Optical Heterodyne Polarimeter for Studying Space-and Time-dependent State of Polarization of Light

Abstract

This paper describes an optical heterodyne polarimeter with a photodetector array by which the space- and time-dependent state of polarization (SOP) of light can be determined. Since no optical components for polarization control are used, the time response of the polarimeter is free from such components, but is basically limited to the frequency bandwidth of the photodetector array used. The signal and local oscillator beams are coherently photomixed to generate a beat photocurrent at every pixel of the photodetector array. The orthogonal linearly polarized two-frequency components of the local oscillator beam are superimposed with their respective counterpart orthogonally decomposed components of the elliptically polarized signal beam. The generated beat-photocurrent offers the significant physical parameters required for the determination of the space- and time-dependent SOP. The performance principle of the polarimeter is explained and confirmed experimentally.     

Novel Polarimetric Technique Exploring Spatiotemporal Birefringent Response of an Anti-ferroelectric Liquid Crystal Cell

Abstract

This paper describes a novel polarimetric technique for mapping the spatiotemporal birefringent parameters characterizing an anti-ferroelectric liquid crystal cell. A linearly polarized beam of light transmitted by the liquid crystal cell turns into an elliptically polarized beam. Some birefringent irregularities existing over the cell make state of polarization of the elliptically polarized beam of light be spatiotemporal. This beam works as a signal beam to interfere with a reference beam consisting of two orthogonal linearly polarized components. The resultant interference pattern is taken by a charge-coupled device video camera and recorded in a computer. The computer gives the information required for determining the spatiotemporal birefringent parameters that characterize the liquid crystal cell. The major advantage is that the two-dimensional distribution of the birefringent axes as well as the two principal refractive indices can be determined simultaneously, and no use of any optical components for polarization alignment makes it possible to follow a rapid change in birefringent parameters within the maximum frame rate of the video camera. A change in time-dependent birefringent parameter is measured at every 0·1 ms for the demonstration experiment.     

Two-dimensional polarization encoding with a phase-only liquid-crystal spatial light modulator

We show how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM). Each pixel of the LCSLM acts as a voltage-controlled wave plate and can be programmed over a 2pi phase range at a wavelength of 514.5 nm. Techniques are reviewed for either rotating the major axis of elliptically polarized light or for converting an input linearly polarized beam into an arbitrary elliptically polarized beam. Experimental results are demonstrated in which we generate various two-dimensional spatial patterns of polarized light. Several potential applications are suggested. We also report an unexpected edge-enhancement effect that might be useful in image processing applications.     

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.     

Polarization state fixer composed of passive optical devices

We investigate a polarization state fixer that produces light with an arbitrary desired polarization state and constant power from an arbitrary elliptically polarized input light whose principal polarization axis fluctuates randomly. An example of such a device composed of a quarter-wave plate and a polarizer is proposed, and its characteristics at wavelengths of 633 nm and 1550 nm are demonstrated. We conclude that we cannot obtain a passive device that produces fixed-axis, linearly polarized light with a constant power level from an elliptically polarized light with a varying elliptical parameter.     

Statistical properties of a radially polarized twisted Gaussian Schell-model beam in a uniaxial crystal

We derive the analytical formulas for the elements of the cross-spectral density matrix of a radially polarized partially coherent beam with a twist phase named radially polarized twisted Gaussian Schell-model (RPTGSM) beam propagating in a uniaxial crystal, and explore the statistical properties, such as the intensity distribution, the degree of polarization (DOP) and the state of polarization (SOP) of such beam in a uniaxial crystal with the help of the derived formulas. It is found that the statistical properties of a RPTGSM beam are closely related with the twist phase and the anisotropy of the uniaxial crystal, e.g. the twist phase leads to the rotation of the intensity, DOP and SOP distributions, and the anisotropy of the uniaxial crystal leads to the asymmetry distributions of these statistical properties. Our results will be useful for designing light field with prescribed intensity, DOP and SOP distributions, and may be useful in optical manipulations and free-space optical communications.     

Extremely narrowed spontaneous emission spectrum induced by elliptically polarized light

Abstract

We demonstrate the control of spontaneous emission from a five-level atom embedded in a modified reservoir under the action of a single control beam with elliptical polarization. For different initial-state preparations, we take into account the influence of the phase difference between the two circularly polarized components of the control beam on the behavior of spontaneous emission. For the ground initial states, the spontaneous emission spectrum usually shows ultranarrow central lines which are greatly enhanced. In contrast, for the excited initial states, these enhanced ultranarrow lines are significantly suppressed due to the destructive quantum interference. Furthermore, our numerical simulations indicate that the multipeak structure appears in the presence of the elliptically polarized control beam and external magnetic field. Such a scheme for controlling spontaneous emission may find applications in high-precision spectroscopy.     

