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We present an imaging method that uses the random optical speckle patterns that naturally emerge as light propagates through strongly scattering media as a structured illumination source for photoacoustic imaging. Our approach, termed blind structured illumination photoacoustic microscopy (BSIPAM), was inspired by recent work in fluorescence microscopy where super-resolution imaging was demonstrated using multiple unknown speckle illumination patterns. We extend this concept to the multiple scattering domain using photoacoustics (PA), with the speckle pattern serving to generate ultrasound. The optical speckle pattern that emerges as light propagates through diffuse media provides structured illumination to an object placed behind a scattering wall. The photoacoustic signal produced by such illumination is detected using a focused ultrasound transducer. We demonstrate through both simulation and experiment, that by acquiring multiple photoacoustic images, each produced by a different random and unknown speckle pattern, an image of an absorbing object can be reconstructed with a spatial resolution far exceeding that of the ultrasound transducer. We experimentally and numerically demonstrate a gain in resolution of more than a factor of two by using multiple speckle illuminations. The variations in the photoacoustic signals generated with random speckle patterns are utilized in BSIPAM using a novel reconstruction algorithm. Exploiting joint sparsity, this algorithm is capable of reconstructing the absorbing structure from measured PA signals with a resolution close to the speckle size. Another way to excite random excitation for photoacoustic imaging are small absorbing particles, including contrast agents, which flow through small vessels. For such a set-up, the joint-sparsity is generated by the fact that all the particles move in the same vessels. Structured illumination in that case is not necessary.

Angular resolved scattering light measurements on chromosomes are compared to Discrete Dipole Approximation (DDA) simulations using Atomic Force Microscopy (AFM) based geometrical models. This could present a novel, marker-free method for human chromosome karyotyping.

We significantly improve the estimation of the absorption and reduced scattering coefficients, and second-order similarity parameter γ from spatially resolved reflectance by extending the inverse model with the third-order similarity parameter δ.

Utilizing a modified analytical solution of the radiative transfer equation allows to fit both the spatial frequency domain reflectance and the phase. The additional information then allows to correct for surface reflections.

Bessel beam has the advantages of reducing scattering artefacts and increasing the quality of the image and penetration. This paper proposed to generate a guide star by Bessel beam with vortex phase, and to use the beacon with special spot structure to measure the atmosphere turbulence aberrations. With the matching algorithm of measured characteristic spot in each subaperture, the detection accuracy of Hartmann wavefront sensor can be improved. Based on wave optics theory, the modeling of Bessel beam guide star and wavefront sensing system was built. The laser guide star beacon generated by Bessel beam with vortex phase and beacon echo wave measured by Hartmann sensor were both simulated. Compared with the results measured by echo wave from Gauss beam generated guide star beacon, this novel method can reduce the error of wavefront detection and increase the detection accuracy of Hartmann sensor.

Studying propagation of light in random scattering materials is important for both basic and applied research. Such studies often require usage of numerical method for simulating behavior of light beams in random media. However, if such simulations require consideration of coherence properties of light, they may become a complex numerical problems. There are well established methods for simulating multiple scattering of light (e.g. Radiative Transfer Theory and Monte Carlo methods) but they do not treat coherence properties of light directly. Some variations of these methods allows to predict behavior of coherent light but only for an averaged realization of the scattering medium. This limits their application in studying many physical phenomena connected to a specific distribution of scattering particles (e.g. laser speckle). In general, numerical simulation of coherent light propagation in a specific realization of random medium is a time- and memory-consuming problem. The goal of the presented research was to develop new efficient method for solving this problem. The method, presented in our earlier works, is based on solving the Fredholm type integral equation, which describes multiple light scattering process. This equation can be discretized and solved numerically using various algorithms e.g. by direct solving the corresponding linear equations system, as well as by using iterative or Monte Carlo solvers. Here we present recent development of this method including its comparison with well-known analytical results and a finite-difference type simulations. We also present extension of the method for problems of multiple scattering of a polarized light on large spherical particles that joins presented mathematical formalism with Mie theory.

