Picosecond Polarisation Detector for Infrared and Terahertz Radiation
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1016-CC01-04
Picosecond Polarisation Detector for Infrared and Terahertz Radiation Wolfgang Weber1, Josef Kiermaier1, Sergey N. Danilov1, Dieter Schuh1, Christian Gerl1, Werner Wegscheider1, Dominique Bougeard2, Gerhard Abstreiter2, Wilhelm Prettl1, and Sergey D. Ganichev1 1 Institute of Experimental and Applied Physics, University of Regensburg, Universit‰tsstrafle 31, 9305, Regensburg, Germany 2 Walter Schottky Institute, TU Munich, Garching, Germany, Muenchen, Germany, Muenchen, Germany ABSTRACT We report on a room temperature detector of laser light ellipticity allowing determination of azimuth, ellipse shape, and the sense of rotation of the light vector with subnanosecond time resolution. The detector operation is demonstrated for THz radiation detection, but the same technique can be extended for detection of infrared or visible light. The detection system is based on the simultaneous measurement of three different photocurrents obtained from three unbiased semiconductor detector elements stacked in-line together. INTRODUCTION The method of laser ellipsometry of transmitted, reflected, or scattered light has been emerged as a powerful technique for analysis of the optical anisotropy of various media such as plasmas, gases, solids and solid surfaces as well as biological tissues. Illustrative examples are: tokamak polarimetry to measure electric and magnetic fields in ionized gases and the plasma density, monitoring and control of material preparation and processing, circular dichroism spectroscopy and optical rotary dispersion of proteins and molecules, contactless and nondestructive measurements of surfaces and very thin films, analysis of gas and aerosol constituents in the EarthÃs atmosphere by polarization sensitive optical remote sensing. In all cases, information is gained about how the object transforms the incident polarization vector. An elliptically polarized light beam is defined by the angular position of the ellipse (azimuth), its shape (ellipticity), and the sense of rotation of the light vector. Traditionally optical anisotropy is studied making use of polarization sensitive optical elements which allow to determine the relative retardation or optical path difference between the orthogonal wavefronts (termed ordinary and extraordinary) that are introduced into the optical system by the object birefringence. Some tasks need measurement of dynamic ellipticity of polarized light. This is so far realized by transmitting passing of elliptical light through a rapidly rotating analyzing prism, ahead of a photodetector or by using of a pump-probe method. Here we report on a detector system which allows time resolved measurement of ellipticity and axis orientation of polarized light without any polarization dependent optical components. The detection system is based on the simultaneous measurement of three different photocurrent obtained from three unbiased semiconductor detector elements in response to laser radiation. The access to radiation helicity describing the rotation of light polarization vect
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