biomedicine etc.). Implementing and calibrating such systems is essential, as is the verification and appropriate use of models. Confocal microscopes are well known to improve resolution and provide 3D images. In this paper a novel terahertz (THz) confocal

Intensity-modulated linear imaging spectropolarimetry can measure a two-dimensional distribution of spectrally-resolved linear Stokes parameters in a single-shot polarization modulation. However, the state-of-art reconstruction method, Fourier transform method (FTM), usually transforms the modulated spectrum into the frequency domain for further processing. As a result, there is channel crosstalk issue

Digital fringe projection is a surface-profiling technique that is gaining popularity due to the increasing availability and quality of low-cost projection equipment and digital cameras. Noise in the pixel field of imaged targets induces error in the reconstructed phase and ultimately the surface profile measurement. In this paper, we present an approximate analytical probability density function for

In this paper, we introduce a spectrometer design with crossed double-grating for extracting pure rotational Raman (PRR) lines of N2. The design applies a linear optical fibre array as the entrance slit and a linear array photomultiplier tube (LaPMT) as the detector. The linear dispersion and structural parameters of the proposed configuration were analysed theoretically, and the optical layout of

Structured light three-dimensional (3D) measurement technology is considered one of the most reliable 3D data acquisition methods. Driven by the demand for high-precision 3D data acquisition for miniaturized samples in many fields such as surface condition analysis, mechanical function test, and micro-electro-mechanical systems (MEMS) quality inspection, microscopic fringe projection profilometry (MFPP)

Spectral interference and self-absorption seriously affect the accuracy of quantitative analysis in laser-induced breakdown spectroscopy (LIBS). In this work, we used LIBS assisted with laser-stimulated absorption (LSA-LIBS) to solve these problems. Taking nickel (Ni) in the alloy structural steel as an example, the results show that the spectral interference of Ni lines was eliminated, the self-absorption

In a traditional time-domain ghost imaging system, it is necessary to employ a Fourier transformation to obtain the spectral information of a signal when the time-domain signal is recovered. In this paper, a new technology combines the characteristics of time-domain ghost imaging and a Fourier transform and uses the time-varying light intensity, which has a definite sinusoidal and cosine distribution

Fringe projection profilometry (FPP) using a vertical scanning setup has the merit of avoiding occlusions and shadows over triangulation based approaches. However, very few methods with a vertical scanning setup has revealed the supporting physical model to explicate the relationship between depth and the level of defocus of fringe patterns. In this paper, we propose a novel active shape from projection

A low-frequency photoacoustic (PA) sensor based on Parylene-C diaphragm for space-limited trace gas detection is presented. The overall structure of the sensor head includes a cylindrical brass shell, a Parylene-C diaphragm, and a PA cavity regarded as the Fabry-Perot (F-P) cavity as well. The volume of the PA cavity is only 74 μL. A distributed feedback (DFB) laser is used as an acoustic excitation

The transport of intensity equation (TIE) is an ideal candidate for phase imaging with partially coherent illuminations. TIE has the advantages of simplicity in phase calculation due to its closed-form solution and no requirement for a reference beam and phase unwrapping due to its non-interferometric nature. However, TIE requires multiple through-focus intensity images, and is very sensitive to image

In this paper, a novel optical image encryption and authentication scheme based on partial joint power spectrum (JPS) and phase-retrieval technique has been proposed. In the proposed encryption process, a pure amplitude spatial light modulator (SLM) is utilized to modulate and display the entire input plane comprised with the real-valued plaintext and the amplitude key while the random phase mask (RPM)

As the great application potential of visible light communication (VLC) in the next generation communication after 5G, study of the transmission security in VLC is high desirable with the rapid growth of wireless network traffic. In this paper, an optical encryption scheme for VLC is proposed based on temporal ghost imaging (TGI) with a micro-light-emitting diode (micro-LED). The target temporal signal

This paper presents an image encryption algorithm based on the compressive sensing and a hyperchaotic map, which includes the permutation, compression and diffusion processes. Firstly, the plain image is transformed using discrete wavelet transform, and the coefficient matrix is obtained. Then, the row and column permutation are applied to achieve a good scrambling effect. Secondly, the permuted coefficient

Multiple layers of information security are introduced based on computational ghost imaging (CGI). We show, in the first step, that it is possible to design a very reliable image encryption scheme using 3D computational ghost imaging with two single-pixel detectors sending their data through two channels. It is then shown that further level of security can be achieved by merging data carrying channels