Polarimetric characteristics of light from ocean water in combination with standard remote sensing reflectance provide important information about water constituents; they are useful in retrieval of additional water parameters like attenuation-to-absorption ratio and attenuation coefficients and/or establishing additional constraints for retrieval algorithms. The Stokes vectors of light above and below the water surface, which fully represent polarimetric characteristics of water leaving radiance, strongly depend on the particle size distribution and related Mueller matrices of water particulates. In this work we investigate the effect of various hydrosol mixtures of chlorophyllous particles on the polarized light field. The Stokes vectors of scattered light and the degree of polarization (DOP) are generated as outputs of vector radiative transfer simulations for various water compositions. Mie theory as well as T-matrix approaches are used for the generation of scattering matrices. The impact of their variability on the Stokes vectors of polarized light is analyzed.

We present a method for holographic imaging through a volume scattering material, which is based on selfreference and light with good spatial but limited temporal coherence. In contrast to existing techniques, we do not require a separate reference wave, thus our approach provides great advantages towards the flexibility of the measurement system. The main applications are remote sensing and investigation of moving objects through gaseous streams, bubbles or foggy water for example. Furthermore, due to the common path nature, the system is also insensitive to mechanical disturbances. The measurement result is a complex amplitude which is comparable to a phase shifted digital hologramm and therefore allows 3D imaging, numerical refocusing and quantitative phase contrast imaging. As an example of application, we present measurements of the quantitative phase contrast of the epidermis of an onion through a volume scattering material.

Scattering environment conditions, such as fog, pose a challenge for many detection and surveillance active sensing operations in both ground and air platforms. For example, current autonomous vehicles rely on a range of optical sensors that are affected by degraded visual environments. Real-world fog conditions can vary widely depending on the location and environmental conditions during its creation. In our previous work we have shown benefits for increasing signal and range through scattering environments such as fog utilizing polarized light, specifically circular polarization. In this work we investigate the effect of changing fog particle sizes and distributions on polarization persistence for both circularly and linearly polarized light via simulation. We present polarization tracking Monte Carlo results for a range of realistic monodisperse particle sizes as well as varying particle size distributions as a model of scattering environments. We systematically vary the monodisperse particle size, mean particle size of a distribution, particle size distribution width, and number of distribution lobes (bi-modal), as they affect polarized light transmission through a scattering environment. We show that circular polarization signal persists better than linear polarization signal for most variations of the particle distribution parameters.

A one-shot multi-directional ultra-small angle X-ray scattering imaging successfully resolves the fiber orientation of a wood sample. This 2D structured illumination enables the retrieval of scattering signals in multiple directions simultaneously.

The coherence matrix from the scattering matrix of a single look polarimetric SAR pixel will have an entropy of zero with the main eigenvalue being equal to the span and the other two eigenvalues being equal to zero. Each scattering matrix element from terrain scatter is a coherent sum from a large number of scatterers in a resolution cell. Entropy/alpha decomposition is only possible where the coherency matrix elements are determined from ensemble covariances. This is the case for multilook polarimetric SAR data where covariances from the exact same collection of scatterers are averaged using separate extraction filters in the SAR doppler direction. We report interesting observations from analysis of multilook SIR-C data at L and C bands from different oceans around the globe. We present a strategy for segmenting single look polarimetric TerraSAR ocean data using an algorithm we have previously developed with the averaging of the resulting like pixels used to generate coherence matrices. We give a brief discussion of desert surfaces.

We propose and demonstrate the use of cross recurrence plot analysis (CRPA) to accurately determine the Brillouin shift due to strain and temperature in a Brillouin distributed fiber sensor. This signal processing technique, which is implemented in Brillouin sensors for the first time relies on apriori data i.e, the lineshape of the Brillouin gain spectrum and its similarity with the spectral features measured at different locations along the fiber. Analytical and experimental investigation of the proposed scheme is presented in this paper.

A novel and simple analytical expression to describe the Brillouin gain spectral broadening as a function of the spatial resolution in time-domain Brillouin distributed fiber sensors is deduced. The proposed model is experimentally validated using a pump-probe Brillouin sensing setup and also compared with numerical and approximate results. In addition, a compact mathematical form is presented for the peak gain reduction resulting from incomplete acoustic-wave activation in Brillouin sensors with short spatial resolution. Both mathematical expressions can be used together to quantitatively predict the impact of the spatial resolution on the signal-to-noise ratio and frequency uncertainty of the sensor.

A novel BOTDA method based on differential π-phase-shift-pulse pair is proposed for narrowing the Brillouin gain spectrum. Theoretical analysis and experimental results demonstrate that the proposal could achieve 17 MHz Brillouin gain spectrum linewidth with a fixed spatial resolution of 2.5 m. The Brillouin gain spectrum linewidth is 3 times narrower than that obtained using conventional single-pulse based BOTDA method with same spatial resolution, resulting in √3 times frequency accuracy improvement. Furthermore, the sharper rising/falling edge of the Brillouin frequency shift profile resulting from the narrowed Brillouin gain spectrum could obtain more precise temperature/strain information along the fiber.

