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)
Summary
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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