Dielectric tensor measurement from a single Mueller matrix image

A technique for measuring dielectric tensors in anisotropic layered structures, such as thin films of biaxial materials, is demonstrated. The ellipsometric data are collected in a quasi-monochromatic Mueller matrix image acquired over a large range of incident and azimuthal angles by illuminating a very small area on the sample with a focused beam from a modulating polarization state generator. After the beam interacts with the sample, the reflected and/or transmitted light is collected using an imaging polarization state analyzer. An image of the exit pupil of a collection objective lens is formed across a CCD such that each pixel collects light from a different angle incident on the sample, thus acquiring ellipsometric data at numerous incident angles simultaneously. The large range of angles and orientations is necessary to accurately determine dielectric tensors. The small but significant polarization aberrations of the low-polarization objective lenses used to create and collect the focused beams provide a significant challenge to accurate measurement. Measurements are presented of a thin-film E-type polarizer and a stretched plastic biaxial film.     

Self-Assembled Tetratic Crystals by Orthogonal Colloidal Force

Bonding simple building blocks to create crystalline materials with design has been sophisticated in the molecular world, but this is still very challenging for anisotropic nanoparticles or colloids, because the particle arrangements, including position and orientation, cannot be manipulated as expected. Here biconcave polystyrene (PS) discs to present a shape self-recognition route are used, which can control both the position and orientation of particles during self-assembly by directional colloidal forces. An unusual but very challenging two-dimensional (2D) open superstructure—tetratic crystal (TC)—is achieved. The optical properties of the 2D TCs are studied by the finite difference time domain method, showing that the PS/Ag binary TC can be used to modulate the polarization state of the incident light, for example, converting the linearly polarized light into left-handed or right-handed circularly polarized light. This work paves an important way for self-assembling many unprecedented crystalline materials.     

Dependence of the tracking performance of an optical disk on the direction of the incident-light polarization

In optical-disk data-storage systems, the signal that provides tracking information is dependent on the groove shape, the optical constants of the materials involved, and the polarization state of the incident light. In this paper, we show that the tracking signal can be described by two measurable quantities, both of which are largely independent of aberrations in the optical system. Using these two quantities, we match the tracking performance of a given disk to an equivalent disk having rectangular grooves-the adjustable parameters being the rectangular groove depth and the duty cycle. By assumption, these rectangular grooves modulate only the phase of the incident beam and disregard its state of polarization. The effective groove depth and the duty cycle thus become dependent on the polarization state of the incident beam. We examine these dependences for various disks having different groove geometries and different combinations of materials.     

Mechanism and symmetry properties of depolarization in weak scattering of light

The mechanism and some symmetry properties of depolarization upon weak scattering of light from a class of random media were studied theoretically. Departing from the angular distribution of the degree of polarization, our derivations showed the mechanism that induces the change of polarization can be split into two parts of different nature. One is the vectorial effect that redistributes the original light components, and the other is the interaction effect of the medium that modulates the correlation properties of the incident field. We also showed that there is dependence of the angular distribution on the incident polarization state; i.e., the angular pattern and its symmetry depend on both the orientation and ellipticity of the incident polarization. Random light was analyzed in the space-frequency domain.     

利用WDM光纤耦合器的光纤光栅传感解调技术

根据 WDM 光纤耦合器波长解调方案的工作原理、偏振特性以及影响系统波长分辨力的因素,提出一种改进的利用 WDM 光纤耦合器的光纤光栅传感解调技术。该技术在原技术的基础上,采用偏振控制器控制入射光偏振状态,提高了解调的精度和稳定性。对 WDM 光纤耦合器的多次波长扫描结果表明,采用偏振控制器后,其波长误差可减小到 5pm 左右。实验采用 1540/1560nm的 WDM 光纤耦合器对单点光纤光栅应变传感器进行静态解调,结果表明:按此技术开发的解调系统具有 0.01nm 波长分辨力和 10nm 的波长线性解调范围。     

Fiber-based polarization-sensitive Mueller matrix optical coherence tomography with continuous source polarization modulation

We report on a new configuration of fiber-based polarization-sensitive Mueller matrix optical coherence tomography that permits the acquisition of the round-trip Jones matrix of a biological sample using only one light source and a single depth scan. In this new configuration, a polarization modulator is used in the source arm to continuously modulate the incident polarization state for both the reference and the sample arms. The Jones matrix of the sample can be calculated from the two frequency terms in the two detection channels. The first term is modulated by the carrier frequency, which is determined by the longitudinal scanning mechanism, whereas the other term is modulated by the beat frequency between the carrier frequency and the second harmonic of the modulation frequency of the polarization modulator. One important feature of this system is that, for the first time to our knowledge, the Jones matrix of the sample can be calculated with a single detection channel and a single measurement when diattenuation is negligible. The system was successfully tested by imaging both standard polarization elements and biological samples.     