We introduce a new technique to extend the dynamic range of coherent BOTDA sensors in dynamic measurements. It is based on launching pump pulses containing multiple frequencies so that the Brillouin spectra that they generate overlap, allowing to measure larger Brillouin frequency shift variations. Furthermore, this technique is compared to the procedure of shortening the length of the pulses, which also leads to a broadening of the spectra. We analyze both techniques, obtaining a threefold increase in range up to 400 MHz (±4000 μe).

A frequency-domain method is proposed to measure the inertial response of forward stimulated Brillouin scattering, so that the acoustic impedance of a liquid medium outside an uncoated 30 m standard single-mode fibre can be sensed. The proposed technique overcomes the linewidth distortion present in the time-domain approach due to Kerr effect and reduce time and complexity for data post-processing. Experimental results demonstrate that acoustic impedances of water and ethanol agree well with the expected values.

We propose a novel method to increase sensing points of Brillouin optical correlation domain analysis (BOCDA) by utilizing degenerated four-wave-mixing (FWM) process. A sinusoidally frequency-modulated lightwave is used as the pump of FWM, and the generated idlers have a broadened frequency modulation span. The idlers produced by FWM are used in BOCDA system to increase the sensing points of BOCDA since the number is proportional to the frequency modulation span of the laser source. We experimentally demonstrate a modulation span of 74 GHz by using the first-order idler produced by FWM process, which is the largest frequency modulation span achieved in BOCDA system, doubling the sensing points of BOCDA from 1936 to 3872. It provides a possibility to use this method in the state-of-art BOCDA system to achieve several millions of effective sensing points.

We experimentally generate the Bessel-Gauss coherence functions using the cross-correlations between the two speckle patterns obtained using the perfect optical vortices (POV) of different orders. POV beams are generated using the Fourier transform of Bessel-Gauss beams by displaying the axicon hologram on spatial light modulator. A ground glass plate is used for scattering POV beams and the speckles are recorded. The cross-correlation function of two speckle patterns is Bessel-Gauss functions whose order is given by the difference in the orders of two POV beams used for scattering. The auto-correlation function of these speckles is Bessel-Gauss function of order zero.

Partially coherent beam is generated by imposing dynamic random phase to completely coherent beam. The coherence of partially coherent beam can be controlled by the randomness of random phase. The speckle pattern of the partially coherent beam passing through scattering medium is studied. The speckle pattern can be modulated into a bright focal spot by wavefront shaping. The influence of the coherence on the focusing is investigated.

As the industry continues to progress along the ITRS roadmap, not only the device dimensions shrink, but the architectures also increase in 3D complexity. Therefore, new metrology approaches for small structures are required. Small angle X-ray scattering has the potential for fast in line metrology but suffers from the large spot size needed in grazing incidence reflection and the low signal for the transmission geometry. Turning the incidence angle closer to normal and tuning the wavelengths into the EUV spectral range allows to decrease the spot size while keeping the signal high. We present an exploration of soft X-ray and EUV-scatterometry from grazing to near normal incidence, including a new approach in the design of metrology targets to avoid the footprint problem in grazing incidence geometry. Measurements were performed on e-beam written silicon gratings. The reconstructed geometrical line shape models are statistically validated by applying a Markov-Chain Monte Carlo sampling technique. Experimental data and simulation results provide a first insight into the potential of EUV Scatterometry.

Random changes in the polarization states of partial contributions to the multiple scattered light fields in a random medium are analyzed using the statistical modeling of polarized light transport in the medium. The mapping of local polarization states on the Poincare sphere surface clearly indicates the different scenarios of the "order – disorder" transition in the case of Rayleigh and Mie scatterers. If the random medium consisting of small particles is probed by a linearly polarized laser beam, then propagating partial waves keep their linear polarization state but the dispersion of azimuth angles rapidly increases with the increasing average propagation path for these waves. On the contrary, the multiple scattering by random ensembles of the large particles is accompanied by random transformations of the linear polarization of propagating waves to the elliptical polarization. The obtained results are considered in the relation to the known features of polarization decay in the random media.

