T-ray tomography

We demonstrate tomographic T-ray imaging, using the timing information present in terahertz (THz) pulses in a reflection geometry. THz pulses are reflected from refractive-index discontinuities inside an object, and the time delays of these pulses are used to determine the positions of the discontinuities along the propagation direction. In this fashion a tomographic image can be constructed.     

Polarization-mode dispersion measurement by an optical time-domain reflectometer with polarimetry assuming backscattering by randomly oriented nonspherical particles

In previous work on polarization-mode dispersion (PMD) measurement with an optical time-domain reflectometer with polarimetry (p-OTDR), scatterers were assumed to be a cloud of small spherical particles in a fiber. We have found that the p-OTDR waveforms were fitted well by modified Mueller matrices, assuming scattering by a cloud of nonspherical particles. We realized a PMD measurement based on the p-OTDR Jones matrix eigenanalysis (JME) method. The measured PMD was consistent with that of JME standard measurement with transmission-type polarimetry.     

T-ray computed tomography

We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.     

Characterization of T-ray binary lenses

Multilevel phase-shift Fresnel diffractive zone plates fabricated on silicon wafers have been used as T-ray imaging lenses. The imaging results, including spatial and temporal distribution of T-rays measured at the focal planes in the frequency range from 0.5 to 1.5 THz, indicate that the performance of the diffractive terahertz (THz) lens is comparable with or better than that of conventional refractive THz lenses. The unique properties of the T-ray binary lens make it possible to fabricate excellent optics for narrow-band THz applications.     

Fluctuation polarimetry

We examine the relationship between the strength of the intensity fluctuations and the polarimetric properties of a random electromagnetic field composed of a Gaussian, random field, and nonrandom field, and we present a method for determining the state of polarization of the Gaussian random field. The approach relies on incoherently mixing a Gaussian random field with a controllable reference field and measuring the intensity fluctuations of their superposition. We demonstrate that by controlling the reference field, the full polarimetric information about the Gaussian random field can be uniquely determined.     

Dynamic photoelastic analysis by optical heterodyne polarimetry

This paper describes the mapping of the spatiotemporal principal stress distribution evolved with time in an epoxy photoelastic sample. In the optical heterodyne polarimeter exploited, the signal beam of light transmitted by the sample under continuously loaded condition is photomixed with the local oscillator beam of light made up of orthogonal linearly polarized two-frequency components. Every pixel of a MOS video camera used generates a beat photocurrent that possesses the two orthogonal field components of the elliptically polarized signal beam. The spatiotemporal principal stress distributions can be uniquely determined simultaneously and independently from these two orthogonal field components, and are successfully mapped in a time-sequential form. The spatial and temporal resolutions in the maps are 0.18 mm and 2.9 ms, respectively.     

Stellar X-ray polarimetry

Summary Stellar X-ray polarimetry has for a long time been indicated as a very powerful diagnostic tool. In spite of this widely recognised interest, positive results are limited to just one: the detection, in the now far 1978, of the polarisation of the X-ray emission from the Crab Nebula. Novel-generation experiments promise a wider and richer amount mess of results, at least for strong galactic sources. Polarimetry however, remains an unusually delicate technique that requires a very tight control of systematic effects (at the level of 1% or better) over the very long observing period (10⁵ seconds or more) needed for obtaining a reasonable sensitivity. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Sub-shot-noise heterodyne polarimetry

We report an experimental demonstration of a heterodyne polarization rotation measurement with a noise floor 4.8 dB below the optical shot noise by use of classically phase-locked quantum twin beams emitted above threshold by an ultrastable type II Na:KTP cw optical parametric oscillator. We believe that this is the largest noise reduction achieved to date in optical phase-difference measurements.     

Stochastic scattering polarimetry

We introduce the general concept of stochastic scattering polarimetry and demonstrate that the anisotropic polarizability of a scattering object can be obtained by analyzing the statistical moments of polarimetrically measured intensity distributions. This general procedure is valid even in situations where the state of polarization of the incident field is not known. The efficiency of recovering different scattering polarizabilities is demonstrated numerically for several particular cases pertaining to both far- and near-field optics.     

基于太赫兹技术的药物检测

鉴于太赫兹辐射特有的光谱分辨性、功能性成像特点以及良好的穿透性和安全性等,太赫兹波谱技术迅速成为物质分析与检测等的重要工具。文章基于太赫兹时域光谱技术的实验数据,结合泛函密度理论(DFT)和HIPHOP模型,对一系列降糖类药物进行分子解析和功能基团识别;结合支持向量机理论(SVM),对4种郁金类中草药进行分析识别;并结合差式扫描量热法对葡萄糖—水合物的结晶水状态进行测定;最后对太赫兹时域技术在药物检测方面的优势和不足做了进一步的分析与展望。     

A4 Compton polarimetry

For the A4 parity violation experiment at MAMI we have installed a Compton laser polarimeter in our beam line. We have now operated this polarimeter at different beam energies of 315, 855, and 1508 MeV. A short overview of our detectors for scattered photons and electrons is given, together with a discussion of the extraction of Compton asymmetries using tagged photon spectra.     