Real-time objects recognition by photoanisotropic copies

The method of object recognition is described by the example of objects of amplitude transparent type. The method is to obtain a photoanisotropic copy of object images on polarization-sensitive material. At consequent illumination of the photoanisotropic copy with a parallel circularly polarized beam of nonactinic light, the transmitted light becomes elliptically polarized. It is shown that the characteristics of the summary polarization ellipse in the Fraunhofer diffraction region uniquely identify the given object. The real-time determination of the characteristics of the summary polarization ellipse is made by means of diffraction gratings of anisotropic profile and by comparison of these characteristics with etalon from the database.     

Optical method for measuring optical rotation angle and refractive index of chiral solution

Based on the phenomena of Brewster's angle and the principles of common-path heterodyne interferometry, we present an optical method for measuring the optical rotation angle and the refractive index of a chiral solution simultaneously in one optical configuration. A heterodyne light beam and a circularly polarized heterodyne light beam are separately guided to project onto the interface of a semicircle glass and a chiral solution. One of the beams is transmitted through the solution, and the other is reflected near Brewster's angle at the interface. Then the two beams pass through polarization components respectively for interference. The phase differences of the two interference signals used to determine the rotation angle and the refractive index become very high with the proper azimuth angles of some polarization components, hence achieving an accurate rotational angle and a refractive index. The feasibility of the measuring method was demonstrated by our experimental results. This method should bear the merits of high accuracy, short sample medium length, and simpler operational endeavor.     

Optically switchable and axially symmetric half-wave plate based on photoaligned liquid crystal films

We demonstrate an optically switchable half-wave plate (HWP) composed of a photoaligned and axially symmetric liquid crystal (ASLC) film containing two azobenzene derivatives, methyl red (MR) and 4-butyl-4′-methoxyazobenzene (BMAB). MR is responsible for photoalignment, and BMAB is used for optical tuning and switching the state of polarization (SOP) of probe beam (633 nm He–Ne laser) passing through the MR/BMAB doped ASLC film. The photoaligned ASLC film is first fabricated using a line-shaped laser beam (532 nm) exposure applied on a rotating LC sample. The fabricated ASLC film can passively change the linearly polarized light. Under UV light exposure, the formation of cis-BMAB (bend-like shape) within the film disrupts the LC molecules, switches the LC orientation, and further changes the SOP of the probe beam. Under laser irradiation (532 nm), the formation of trans-BMAB (rod-like shape) reverts the LC orientation back and simultaneously generates cis-MR, helping anchor the LC in the previously photoaligned orientation. The photoaligned MR/BMAB-doped LC HWP can change the linear SOP under alternating UV and visible light exposure.     

对地遥感中的光谱偏振探测方法研究

简要分析了遥感偏振民现行的遥感强度探测在物理含义方面的区别,并 举例说明了偏振遥感信息在表达暗目标（或低照度）和人工建筑目标方面有更丰富的内涵。从物理数学方法上简要归纳了遥感偏振信息的处理解译过程。给出了一种航空光谱偏振CCD相机的主要技术指标设计,并与法国的POLDER偏振仪进行了类比。     

The design and performance of the FNAL high-energy polarized-beam facility

A new polarized-proton and -antiproton beam with 185 GeV/c momentum has been built at Fermilab. The design uses the parity-nonconserving decays of lambda and antilambda hyperons to produce polarized protons and antiprotons, respectively, a beam-transport system that minimizes depolarization effects, and a set of twelve dipole magnets that rotate the beam-particle spin direction. A beam-tagging system determines the momentum and polarization of individual beam particles. This allows a selection of particles in definite intervals of momentum and polarization. Measurements performed by two different polarimeters showed that the beam is polarized and the determination of polarization by beam-particle tagging is verified. A new measurement of the analyzing power of large-x_F π⁰ production may lead to another beam polarimeter.     

The Sénarmont Compensator: An Early Application of the Geometric Phase

Abstract

The Sénarmont compensator has been used for many years to measure the phase retardation between the two components of an elliptically polarized beam of light. This letter shows how the operation of this device actually makes use of the geometric phase.     