A method of optical coherence tomography (OCT) structural images reconstruction using Monte Carlo simulations is described. Biological object is considered as a set of 3D elements that allow simulation of media, structure of which cannot be described analytically. Each voxel is characterized by its refractive index and anisotropy parameter, scattering and absorption coefficients. B-scans of the inner structure are used to reconstruct a simulated image instead of analytical representation of the boundary geometry. Henye-Greenstein scattering function, Beer-Lambert-Bouguer law and Fresnel equations are used for photon transport description. Efficiency of the described technique is checked by the comparison of the simulated and experimentally acquired A-scans.

The regularities of movement of the Photon Density Normalized Maximum (PDNM) in highly scattering media such as biological tissues are described. An improved model of the optical properties of turbid media based on the diffusion approximation to the Radiative Transfer Equation (RTE) is used for identifying regularities of PDNM movement. Numerical simulations confirmed that in homogeneous cylindrical objects PDNM always moves to the geometric centre of the object. In the case of single absorbing inhomogeneities PDNM moves towards the point which is symmetrical to the geometric centre of it with respect to the center of the object. In the presence of a single scattering inhomogeneity PDNM moves towards its geometric centre.

The backward scattering characteristic of the jet engine nozzle is one of the most challenging problem in applied electromagnetics. Radar cross section (RCS) data of a double S-shaped nozzle (DSN) with and without radar absorbing material (RAM) were measured in the microwave chamber using stepping test system. The experiment results show that S-shaped structure has a certain effect on the backwards scattering characteristics. Coating RAM can reduce the RCS of DSN effectively.

Large-bipolaron superconductivity is plausible with carrier densities well below those of conventional metals. Bipolarons form when carriers self-trap in pairs. Coherently moving large-bipolarons require extremely large ratios of static to optical dielectric-constants. The mutual Coulomb repulsion of a planar large-bipolarons paired carriers drives it to a four-lobed shape. A phonon-mediated attraction among large-bipolarons propels their condensation into a liquid. This liquids excitations move slowly with a huge effective mass. Excitations concomitant weak scattering by phonons produces a moderate low-temperature dc resistivity that increases linearly with rising temperature. With falling temperature an energy gap opens between large-bipolarons excitations and those of their self-trapped electronic carriers., Comment: 16 pages including 15 figures: Written version of invited talk for 2017 SPIE OPTO meeting Superconductors 1

Natural light will be partially polarized or totally polarized after the reflection, scattering, absorption and refraction of the objects. When detecting the ocean from the satellite orbit, the remote sensing signal of water is mainly composed of three parts: radiation signals of atmosphere after photon scattering, the direct reflection of light when the sunlight reaches the surface of the water, and the light after scatting backward. The sunlight will be polarized when it passes the atmosphere. Also, the polarization state of the incident light will be changed when it passes in the water. For remote sensing cameras with quantitative detection application, it is necessary to suppress the polarization sensitivity of the system as far as possible. Through the layout of the optics, the film layer design, the design of the depolarizer, we can achieve low polarization sensitivity.

We have proposed a novel scattered light computation microscopy (SLCM) that takes use of scattered light in imaging objects shaded by strongly scattering media. Based on the principle of light reciprocity, image is formed through computation in the SLCM method. Compared to the conventional scattered light fluorescence microscopy (SLFM) method, the SLCM doesn’t need any pretreatment of objects. Simulation results have shown that subwavelength resolution can be achieved through the SLCM with optimized parameters. The good anti-noise capability of the SLCM is demonstrated by simulation as well.

In this paper, a broadband, ultrathin metamaterial absorber (MA) using randomly distributed scatterers is presented. Each scattering element consists of two parallel strips. These elements can either be isolated or they may overlap with nearby elements. Three different randomly positioned structures are investigated for normal incident angle as well as oblique incident angles showing that these MAs can provide broadband absorption for all cases. The results presented here coincide with some previous works. Each structure obviously has different absorption spectrum and FWHM since the coupling between the randomly positioned scatterers is different in each case. The coupling between neighboring isolated and clustered scatterers form many resonating modes resulting in broadband absorption. The distribution of the electromagnetic fields are analyzed to obtain the physical behavior of the absorber. This shows that promising results can still be obtained for MAs when there is a significant tolerance distance between scatterers due to fabrication errors in micro and nanoscale metadevices.

