Polarization shaping of near-infrared femto second pulse for transport measurement of semiconductor

Hironori Ito^1*, Tetsuo Nakano², Shintaro Nomura², Kazuhiko Misawa¹

¹Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo, Japan
²Division of Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan

* Presenter:Hironori Ito, email:h-ito@cc.tuat.ac.jp

Polarization shaping of near-infrared femto second pulse consisting of 4f set-up and a spatial light modulators can control phases of each frequency components individually. It is possible to arbitrarily control the direction and frequency of the helicity of the optical pulse in terahertz regime.[1] This pulse, called a polarization-twisted pulse that can cause Raman-active excitation.[2] It is distinguish from a circularly polarized terahertz pulse that can cause infrared-active excitation. This method enables us to investigate response of semiconductor samples at 0~50 THz. In this presentation, we demonstrate that the direction of the photocurrent generated in the modulation doped GaAs/AlGaAs quantum well switches according to the direction of the polarization envelope helicity of the near-infrared pulses.
Optical pulses from a mode-locked fs Ti: sapphire laser were introduced to a 4f set-up for the arbitrary vector field shaping. The spectral range of optical pulses are from 700 nm to 900 nm. Phases of diagonally polarized components of each frequency are controlled independently by dual pixel masks of spatial light modulators. In this experiment, group delay dispersion is 16000 fs^2, and pulse durations are 3.0 ps.Superposition of these components has envelope helicity with arbitrary terahertz frequency.
The shaped pulses were incident on the surface of a 400 × 1600 μm^2 hall-bar structure of n-type GaAs/AlGaAs (001) modulation doped quantum well in a He cryostat at 5 K. The incident angle is 20 degrees from the direction perpendicular to the substrate.The helicity of twisted polarization pulse modulated at 50 kHz by a photoelastic modulator (PEM), and the helicity dependent photovoltages were detected synchronously with a lock-in amplifier.
As a result, differential voltages between the clockwise helicity and the counterclockwise helicity illumination were monotonically increased up to around 50 THz. This observation unambiguously demonstrates that the direction of the current flowing in the quantum well is reversed, depending on the envelope helicity of the pulse. In order to ensure this result, the envelope helicity was reversed by tuning of only SLM condition. In this case, the sign of the current was reversed. In this oblique incident condithin, longitudinal photovoltages were about 10 times the transverse voltage. This is well explaind by circular photogalvanic effect[3] including the spin-spited conduction intersubband transition. These experimental results were obtained for the first time by introducing the concept of waveform shaping of optical pulses to the semiconductor transport measurement.
Reference:
[1] M. Sato et. al., Nature Photon. 7, 724 (2013).
[2] T. Higuchi et. al., Phys. Rev. A 87, 013808 (2013).
[3] S. D. Ganichev et. al., Phys. Rev. B 68, 035319 (2003).

Keywords: Quantum well, GaAs/AlGaAs, Pulse shaping, Femto second pulse, Transport measurement