Integration of a rapid scanning technique into THz time-domain spectrometers for nonlinear THz spectroscopy measurements.

C. Hoberg,M. Havenith,P. Balzerowski

doi:10.1063/1.5080653

Abstract

We have implemented a rapid scanning technique into THz time-domain spectrometers using an oscillating frictionless delay line, especially adapted for nonlinear THz experiments. Thereby we were able to increase the dynamic range of THz measurements in the frequency range from 40 to 200 cm-1 by up to 24 dB and reduce the scanning time by up to a factor of 200. We report here test measurements on TDS-setups at repetition rates of 80 MHz and 5 kHz. The dynamic range exceeds 64 dB, which allows to record even small changes in the THz absorption upon optical excitation by a THz probe, covering the frequency range of the intermolecular modes and the phonon bands. We demonstrate the potential of this technique for optical-pump THz-probe experiments using a 70 μm thick high-resistivity silicon, excited by 400 nm, ∼50 fs pulses as a sample.

Highlights

THz time-domain spectroscopy (TDS) has developed into a powerful spectroscopic method for linear and nonlinear THz spectroscopy in the frequency range from 0.3 to 10 THz
The delay time between the THz pulse and the probe pulse is controlled by varying the path length between the THz and detection pulse, conventionally using mechanical delay lines
A high frequency digital lock-in amplifier or boxcar integrator is used for low-frequency noise reduction. We demonstrate that this rapid scanning technique can be applied in THz time-domain systems with low as well as high laser repetition rates while improving the dynamic range by up to 24 dB. We demonstrate that this rapid scanning technique can be applied to nonlinear THz techniques that utilize more than one delay line, such as optical-pump THz-probe experiments (OPTP) to reduce scanning times by a factor of 20 or more

Summary

INTRODUCTION

THz time-domain spectroscopy (TDS) has developed into a powerful spectroscopic method for linear and nonlinear THz spectroscopy in the frequency range from 0.3 to 10 THz. Conventional TDS setups are based on ultrafast laser sources. This requires the use of amplified laser systems which generate ultrashort, high-energy pulses (1-10 mJ and more) These laser systems are operated at low repetition rates of 1-10 kHz. Whereas previously reported rapid scanning techniques focused on high repetition laser systems we focus here on an alternative technique which is compatible with both, high and low repetition rate laser systems. We demonstrate that this rapid scanning technique can be applied in THz time-domain systems with low as well as high laser repetition rates while improving the dynamic range by up to 24 dB. We demonstrate that this rapid scanning technique can be applied to nonlinear THz techniques that utilize more than one delay line, such as optical-pump THz-probe experiments (OPTP) to reduce scanning times by a factor of 20 or more

Integration of rapid scanning techniques in MHz repetition rate systems

Integration of rapid scanning in KHz repetition rate systems

INTEGRATION OF RAPID SCANNING TECHNIQUES FOR NONLINEAR THz SPECTROSCOPY

SUMMARY