Intravascular optical coherence tomography (IVOCT) has been widely used in clinical coronary artery intervention field. Owing to defocus and contrast agent absorption effects, the intensity fluctuation caused by imaging catheter locating at an eccentric position significantly influence the quality of IVOCT imaging and even plaque type identification. In this paper, we present a novel method to compensate

This article focuses on further developments of the background-oriented schlieren (BOS) technique to visualize convective indoor air flow, which is usually defined by very small density gradients. Since the light rays deflect when passing through fluids with different densities, BOS can detect the resulting refractive index gradients as integration along a line of sight. In this paper, the BOS technique

Due to lower core loss and higher flux density and permeability, thin non-oriented silicon steels are becoming more and more important for soft magnetic materials. Recently, laser has been emerged as a cost-effective tool for machining thin silicon steels, especially for the low-volume and high-variety motor manufacturing. Based on experimental data, this study aims at developing an extreme learning

High-precision axial displacement tracking of trapped beads is an indispensable feature of optical tweezers in advanced single-molecule studies. Here, we demonstrate an alternative method that enables axial calibration and tracking to be carried out on the same sample to avoid unnecessary errors. This method works by applying a dynamic force balance on a bead trapped between a piezoelectrically driven

In the last decades, the understanding of the complex biological mechanisms that regulate the life and growth of single cells and their reciprocal interaction has steadily increased. In this process, Quantitative Phase Imaging (QPI) has emerged as an invaluable tool, thus providing a new way of investigating live cell behaviour in a dynamic, label-free and non-invasive modality. It has proved especially

Interferential optical encoders are promising nano-positioning sensors in precision manufacturing and metrology instrumentation. As measuring standard, the quality of diffraction grating scales primarily determines the performance of the interferential optical encoders. In this work, the optimal design and fabrication of a reflective diffraction grating scale with sine-trapezoidal groove is performed

This paper presents a depth perception system based on one-shot coding structured light method. The designed monochromatic pattern is robust against occlusion and sharp deformation, suitable for dynamic scene, and less sensitive for color interference, with symbol density spectrum (SDS) rule, legitimately increasing number of feature points inside element which further enhancing resolution. For the

In order to study the influence of air gap and focus position on the quality of ps-laser glass-to-glass welding we implemented a method of detecting the air gap between glass surfaces based on optical thin film interference. The method allows real-time optimization of the welding process. We measure the air gap between glass surfaces to be bonded and the laser focal position, which are set as the constraint

Surface distortion reduces the astronomical observation efficiency of large radio telescopes. Based on even-odd phase expansion, we present a semi-analytical phase retrieval algorithm for antennas equipped with an active surface system to detect its surface distortion. In the method, the odd-part distortion is solved directly from the focused far-field pattern, and the even-part is solved by adding

Two are the main limitations of in-line holography: the twin image problem and the poor spatial resolution in the optical axis direction. The twin image problem can be solved with the introduction of an imaging lens and a knife-edge aperture located at its focal plane. In this work, a theoretical analysis of the axial resolution with and without aperture is provided from the perspective of the Optical

A totally automatic and robust phase aberration compensation method is proposed for digital holographic microscopy. The correction needs no manual operation or prior knowledge of the recording setup. As the phase aberrations are modeled with orthogonal polynomials, not only phase curvature but also high order aberrations could be corrected with a single hologram. The polynomial coefficients are obtained

In this paper, we propose an analytical phase retrieval approach applying only phase modulations in the region isolated from the object to be measured. This approach employs a series of intensity-only measurements and can accurately and conveniently achieve phase recovery in the range of [0, 2π) once a reference phase is calibrated in advance. To improve the robustness of the algorithm, this paper

When it comes to “phase measurement” or “quantitative phase imaging”, many people will automatically connect them with “laser” and “interferometry”. Indeed, conventional quantitative phase imaging and phase measurement techniques generally rely on the superposition of two beams with a high degree of coherence: complex interferometric configurations, stringent requirements on the environmental stabilities

In this paper, secure compressive sensing based on a combination of the chaotic discrete wavelet transform (DWT) basis and chaotic discrete cosine transform (DCT) measurement matrix is proposed. In the proposed scheme, a logistic map is employed to generate two chaotic sequences that are used to scramble the rows of the conventional DCT and original DWT matrix to form a chaotic measurement matrix and