多角度动态光散射法的纳米颗粒精确测量

基于动态光散射原理,采用自主研发的多角度动态光散射装置,对纳米及亚微米颗粒粒径准确测量方法进行了探究。自研装置采用带有光阑组的精密入射光路设计,以及匹配液池及Beam-stop设计,极大提高了信噪比;同时避免了测量角度的互补方向上,由于样品池与空气界面折射率不同导致的反射光信号对有效信号的干扰。在此基础上,对不同浓度、粒径的聚苯乙烯(PS)颗粒溶液进行了测定及不确定度分析。结果表明,对同一粒径的PS颗粒,增加颗粒浓度时,多重散射首先发生于大、小测量角度,越接近90°,发生多重散射的浓度越高;随着粒径增大,受不可忽略的颗粒间相互作用的影响,粒径测量结果表现出了强烈的角度依赖性,甚至波动性。     

All-optical controlling of the focal intensity of a liquid crystal polymer microlens array

The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an all-optically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.     

Secure optical memory system with polarization encryption

A novel secure holographic memory system with polarization encoding is proposed. Two-dimensional original data are encoded as a two-dimensional polarization distribution. The polarization state at each pixel is scrambled by a mask that changes the polarization state into a random state. The mask can rotate the direction of the principal axes of the elliptically polarized light and can change the phase retardation at each pixel. The light with the random polarization state is stored as a hologram that can produce the vector phase-conjugate beam. In the decryption the vector phase-conjugation readout can recover the original polarization state by use of the same mask used in the encryption. Experimental results of encryption and decryption with a bacteriorhodopsin film are presented.     

Scattering-induced changes in the degree of polarization of a stochastic electromagnetic plane-wave pulse

The scattering of a stochastic electromagnetic plane-wave pulse on a deterministic spherical medium is investigated. An analytical formula for the degree of polarization (DOP) of the scattered field in the far zone is derived. Letting pulse duration T(0) → ∞, our formula can be applied to study the scattering of a stationary stochastic electromagnetic light wave. Numerical results show that the DOP of the far zone field is closely determined by the size of the spherical medium when the incident field is a stochastic electromagnetic plane-wave pulse. This is much different from the case when the incident field is a stationary stochastic electromagnetic light wave, where the DOP of the far zone field is independent of the size of the medium. One may obtain the information of the spherical medium by measuring the scattering-induced changes in the DOP of a stochastic electromagnetic plane-wave pulse.     

Expanded beam (macro-imaging) ellipsometry

Our aim was to make possible to use spectroscopic ellipsometry for mapping purposes during one measuring cycle (minimum one rotation period of polarizer or analyzer) on many sample points. Our new technique uses non-collimated (non-parallel, mostly diffuse) illumination with an angle of incidence sensitive pinhole camera detector system and it works as an unusual kind of imaging ellipsometry. Adding multicolour supplemets, it provides spectral (a few wavelengths on a 2D image or a full spectrum along a line) information from rapid measurements of many points on a large (several dm2) area. This technique can be expanded by upscaling the geometry (upscaling the dimensions of the instrument, and characteristic imaging parameters such as focal lengths, distances, etc.). The lateral resolution is limited by the minimum resolved-angle determined by the detector system, mainly by the diameter of the pinhole. (The diameter of the pinhole is a compromise between the light intensity and the lateral resolution.) Small-aperture (25 mm diameter) polarizers are incorporated into both the polarization state generator (PSG) and polarization state detection (PSD) components of the instrument.The detection is almost without background because the pinhole serves as a filter against the scattered light. One rapid measuring cycle (less than 10 s) is enough to determine the polarization state at all the points inside the illuminated area. The collected data can be processed very fast (seconds) providing nearly real-time thicknesses and/or refractive index maps over many points of the sample surface even in the case of multilayer samples. The speed of the measuring system makes it suitable for using even on production lines. The necessary (in each sample-point different) angle-of-incidence and the mirror-effect calibration are made via well-known and optimized structures such as silicon/silicon-dioxide samples. The precision is suitable for detecting sub-nanometer thickness and a refractive index change of 0.01.The method can be used for mapping and quality control in the case of large area solar cell table production lines even in a vacuum chamber with 5-10 mm lateral resolution.     

Polarization-preserving angular shifter

This study shows that by using a wedge plate the incident direction of light propagation can be rotated as desired while still preserving beam polarization. This study also deduces the basic condition of this preservation of polarization. Two typical wedge plates are analyzed for numerical demonstration. Simulation results verify that a collimated beam with a +45 degrees linear polarization can be guided to an expected direction while preserving the state of polarization with a square of the variation of the ellipse ratio of less than 0.0001%. This study also numerically shows that the wedge vertex angle is the most critical issue and that approximately 0.1 degrees accuracy is required to preserve the polarization state.     

