Abstract

We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications.

Highlights

  • Optical polarization sensing and spectroscopy are fundamental experimental tools in materials science

  • Terahertz time-domain polarimetry, which allows us to extract the instantaneous direction of the electric-field (E-field) vectors within a single-cycle of the electromagnetic oscillation, opens new avenues for investigating the surface topography of materials [37] and for separate determination of the optical Faraday and Kerr rotation angles using echo signals [26], a result that cannot be attained with the conventional polarization measurement technique for much higher frequencies

  • We recently proposed and demonstrated a new experimental scheme for the terahertz polarization measurement involving rapidly rotating the EO crystal [72] to modulate the EO signal; this is much easier to achieve than it would be with the wire-grid counterpart since the EO crystal is much smaller than the wire-grid polarizers and it is quite easy to achieve a stable rotation with a frequency up to 100 Hz (6,000 rotations per minute)

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Summary

Introduction

Optical polarization sensing and spectroscopy are fundamental experimental tools in materials science. Polarization spectroscopy and ellipsometry in the terahertz frequency range with a much lower photon energy of several meV have become a challenging research area in last two decades [7,8,9,10] These techniques have become important tools for investigating low-energy dynamical phenomena in various kinds of materials such as molecules [11,12], superconductors [13,14,15,16,17], multiferroics [18], two-dimensional electron gases [19], graphene [20], magnetic materials [21,22,23,24,25] and topological insulators [26,27]. Terahertz time-domain polarimetry, which allows us to extract the instantaneous direction of the electric-field (E-field) vectors within a single-cycle of the electromagnetic oscillation, opens new avenues for investigating the surface topography of materials [37] and for separate determination of the optical Faraday and Kerr rotation angles using echo signals [26], a result that cannot be attained with the conventional polarization measurement technique for much higher frequencies

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