This study proposes and demonstrates a compact synthetic aperture digital holographic microscope (SA-DHM) with mechanical movement-free beam scanning and optimized active aberration compensation. The SA-DHM system is equipped with a phase-only liquid crystal on silicon (LCoS) device as an active optical element to achieve a compact mechanical movement-free beam steering architecture with aberration

Ablation material is at the base of the entire aerospace industry. The ablation process is the primary mechanism of thermal protection provided by the ablation material. The mechanical performance of ablation materials across the ablation process is a significant problem for the ablation material research. The combustion phenomenon in the ablation process leads to the failure of the measurement of

The objective of this paper is to fabricate a flexible mid-infrared (IR) light delivery system with bioprobesince remarkable biological effect of mid-IR light and lack of corresponding technical devices. Hollow optical fiber with sealing window of different materials and shapes was fabricated and packaged within a metal tube for delivering mid-IR light and electrical signal. The thickness of the sealing

A novel technique is proposed for circular birefringence (CB) sensing using a surface plasmon resonance (SPR) prism coupler and differential Mueller matrix polarimetry. In the proposed system, the SPR prism coupler is placed in front of the sample in order to generate a weak-scattering medium model and enhance the sensitivity of the measurement process. The CB properties of the sample are then extracted

Contactless measurement of absolute distance or high-frequency vibration is a prominent factor for many industrial & scientific applications like predictive maintenance, non-destructive testing, and reverse engineering, etc. In recent years, self-mixing optical feedback interferometry (SM-OFI) has proven its superiority over other conventional optical methods because of its simple, compact and less

We report a formation of highly homogenous subwavelength grating structures on the bulk Fe-based metallic glass, using two nondegenerate linear polarization of femtosecond laser pulse sequences at certain temporal delays. In contrast to the previous observations, the well-defined surface structures can take place across the entire laser ablation regions, with the spatial period and the modulation depth

The Optical Coherence Velocimeter (OCV) technology is a technique for high-precision displacement and vibration measurement based on the principle of spectral domain optical coherence method. The key of this technology is to realize nanometer or even sub-nanometer measurement by high precision frequency estimation method called as Hanning-window energy centrobaric method (HnWECM). This paper analyses

The absorption and scattering effects of light source during the transmission of biological tissues make it difficult to identify heterogeneity in multi-spectral images. This paper firstly proposes a combination method of modulation-demodulation-frame accumulation technique (MDFAT), spatial pyramid matching (SPM) model and deep learning to realize heterogeneous detection in multi-spectral images. Firstly

For terahertz frequency domain spectrometers (THz-FDS), the effects of Fabry-Perot (FP) interference and system dispersion are inevitable, thus the typical data-analysis methods normally result in large errors in the measurement of the THz transmission spectrum and refractive index of samples. By using the phase relationship between two groups of acquired THz-FDS data with different optical paths,

We propose a deep learning denoising computational ghost imaging (CGI) method to obtain a clear object image with a sub-Nyquist sampling ratio. We develop an end-to-end deep neural network (DDANet) for CGI image reconstruction. DDANet uses a one-dimensional (1-D) bucket signals (BSs) and multiple tunable noise-level maps as input, and outputs a clear image. We train DDANet with simulated BSs and ground-truth

Diffraction imposes a barrier to resolve objects smaller than half the wavelength used to illuminate them. In optical microscopy, this barrier was surpassed 25 years ago. One form of achieving super-resolution is the use of complex-amplitude pupil masks. Spatial light modulators can be used to produce these masks, if we compensate the aberrations introduced by them. In this paper we propose a method

For many three-dimensional (3D) measurement techniques based on fringe projection profilometry (FPP), measuring the objects with a large variation range of surface reflectivity is always a very tricky problem due to the limited dynamic range of camera. Many high dynamic range (HDR) 3D measurement methods are developed for static scenes, which are fragile for dynamic objects. In this paper, we address

CW Range-resolved S-lidars (the S symbol comes from Scheimpflug) have gradually evolved into a new class of laser sensors for remote environmental monitoring and a potential alternative to traditional atmospheric lidars. Based on the biaxial optical scheme, they sense the environment by continuous-wave laser emitters, implement the triangular principle of range control and use position-sensitive photodetectors