We present single-shot real-time video recording of light scattering dynamics by second-generation compressed ultrafast photography (G2-CUP). Using G2-CUP at 100 billion frames per second, in a single camera exposure, we experimentally captured the evolution of the light intensity distribution in an engineered thin scattering plate assembly. G2-CUP, which implements a new reconstruction paradigm and a more efficient hardware design than its predecessors, markedly improves the reconstructed image quality. The ultrafast imaging reveals the instantaneous light scattering pattern as a photonic Mach cone. We envision that our technology will find a diverse range of applications in biomedical imaging, materials science, and physics.

We have recently reported on a method to design at will the spatial profile of transmitted coherent light after propagation through a strongly scattering sample, exploiting wavefront shaping in combination with a transmission matrix approach. In this paper, we explore experimentally and theoretically the ability of this approach to generate foci whose full width at half maximum are smaller than the diffraction-limited speckle grain size, using (Bessels) beam variations implemented with virtual annular filters.

Light propagation in a turbid medium is typically considered for flat or regular surfaces. However, such an approximation often does not reflect an experimental reality, and, in this report, we attempt to optimize the surface of a scattering medium to improve the optical coupling into the medium. By making conical microchannels in a turbid medium using short-pulsed laser micro-drilling, we show that we were able to substantially increase the photon life-time and diffusion radius in the medium.

Slow light, i.e., the delay of an incident resonant pulse, can be observed in the throughput of an optical whisperinggallery microresonator. It can be produced by a single overcoupled whispering-gallery mode (WGM), or, more usefully, through induced transparency effects that are observed in the case of two coresonant WGMs with very different quality factors. There are several different methods for achieving induced transparency, two of which will be considered here. In addition, under the right conditions, light in a WGM can excite acoustic WGMs by forward Brillouin scattering. This nonlinear process due to electrostriction has a threshold, above which energy is transferred from the first optical WGM to the acoustic WGM and to a lower-frequency optical WGM. When one of the optical WGMs taking part in this optomechanical process is also involved in the production of slow light, the pulse delay can be affected. Analytical expressions for pulse delay in the three cases mentioned above are examined in terms of the WGM intracavity powers and it is shown that when the higher-frequency optical WGM is responsible for slow light, the pulse delay is reduced when the optomechanical process occurs. This conclusion is verified by a numerical model.

An analysis is presented of k-space coupling of energy from an object into one or more proximal resonant scatterers. The choice of basis function provides insight into coupling mechanisms and efficiency which leads to the design of effective resonant scatterers that can direct energy and/or information associated with high-k evanescent fields away from the object. We discuss the trade-offs between the k-space and ω-space coupling as a function of the Q of the resonant scatterer. At the nanoscale, this has applications for super-Planckian heat removal as well as superresolution imaging.

We investigate the ability to focus the laser beam (λ=0.65μm) propagated through the scattering suspension of polystyrene microspheres in distilled water by means of bimorph deformable mirror. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, while the CCD camera was used to measure the intensity of the focal spot in the farfield. Bimorph deformable mirror with 14 electrodes was applied in order to increase the intensity of the focal spot in the far-field. We investigated the efficiency of the laser beam focusing improvement by means of three techniques: LSQ fiterror minimization by Shack-Hartmann sensor, Hill-climbing optimization by Shack-Hartmann sensor and Hill-climbing optimization by far-field CCD camera.

The study of photon migration through highly scattering media opens the way to the non-invasive investigation of biological tissues well below the skin surface. When the medium is addressed in reflectance geometry, a key issue is to maximize the depth reached by migrating photons. By exploiting the Diffusion Approximation of the Radiative Transfer Equation, we calculated the time-resolved and continuous-wave probability density functions for the maximum depth reached by detected photons, for both a homogeneous and a layered laterally-infinite diffusive slab. From the probability density functions it is possible to calculate the mean value of the maximum depth at which detected photons have undergone scattering events.

The effective scattering Mueller matrices obtained by the simulation were simplified to the reduced matrices and factorized using the Lu–Chipman polar decomposition, which afforded the polarization parameters in two dimensions. In general, the scalar retardance around the illumination point of a pencil beam shows a broad azimuthal dependence with an offset. Photons may behave quite differently under the birefringence according to their polarization state. In contrast, when the birefringence is oriented along the y -axis in the plane parallel to the surface ( x ? y ) plane, for example, the azimuthal dependence of the scalar retardance shows clear maxima along the x - and y -axes and sharp valleys between the maxima. Photons propagating in the medium probably experience the retardance in nearly the same way when they are polarized linearly and circularly. Moreover, the polarization parameters generally become nonsymmetric with respect to the plane perpendicular to both the x - y plane and the plane containing the birefringence axis, which suggests that the pathway of the lateral propagation of photons from the illumination point to the surrounding is slightly oblique upward relative to the x - y plane. These results were also compared with the case in which the birefringence axis is perpendicular to the x - y plane.