Confocal scanning laser ophthalmoscopy improvement by use of Mueller-matrix polarimetry

A new technique for improving the signal-to-noise ratio and the contrast in images recorded with a confocal scanning laser system is presented. The method is based on the incorporation of a polarimeter into the setup. After the spatially resolved Mueller matrix of a sample was calculated, images for incident light with different states of polarization were reconstructed, and both the best and the worst images were computed. In both the microscope and the opthalmoscope modes, the best images are better than the originals. In contrast, the worst images are poorer. This technique may be useful in different fields such as confocal microscopy and retinal imaging.     

Detection of shear picosecond acoustic pulses by transient femtosecond polarimetry

Femtosecond transient polarimetry has been applied for the detection picosecond acoustic pulses generated in a thin film of zinc oxide (ZnO) deposited on an anisotropic zinc crystal surface. The measurements of the variations of the azimutal and the ellipticity angles describing the ultrafast variations of the state of polarisation (SOP) of the reflected light have been obtained. These polarimetric signals, interpreted as a SOP path on the Poincaré sphere, provide a sensitive method to detect acoustic echoes, particularly for shear acoustic pulses.     

Magnetic structures and neutron polarimetry

In a thermal neutron scattering experiment, Spherical Neutron Polarimetry (SNP) requires that the incident and the final neutron polarization vectors be measured independently. The method exploits the maximum information one can get from magnetic neutron scattering. Recently, it has been used quite successfully in the study of antiferromagnetic structures and their domain populations. The challenging measurement is now straightforward with our neutron polarimeter CRYOPAD as long as the sample chamber does not contain any magnetic field. Polarimetry on magnetized samples remains the domain of the classical Uniax ial Polarization Analysis (UPA) which measures only the longitudinal component of polarization in an applied field.     

Surface charge measurement in surface dielectric barrier discharge by laser polarimetry

Measurements of surface charge in a surface dielectric barrier discharge driven in atmospheric air were successfully demonstrated by a laser polarimetry. AC voltage at a frequency of 2 kHz generated the discharge between an exposed electrode and the dielectric barrier over a buried electrode. Although the discharge behaviors varied depending on the polarity of the exposed electrode, there were no differences in the tendency and amplitude of the surface charge accumulation except the polarity. With higher applied voltage, the amount of surface charge became larger and the charge was distributed farther from the exposed electrode.     

Modulation polarimetry of thermoelasticity induced by thermal radiation in a glass

The phenomenon of thermoelasticity induced by an external thermal radiation in a model glass sample was investigated experimentally. The thermoelasticity was detected by the optical polarization method used in studies of the photoelastic effect and modified by the probe radiation polarization modulation technique. This technique made it possible to increase the sensitivity of the measurement system to the strain state of a solid so that it became possible to detect thermoelasticity under conditions where the temperature gradient across the sample reaches a few fractions of a degree. The spatial and temporal changes of the mechanical stresses induced in the sample by a nonuniform radiation heating and, consequently, by a heat flux were measured. The coordinate functions of temperature as solutions of the inverse problem of thermoelasticity were obtained using the graphical integration of the experimental characteristics. The characteristic parameters of some of the heat transfer mechanisms were determined by analyzing the experimental characteristics of the kinetics and dynamics of mechanical stresses.     

Linear polarimetry of five comets

We made linear polarimetry of five comets, C/1989 X1 (Austin), 109P/Swift-Tuttle, C/1996 B2 (Hyakutake), C/1995 O1 (Hale-Bopp), and C/1996 Q1 (Tabur) simultaneously at eight wavelengths, in order to study phase angle and wavelength dependence of polarization in continuum light, and polarization behavior of molecular origin.

Polarization in continuum of Swift-Tuttle and Hyakutake were rather high i.e. similar to that of 1P/Halley, while those of Austin and Tabur were low in the positive branch. Hale-Bopp showed the highest polarization ever observed at the corresponding phase angles in the positive branch.

We also made observations scanning across the coma for Hyakutake and Hale-Bopp to investigate polarization structure. For Hale-Bopp, we found: (1) The position of maximum polarization was not at the visible center, and a red part was observed in the central region. (2) Optical properties and/or size spectrum of dust varied in a jet. On the contrary, any peculiar structure was not found for Hyakutake in spite of a much finer spatial resolution. The scanning observation of Hale-Bopp suggests that dust including its size spectrum evolves after the ejection from the nucleus, and that the optical depth in the central region plays an important role.     

Optical polarimetry of random fields

The state of polarization of an optical field provides detailed information concerning both the radiation emission processes and the intricate interaction between light and matter. We report here a novel approach for characterizing the polarization properties of electromagnetic fields for which the electric field vector at a point may fluctuate in three dimensions. Using probes which couple all three components of the field, we were able to extract the polarized and unpolarized components of such fields. Our results constitute the proof of concept for what could be called three-dimensional optical polarimetry.     

Study on low-energy positron polarimetry

A polarised positron source has been proposed for the design of the international linear collider (ILC). In order to optimise the positron beam, a measurement of its degree of polarisation close to the positron creation point is desired. In this contribution, methods for determining the positron polarisation at low energies are reviewed. A newly developed polarisation extension to GEANT4 will provide the basis for further polarimeter investigations.