Dynamics of the linearly polarized fundamental Gaussian light wave

A continuous planar array of dipoles that are oriented in a particular direction and have an amplitude distribution that is Gaussian in the paraxial limit is introduced as a source for the fundamental Gaussian light wave. The radiation intensity of the Gaussian light wave is determined and its characteristics are analyzed. The universal Gaussian beam factor is deduced and identified as the radiation intensity of the scalar Gaussian wave. The total radiated power, the mean center of the localized wave, and the beam widths of the intensity distribution are obtained. The ratio of the power in the Gaussian wave to that in the corresponding paraxial Gaussian beam is used as a measure of the quality of the paraxial beam approximation. A limiting factor for the power ratio is introduced as an indicator for the acceptability of the paraxial beam approximation. The cross section and the beam widths of the localized light wave are investigated in the large and small kw0 limits, where k is the wavenumber and w0 is the beam waist at the input plane. The beam width of the full Gaussian wave is found to be less than that of the corresponding paraxial Gaussian beam both for the scalar Gaussian wave and for the Gaussian light wave.     

Magneto-optic sensor by use of time-division-multiplexed orthogonal linearly polarized light

A magneto-optic sensor is proposed and experimentally demonstrated. The sensing unit is mainly composed of an electro-optic modulator, a Faraday magneto-optic glass, and two polarizers. Different from the conventional magneto-optic sensors, this sensor utilizes a time-division-multiplexed and alternately polarized light carrier whose azimuthal angle is periodically alterable between two orthogonal linear polarization states. In particular, this sensing scheme is suitable for dc magnetic field or current measurement, and the measurement result is free from the influences of light intensity fluctuation and environmental electromagnetic interference, due to the applications of square-wave modulation and lock-in amplification techniques. The dc magnetic field in the range of +/-(0.067 approximately 20) mT has been remotely measured and the nonlinear error is less than 1.0%.     

Transmission of linearly polarized light through a single-mode fiber with random fluctuations of birefringence

A simple theoretical formalism is developed to describe the effect of transmission on linearly polarized light through a fiber with random fluctuations of birefringence. We conclude that, for any optical fiber that does not experience polarization-dependent gain or loss, there exist two orientations for linearly polarized light input into the optical fiber that will also exit the fiber linearly polarized. We report experimental results that verify this prediction and also investigate its practical implications and limitations; in particular we investigate the stability of these linearly polarized output states in laboratory conditions.     

Dispersion effects in elliptical-core highly birefringent fibers

Modal birefringence and its sensitivity to temperature and hydrostatic pressure were measured versus wavelength in three elliptical-core fibers and one fiber with stress-induced birefringence. We carried out the measurements in the spectral range from 633 to 843 nm by using interferometric methods. In fibers with elliptical cores all the measured parameters showed high chromatic dependence, whereas in fibers with stress-induced birefringence this dependence was weak. We modeled the dispersion characteristics of two elliptical-core fibers by using the modified perturbation approach first proposed by Kumar. The modification consists of introducing into the expression for the normalized propagation constants an additional perturbation term that contains information about stress-induced birefringence. The results of modeling show that the temperature and pressure sensitivity of elliptical-core fiber are associated primarily with variations in stress induced by these parameters. The agreement between measured and calculated values of sensitivity in the worst case was equal to 20% for modal birefringence and temperature sensitivity and 50% for pressure sensitivity. Lower agreement between measured and calculated values of pressure sensitivity is most probably associated with uncertainties in the material constants used in modeling.     

Three-dimensional laparoscope based on the manipulation of polarized light by a cellophane half-wave plate

A three-dimensional laparoscope that can capture three-dimensional images during surgery is reported. The principle is solely based on the manipulation of polarized light by a cellophane half-wave plate rather than computer processing; hence there is no time delay (it operates in real time) and lesions are viewed in true color, which is important for diagnostics. Three-dimensional images are obtained with a single laparoscope. A unique feature of this three-dimensional laparoscope is that it includes a virtual ruler to measure distances without physically touching the affected areas. The structure is simple, sturdy, lightweight, and its diameter is no bigger than a standard 10 mm diam laparoscope.     

Cross-polarization of linearly polarized Hermite-Gauss laser beams

Evolution of transverse intensity profiles for the dominant and cross-polarization components of linearly polarized Hermite-Gauss laser beams is studied experimentally as the beams propagate away from their waist. Measured intensity profiles and their evolution with propagation are in good agreement with the theoretical predictions.     

Shape evolution of a light pulse in a linear birefringent medium

The spreading of a three-dimensional quasi-monochromatic progressive directional wave packet (such as a laser pulse) propagating freely in a linear and transparent birefringent medium is described geometrically by means of the ellipsoid representative of the pulse's second-order moments. The medium is characterized by a second-order expansion of its dispersion relation omega(K) about the mean wave vector Km of the pulse, i.e., by its Hessian matrix (H(Km)omega), which plays two important roles. Then, for some elements of(H(Km)omega), practical expressions are provided that are related to the curvature and dispersion properties of the normal surface of the medium. Then cases in which these properties determine completely the asymptotic transverse or axial spreadings of the wave packet are specified, and the results of an experiment are discussed.     

Generation of linearly polarized transition radiation X-ray beam

We have successfully produced almost linearly polarized X-ray beam by extracting Transition Radiation (TR) X-rays through a rectangular slit 3 mrad long and 0.2 mrad wide placed downstream of a 7.5-μm thick Kapton foil stack radiator bombarded with a 1-GeV electron beam. Our calculation predicted that the linearity of TR photon was 94% for both a vertical and a horizontal slit. The measured results for the vertical slit agreed with the calculation, and the linearity of obtained TR X-ray beam was more than 90%. For the horizontal slit, the measured results differed from our expectations due to a prolonged electron beam profile. In the polarization measurement of TR photon we used the Bragg reflection on a lithium fluoride crystal [LiF(200)] which acted as both a polarimeter and a spectrometer.     