C/C复合材料的旋转偏振成像方法

本研究提出了一种旋转偏振显微成像方法。根据热解碳独特的双反射特性,设计了仅有一个检偏镜的显微图像采集系统;通过检偏镜的旋转,获取C/C复合材料在不同偏振角位置的单偏光图像;经过图像配准和图像融合,合成最大、最小反射率和双反射率映射图像。这种映射图像反映的信息是采用常规显微镜法不能观察到的,它直观地揭示了材料内部的微观结构特征,可以作为测定热解碳真实反射率的基础。本研究可为C/C复合材料微观结构分析以及相关特征参数测量提供理论依据和实现途径。     

Fiber-based single-channel polarization-sensitive spectral interferometry

We present a novel, to our knowledge, fiber-based single-channel polarization-sensitive spectral interferometry system that provides depth-resolved measurement of polarization transformations of light reflected from a sample. Algebraic expressions for the Stokes parameters at the output of the interferometer are derived for light reflected from a birefringent sample by using the cross-spectral density function. By insertion of a fiber-optic spectral polarimetry instrument into the detection path of a common-path spectral interferometer, the full set of Stokes parameters of light reflected from a sample can be obtained with a single optical frequency scan. The methodology requires neither polarization-control components nor prior knowledge of the polarization state of light incident on the sample. The fiber-based single-channel polarization-sensitive spectral interferometer and analysis are demonstrated by measurement of phase retardation and fast-axis angle of a birefringent mica plate.     

智能化激光显示系统的设计与研究

研制了一套由激光器,图形输入仪,控制计算机,驱动器,光学工作台及大屏幕等六个部分构成的激光显示系统。理论研究得出,大屏幕所显示图形上的任意点P,均存在一与之对应的振镜偏转角确定值,精确控制振镜的偏转角即可扫描到P点。实验表明,系统可成功实现诸如函数图形、光栅衍射图案、光网光柱及文字动画等多功能智能化激光视频图像的动态输出。     

Degree of polarization as a criterion to obtain the nine bilinear constraints between the Mueller-Jones matrix elements

The degree of polarization is employed as a criterion to find the nine independent relations among the elements of the Mueller-Jones matrix. This procedure is applied by considering a previously determined, physically realizable Mueller matrix. On the other hand, the nine bilinear constrains are obtained by directly measuring the degree of polarization from an outgoing beam of light from an optical system by considering nine incident states of light taken from the Poincaré sphere. For practical purposes, all the incident polarization states must be scanned from the Poincaré sphere in order to satisfy the over-polarization and the over-gain conditions, respectively, for the physical realizability of the Mueller matrix.     

Spatial light modulators for high-brightness projection displays

We fabricated polymer-dispersed liquid-crystal light valves (PDLCLV's) consisting of a 30-mum-thick hydrogenated amorphous-silicon film and a 10-mum-thick polymer-dispersed liquid-crystal (PDLC) film composed of nematic liquid-crystal (LC) microdroplets surrounded by polymer. The device can modulate high-power reading light, because the PDLC becomes transparent or opalescent independent of the polarization state of the reading light when either sufficient or no writing light is incident on the PDLCLV. This device has a limiting resolution of 50 lp/mm (lp indicates line pairs), a reading light efficiency of 60%, a ratio of intensity of light incident on the PDLC layer to intensity of light radiated from the layer, and an extinction ratio of 130:1. The optically addressed video projection system with three PDLCLV's, LC panels of 1048 x 480 pixels as input image sources, a 1-kW Xe lamp, and a schlieren optical system projected television (TV) pictures of 600 and 450 TV lines in the horizontal and the vertical directions on a screen with a diagonal length of 100 in. The total output flux of this system was 1500 lm.     

Monte Carlo and Multicomponent Approximation Methods for Vector Radiative Transfer by use of Effective Mueller Matrix Calculations

For single scattering in a turbid medium, the Mueller matrix is the 4 x 4 matrix that multiplies the incident Stokes vector to yield the scattered Stokes vector. This matrix contains all the information that can be obtained from an elastic-scattering system. We have extended this concept to the multiple-scattering domain where we can define an effective Mueller matrix that, when operating on any incident state of light, will yield the output state. We have calculated this matrix using two completely different computational methods and compared the results for several simple two-layer turbid systems separated by a dielectric interface. We have shown that both methods give reliable results and therefore can be used to accurately predict the scattering properties of turbid media.     

High-precision sizing of nanoparticles by laser transmission spectroscopy

We describe the implementation of precision laser transmission spectroscopy for sizing and counting nanoparticles in suspension. Our apparatus incorporates a tunable laser and balanced optical system that measures light transmission over a wide (210-2300 nm) wavelength range with high precision and sensitivity. Spectral inversion is employed to determine both the particle size distribution and absolute particle density. In this paper we discuss results for particles with sizes (diameters) in the range from 5 to 3000 nm. For polystyrene particles 404 to 1025 nm in size, uncertainties of ±0.5% in size and ±4% in density were obtained. For polystyrene particles from 46 to 3000 nm in size, the dynamic range of the system spans densities from ~10(3)/ml to ~10(10)/ml (5 × 10(-8) to 0.5 vol. %), implying a sensitivity 5 orders of magnitude higher than dynamic light scattering.