In this study, finite-difference time-domain (FDTD) algorithm has been used to work out the cell light scattering problem. Before beginning to do the simulation contrast, finding out the changes or the differences between normal cells and abnormal cells which may be cancerous or maldevelopment is necessary. The preparation of simulation are building up the simple cell model of cell which consists of organelles, nucleus and cytoplasm and setting up the suitable precision of mesh. Meanwhile, setting up the total field scattering field source as the excitation source and far field projection analysis group is also important. Every step need to be explained by the principles of mathematic such as the numerical dispersion, perfect matched layer boundary condition and near-far field extrapolation. The consequences of simulation indicated that the position of nucleus changed will increase the back scattering intensity and the significant difference on the peak value of scattering intensity may result from the changes of the size of cytoplasm. The study may help us find out the regulations based on the simulation consequences and the regulations can be meaningful for early diagnosis of cancers.

A novel design based on near forward light scattering detection system to measure size and concentration distribution of particles in liquids is reported. According to theory of Mie scattering, the influence of relative refractive index, particles size and wavelength on the detection results are discussed. A green optical fiber laser with 532nm was used as the excited light source. As a key part in the detection system, the focusing system using a lens structure to confine light sensitive area with Gauss distribution less than 80 μm 2 . The lateral size of the sample cell is limited to 100μm. In order to measure the particles in non-overlapping state and improve the accuracy and repeatability, a novel structure in the sample cell was used and particle velocity through the sample cell was controlled by high precision stepper motor control system of micro circulation pump. Particle light scattering signal acquisition was completed by the poly lens combination system, according to the receiving angle relative to the measured particle, which can adjust the light scattering direction to obtain better particles light scattering signal. Photoelectric signal conversion, amplification and acquisition are all the devices with high precision. The measurement results showed that the measurement system was accurate and stable when the particles size in the range of 0.5-5μm.

The cooperative excitation and absorption of light into three cavity modes (pump, Stokes and anti-Stokes), stimulated by excited radiators, is studied as bound entangled states of the photon subsystem. The three modes collective Roman emission and its connection with entangled state is defined introducing the cooperative description between photons of cavity modes. In the case, when the scattering rates in the Stokes and anti-Stokes modes coincide, the SU(2) and SU(1,1) symmetries are applied for a simple description of these cooperative processes. The possibilities to realize this effect in the free space is proposed, replacing the cavity modes with dipole active excited atoms in tow-quantum interaction with dipole-forbidden transitions of D atom. The statistical properties and detection method are proposed using the information entropy and atomic correlation functions.

The principle of microscopic scattering dark-field imaging is adopted in surface defects evaluation system (SDES) for large fine optics. However, since defects are of micron or submicron scale, scattering imaging cannot be described simply by geometrical imaging. In this paper, the simulation model of the electromagnetic field in defect scattering imaging is established on the basis of Finite-Difference Time-Domain (FDTD) method to study the scattering imaging properties of rectangular and triangular defects with different sizes by simulation. The criterion board with scribed lines and dots on it is used to carry out experiments scattering imaging and obtain grayscale value distributions of scattering dark-field images of scribed lines. The experiment results are in good agreement with the simulation results. Based on the above analysis, defect width extraction width is preliminary discussed. Findings in this paper could provide theoretical references for defect calibration in optical fabrication and inspection.

Angle-resolved Mueller matrix element from unpolarized light scattering by micro-bubble in water is simulated using Mie scattering and discrete dipole approximation (DDA) method. This element of Mueller matrix can be used to determine the scattered light intensity to study the possibility of distinguishing the size of micro-bubble. The scattering of unpolarized light beam is simulated for three various wavelengths, 425, 625, and 825 nm. We consider the micro-bubbles sphere 1 - 10 μm with relative refractive indices to water as medium 0.75. The The result show that both Mie and DDA scattering simulation produce similar result and the result shows promising potential of using light scattering to distinguish and measure the micro-bubble sphere diameter size. Clear distinction is shown for 60 – 80 degree of detection angle.