Interaction of Counter-propagating Elliptically Polarized Light Waves in Isotropic Nonlinear Media

Abstract

The nonlinear interaction of elliptically polarized counter-propagating waves in an isotropic transparent medium is analysed. Self-induced changes in the polarization of the counter-propagating light waves, are described. Using these results, a new type of modulator giving self-induced rotation of the polarization ellipse (SIRPE) is studied. The transmission of counter-propagating waves in the SIRPE modulator is shown to exhibit saturation with increase in light intensity and to be a multiple-valued function of the light intensity.     

Optical Transmission in Polycrystals

Optical transmission in a polycrystalline aggregate consisting of randomly oriented anisotropic transparent crystals has been worked using Mueller matrices. The interesting results are: (1) A completely polarized beam of light emerges as partially polarized light. (2) The completely polarized part of the emergent beam is in the same state of polarization as the incident light for optically inactive crystallites. (3) The intensity of the completely polarized part not only depends on the optical and the geometrical parameters of the crystallite but also on the polarization state of the incident light. (4) For optically active crystallites the medium behaves as an isotropic optically active solid with a rotatory power equal to the mean rotatory power of the single crystal. This helps one in extracting most of the gyration tensor components in enantiomorphic optically active crystals.     

Solitary Waves of Maxwell's Equations in Nonlinear Anisotropic Media

Abstract

The (1 + 1)-D solitary wave solutions of Maxwell's equations in nonlinearity induced anisotropic media (in liquids such as carbon disulphide, and in crystals, etc.) are investigated. We find that there is no arbitrarily linearly polarized (in the x-y plane perpendicular to the propagation direction z) soliton solution from Maxwell's equations except that with linear polarization either in alignment with or orthogonal to the geometric axis of the light induced refractive index change. This contradicts the prediction of the vector nonlinear Schroedinger equation (an approximation of Maxwell's equations) which yields soliton solutions with an arbitrary linear polarization. However, Maxwell's equations are found to admit stable elliptically polarized solitary wave solutions which reduce to the stable circularly polarized solitary wave solutions of the vector nonlinear Schroedinger equation when the induced refractive index change approaches zero.     

Polarization and retinal image quality estimates in the human eye

We have previously studied how polarization affects the double-pass estimates of the retinal image quality by using an imaging polarimeter [Opt. Lett. 24, 64 (1999)]. A series of 16 images for independent combinations of polarization states in the polarimeter were recorded to obtain the spatially resolved Mueller matrices of the eye. From these matrices, double-pass images of a point source for light with different combinations of incoming (first-pass) and outcoming (second-pass) polarization states were reconstructed and their corresponding modulation transfer functions were calculated. We found that the retinal image or, alternatively, the ocular aberrations, are nearly independent of the state of polarization of the incident light (in the first pass). This means that a significant improvement in the ocular optics by using a specific type of polarized light could not be achieved. However, quite different estimates of the retinal image quality are obtained for combinations of polarization states in both the first and the second passes in the double-pass apparatus.     

小型机载偏振成像系统研制及应用研究

机载偏振成像是未来遥感探测领域的重要研究方向之一。首先基于液晶双折射率效应完成了高精度液晶偏振控制器研制,并对其偏振调制精度进行标定;然后利用液晶偏振控制器搭建了高精度小型机载偏振成像系统,并基于小型固定翼无人机完成了系统的搭载飞行测试和目标识别探测试验。试验结果表明,液晶偏振控制器的Stokes偏振参数调制精度优于98%,利用液晶偏振控制器搭建的小型机载偏振成像系统可有效抑制背景干扰,提高低对比度目标的轮廓提取能力和目标识别能力。研究成果为偏振成像技术在目标侦察、环境监测、农作物普查等方面的应用提供了一种有效的技术途径。     

A proton and neutron beam polarimeter at SATURNE II

A beam polarimeter using CH₂ and carbon targets has been used to measure proton and neutron beam polarization in the energy range 0.4–2.8 GeV in one of the beam lines at the SATURNE II accelerator. The analyzing power for np-scattering is calibrated against the known analyzing power for pp-scattering by using the polarized deuteron beam to measure simultaneously the asymmetries for scattering of quasifree protons and neutrons in the deuterons. A low level of systematic errors is achieved by pulse to pulse polarization reversal at the ion source of the accelerator, and by measuring left and right scattering simultaneously. The detailed operation procedure and the beam polarizations measured during all experiments from 1981 to 1984 are presented.