Quantification of fringe orders is important in visualizing full-field stress in digital photoelasticity. Various methods have been developed to improve the calculated accuracy of fringe orders, such as the phase shifting, carrier, and RGB methods. However, in these methods, fringe orders are calculated using the photoelastic patterns under a certain load but not the patterns in the whole time series;

Low scattering media is the best scenario for optical imaging in thick samples and deep tissue, as it allows to obtain high resolution images without suffering the limitations that the diffusion phenomenon imposes. The high contribution of ballistic light in this regime enabled the development of light sheet microscopy and optical projection tomography, two of the most common techniques nowadays in

Amorphous alloys have great potential in industrial applications. However, metallurgical characteristics of those materials during laser welding are still unclear. In this research, pulsed Nd:YAG laser welding was performed on the β-Ti dendrite reinforced amorphous alloy plates. The microstructures of the welding joints were specially observed and analyzed. Results show that no metallurgical defects

We report a scheme to generate radially polarized THz radiation by frequency difference of Hermite Cosh Gaussian lasers in hot electron, collisional and density modulated plasma. The effect of laser (spatial field distribution) and plasma parameters (plasma density structure, electron-neutral collisions and electron temperature) on emitted THz field profile is investigated. We found that THz field

In this paper, we report an optical system that can effectively enhance the resolution of continuous-wave (CW) stimulated emission depletion (STED) microscopy by applying an amplitude-modulated azimuthally polarized light with vortex phase (AV) as an excitation beam. Based on the vector field diffraction theory, we analyzed electric fields near the focal plane for various polarization states and rotationally

In this paper, a super multi-view display based on a diffractive optical element with pixelated nanogratings is proposed to solve the vergence-accommodation conflict in three-dimensional displays. The diffractive optical element can modulate the phase information of a three-dimensional scene to form a series of viewing points under the illumination of a point light source. By designing the vector of

Calibration of a stereo vision system is essential for three-dimensional shape and deformation measurements. Although the target-based calibration technique is a good solution, it comes with limitations in a large field of view (FOV) measurement due to the target size and difficulties in operation. In this paper, a method using the inertial measurement unit (IMU) has been proposed to calibrate stereo

Polarization imaging is a promising technology with great potential. Besides light intensity, it provides information in another dimension, polarization. When imaging through water, two frames of the target at two orthogonally polarized states, Imax and Imin, are needed. In most experiments, they are determined by searching for the darkest and brightest moments during polarizer rotation. But in cases

In the last three decades of developments, the technique of Digital Photoelasticity (DP) has been stabilized and the methodology has been successfully applied to a wide range of problems in Engineering and science. This review succinctly summarizes both the techniques and their applications. Sufficient attention is paid to bring out the problem-solving capability of photoelasticity in each of the domains

Wind turbine blades play a key role in the wind energy collection system. Deformation measurement for turbine blades is an important and efficient way to prevent blade damages. Here, a novel and low-cost measurement method of static deformation for wind turbine blades using home-made LiDAR was proposed, and then verified by measuring the flap-wise load bending of a wind turbine blade model. The horizontal

Based on the extended Huygens-Fresnel principle, the analytical expressions of the spectrum for Gaussian-Schell model vortex beam (GSMVB) propagating in biological tissues have been derived. The effects of the field point position, the species of the biological tissues, spatial correlation of beams on the relative spectral shift of GSMVB passing biological tissues have been investigated using the contour

Biospeckle is caused by statistical interference of coherent beam reflected from a surface having temporal variation due to physiological or biochemical activity. For quantitative evaluation of underlying dynamic speckle activity, different point based and full-field indexing based techniques were proposed in the literature. However, most of the existing techniques involve manual region of interest

Over the past years, we have been developing new algorithms and approaches for robust, efficient and accurate internal displacement and strain field measurements using digital volume correlation (DVC). This paper will summarize our recent work on the following four major aspects: (a) advanced three-dimensional inverse-compositional Gauss-Newton (3D IC-GN) algorithm for subvoxel registration with enhanced

During the decade of the 1940’s, an interferometric technique was sought capable of ameliorating the intrinsic aberrations present in electron microscopes. Such technique, used with ad-hoc experimental conditions, gave birth to the field of holography. The capabilities of holography allow the precise reconstruction of a wavefront distorted by a particular sample under observation. At that time, the