By considering propagation equations of Stokes-waves for the Stimulated Brillouin Scattering (SBS) and the Stimulated Raman Scattering (SRS) together with propagation-rate equations of Ytterbium-doped double-clad fiber amplifiers, we numerically solve set of coupled partial differential equations and investigate dynamic characteristics of these amplifiers such as the temporal pulse energy, power, upper-level population distribution, amplified spontaneous emission, stored energy, pulse waveform evolution and the threshold of inelastic scatterings in different regimes of the temporal pulse width, input pulse peak power, input pulse bandwidth and repetition rates. Based on our analysis we establish some criteria for the threshold of inelastic scatterings according to characteristics of the input pulse and amplifying regime. Also for the first time, to the best of our knowledge, we discuss effect of the input pulse shape on the threshold of inelastic scatterings and importance of using pulse shaping methods.

Phase modulation of the signal laser into multiple laser-lines is one of the common methods to suppress the stimulated Brillouin scattering (SBS) effect in high power narrow linewidth fiber amplifiers. In order to achieve optimal effect, the multiple laser-lines should have equal amplitudes. In this paper, the phase modulation signal we employed is the sum of a finite number of sinusoidal signals with different initial phases and different weights. The stochastic parallel gradient descent (SPGD) algorithm is used to search for the optimal initial phases and weights. Through numerical simulation, we obtain homogeneous symmetrical spectra with 11, 19 and 29 lines whose mean square errors of power density are less than 3%.

The traditional laser temperature measurement usually adopt the direct detection method, while the direct detection method is easily influenced by aerosol scattering and background stray light. In this paper, the DSC710 balanced detector was first applied to the measurement of complete gas Rayleigh - Brillouin scattering spectrum (RBS). By utilizing the difference of RBS spectrum broadening under different temperature to get the temperature information. In this article, a simple theoretical derivation and error analysis has been made. The results show that using this method can effectively inhibit the interference of background stray light and has high precision.

Lidar is short for light detection and ranging, which is a tool to help measuring some useful information of atmosphere. In the recent years, more and more attention was paid to the research of wind measurement by lidar. Because the accurate wind information can be used not only in weather report, but also the safety guarantee of the airplanes. In this paper, a more detailed signal model of wind measurement lidar is proposed. It includes the laser transmitting part which describes the broadening of the spectral, the laser attenuation in the atmosphere, the backscattering signal and the detected signal. A Voigt profile is used to describe the broadening of the transmitting laser spectral, which is the most common situation that is the convolution of different broadening line shapes. The laser attenuation includes scattering and absorption. We use a Rayleigh scattering model and partially-Correlated quadratic-Velocity-Dependent Hard-Collision (pCqSDHC) model to describe the molecule scattering and absorption. When calculate the particles scattering and absorption, the Gaussian particles model is used to describe the shape of particles. Because of the Doppler Effect occurred between the laser and atmosphere, the wind velocity can be calculated by the backscattering signal. Then, a two parameter Weibull distribution is used to describe the wind filed, so that we can use it to do the future work. After all the description, the signal model of coherent wind measurement lidar is decided. And some of the simulation is given by MATLAB. This signal model can describe the system more accurate and more detailed, so that the following work will be easier and more efficient.

An analytical formula model which is used to describe laser beam’s depolarization characteristics is solved based on multiple Rayleigh scattering model. Firstly, by using Stokes vector to characterize intensity and polarization, while at the same time using Mueller matrix and rotation matrix to characterize polarization changing in scattering procedure, a single scattering model is built. Then, a multiple scattering model is built considering the effects of atmospheric absorbing and scattering attenuation. The received light’s Stokes vectors through multiple scattering procedure are separately solved. At last, on the basis of multiple scattering vectors, the depolarization characteristics of laser beam propagation through atmosphere are estimated though calculating ratio of depolarization and polarized angle shifting. The numerical analysis based on analytical conclusion of this paper shows that for a horizontal polarized laser beam, its ratio of depolarization is about 1% and polarized angle shifting is about 0.3。 when propagates through atmosphere and arrives into the receiver on the ground, and both the above characteristics have only a small change compared with the change of cloud’s depth. The findings of these research show that Rayleigh scattering from atmosphere has a weak effect on the laser beam’s polarization status. The multiple scattering model and Stokes vector analytical formulas raised in the paper could also be used to study the depolarization characteristics of ellipse polarized laser beam and partially polarized laser beam propagating through atmosphere. The research findings of this paper will have theoretical guiding significances in the domain of laser communication, laser detection and laser imaging.