Far zone spectral shifts in light propagation from the exit face of a few-mode fibre waveguide guiding the frequency-dependent linearly polarized modes

Abstract

Far zone spectral shifts, including free space propagation of light from a planar secondary, partially coherent source represented by the exit face of a few-mode fibre waveguide, are investigated in the paraxial regime by using frequency-dependent linearly polarized (LP) modes guided by the fibre waveguide. The origin of the far zone blue or red spectral shift of individual frequency-dependent LP modes, as well as of their superposition at the particular observation point, is clarified. In particular, the dependence of the wavelength shifts of spectra on the position of the observation point in the far zone plane and the primary source linewidth is studied for the two-mode, weakly guiding, step-index fibre waveguide.     

Thermoelastic waves in a thin plate

Summary In the present work we deal with the propagation of thermoelastic waves in a thin plate occupying the Cartesian space (x ₁[–, +],x ₂[–, +],x ₃[–, +]). The analysis is based on the generalized theory of thermoelasticity proposed by Lord and Shulman modified for plane stress problems. A mathematical analysis is presented to study the wave motion characteristics of the plate and the proposed analysis is applied for the special cases of very short and very long waves.     

双折射波片相位差的精确表达

为了更准确地描述双折射波片的特性,提出了取消普遍采用的传统相位差表达式中所包含的近似假设的思想。从晶体双折射的性质出发,结合双折射波片的结构特点,将e光波法线在波片中的折射角和折射率用入射角及晶体的参量表示出来,推导出e光波法线与o光波法线间相位差更准确的表达式。为了研究偏振光之间干涉的需要,推导出光线间相位差的精确表达式,以准确表述光线的路径,特别是晶片外的路径。更精确的相位差表述为更准确地分析双折射波片的特性提供了极大的方便。     

Tight focusing of radially and azimuthally polarized vortex beams through a uniaxial birefringent crystal

Under the approximation of small birefringence, the properties of radially and azimuthally polarized vortex beams tightly focused through a uniaxial birefringent crystal are investigated. The contour plots of intensity distribution near the focus and in the real focal plane are illustrated by performing numerical calculations. The dependence of the focal shift on numerical aperture and birefringence are analyzed. Moreover, the Strehl ratio in the real focal plane as a function of birefringence is also analyzed. It is revealed that the variation of birefringence has no influence on the focal shift and the Strehl ratio of azimuthally polarized vortex beams.     

Anisotropic scattering of polarized light in a ferrofluid layer

Previously unknown effects wherein the scattering of plane-polarized light in a ferrofluid layer depends on the orientation of the electric field of the polarized radiation relative to the direction of the applied magnetic field are found experimentally, and their physical nature is explained. Pis’ma Zh. Tekh. Fiz. 23, 7–10 (September 12, 1997)     

Dispersion characteristics of magnetostatic waves propagating at a ferrite/perovskite interface

The propagation of magnetostatic waves at the interface between an yttrium-iron-garnet (YIG) film and a layer of perovskite compound LaAlO₃, SrTiO₃, or YBa₂Cu₃O_7−x (YBCO) was experimentally studied. The microwave dispersion characteristics were measured at room temperature and at 77 K. An effective method for controlling the propagation speed and the phaseshift of magnetostatic waves in the YIG/YBCO structures is suggested. Specifically, the phaseshift at 3 GHz is changed by more than 1.5π by reducing the critical current density from 1 to 0.7× 10⁶ A/cm².     

Stress-intensity factor and crack opening for a linearly viscoelastic strip with a slowly propagating central crack

The stress-intensity factor and the size of the crack opening have been calculated for a linearly viscoelastic strip with a slowly propagating central crack. The edges of the infinitely long strip are displaced normal to the crack and both clamped and shear-free strip edges have been investigated. The results are based on the solution to the problem of a suddenly loaded strip with a stationary crack. The resulting integral equation has been solved numerically for arbitrary crack length and analytical solutions in form of asymptotic series are given for crack length up to about half the strip width. The response to a propagating crack is found by superposition.This work represents part of a Ph.D. Thesis submitted to the California Institute of Technology. The author gratefully acknowledges the support of this work by the National Aeronautics and Space Administration under Research Grant NGL-05-002-005, GALCIT 120.     

Sublimation of a thin plate in a gas stream

The laminar boundary layer on a sublimating thin plate is examined.     

Femtosecond snapshot imaging of propagating light itself

An ultrafast imaging technique has been developed to visualize directly a light pulse that is propagating in a medium. The method, called femtosecond time-resolved optical polarigraphy (FTOP), senses instantaneous changes in the birefringence within the medium that are induced by the propagation of an intense light. A snapshot sequence composed of each femtosecond probing the pulse delay enables ultrafast propagation dynamics of the intense femtosecond laser pulse in the medium, such as gases and liquids, to be visualized directly. Other examples include the filamentation dynamics in CS2 liquid and the propagation dynamics in air related to the interaction with laser breakdown plasma. FTOP can also be used to extract information on the optical Kerr constant and its decay time in media. This method is useful in the monitoring of the intensity distribution in the nonlinear propagation of intense light pulses, which is a frequently studied subject in the field of physics regarding nonlinear optics and laser processing.