Accurate measurement of Rayleigh scattering is crucially important for fundamental understanding of the plasmonic properties of meltimeric (≥ 3) nanoparticles that can be served as efficient SERS sensing platforms and nanophotonic materials. Thus, using the laser-scanning assisted dark-field microscopy that enabled to precisely collect far-field (Rayleigh) scattering from the centers of individual trimeric nanoparticles, we monitored spectral redistributions of oscillating coupled plasmonic modes as a function of trimer symmetry. As a consequence of the precise measurement of the polarization-resolved Rayleigh scattering spectra obtained from triangular trimers to linear trimers via elongated triangular trimers, the in-phase horizontally oscillating plasmonic mode with the largest dipole moment is found to be greatly increased by 20-folds, whereas the axially oscillating plasmonic mode with the second-largest dipole moment is dramatically decreased by 70-folds. Consequently, the overall quantity of the far-field scattering, the total sum of the individual coupled plasmonic modes, was gradually increased by 2-folds. The precise polarization-resolved Rayleigh scattering measurement also visualizes directly the directions of the radiation fields of individual oscillating coupled plasmonic modes, which would be valuable information in systematic controlling the polarization direction of the scattered light from the trimers. Overall, we showed an exemplary quantitative and extensive study of the coupled plasmonic modes from nanoparticles, giving a simple but clear insight.

Statistics of the random phase screens used for the modeling of beam propagation and imaging through the turbulent atmosphere is currently based on the Markov Approximation (MA) for wave propagation. This includes the phase structure functions of individual screens and the use of the statistically-independent screens for the multi-screen splitstep simulation of wave propagation. As the propagation modeling progresses to address the deep turbulence conditions, the increased number of phase screens is required to accurately describe the multiple scattering. This makes the MA a critical limitation, both because phase statistic of the thin turbulent layer does not follow MA, and because the closely space screens cannot be considered as statistically and functionally independent. A recently introduced Sparse-Spectrum (SS) model of statistically homogeneous random fields makes it possible to generate 3-D samples of refractive-index fluctuations with prescribed spectral density at a very reasonable computational cost. This leads to generation of samples of the phase screen sets that are free from the limitations of the MA. We investigated statistics of the individual phase screens and cross-correlations between the pairs of phase screens and found that the thickness Δz of the turbulent layer replaced by the phase screen is a new parameter defining the phase statistics in the non-Markov case. SS-based numerical algorithms for generation of the 3-D samples of the turbulent refractive index, and for the phase screen sets are presented. We also compare the split-step simulation results for the traditional MA and non-Markov screens.

Based on the range-gated technology in the application of airborne laser detection imaging system, sequence relations of the parameters in the model of range gating in detail was analyzed. The effective scope of atmospheric backscatter and the moment before or after pulsing of the unit section was obtained. Horizontal range-gated imaging model was established and the calculation method of backscattered light intensity was given. Then slant distance detection of airborne laser active imaging was revised. By the object-image relation of points on the scattering section, the light path diagram of imaging detection system was built and the corresponding relation of light intensity between scattering points and receiving points was given. The variation regularity and distribution of light intensity on the detector under horizontal and slant detection were gained. Under the idea, the outfield testing platform was set up, and the relative error of data between measured and simulated results was controlled within 5%. The two kinds of data achieved a good coincident, which demonstrated the effectiveness of the built model. The two kinds of data achieved a good coincident, which demonstrated the effectiveness of the built model.

Range-gated active imaging is a well-known technique used for night vision or for vision enhancement in scattering environments. The elimination of the backscattering effects leads to a significant increase in the vision range in scattering environments. Surprisingly, even if a lot of authors estimate that active imaging brings a gain in range when used in scattering environments, there are no studies which systematically investigate and quantify the real gain provided by range gating in comparison with classical imaging systems and in different controlled obscurant densities. In this paper, we thoroughly examined the performance enhancement of laser range gating in comparison with a color camera representing the human vision. On the one hand, we studied the influence of different types of obscurants and showed that the type of obscurant leads to very different results. On the other hand, we examined the influence of different technical parameters on the laser side and on the camera side. The influence of range gating and of the gate shape was studied. These experiments led us to conclude that it is necessary to combine a short laser pulse with a short camera integration time to acquire contrasted images in dense scattering media.