THz generation by optical rectification of near-infrared laser pulses in the organic nonlinear optical crystal HMQ-TMS

Fabian D J Brunner,Seung-Heon Lee,O-Pil Kwon,Thomas Feurer

doi:10.1364/ome.4.001586

Abstract

We show that the organic electro-optic crystal HMQ-TMS [2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate] has favorable properties for the parametric generation of THz waves in a collinear type-0 phase-matching scheme, i.e., a low absorption coefficient at wavelengths from 800 to 1500 nm (α 0.5 mm). We demonstrate efficient generation of broadband THz pulses through optical rectification of sub-picosecond laser pulses in a 0.2 mm thick HMQ-TMS crystal at the wavelength of 1000 nm. The energy conversion efficiency achieved in this crystal was 41 times higher than the one achieved in a 0.3 mm thick GaP crystal, which is an often used material for collinearly phase-matched THz generation at this laser wavelength. The peak amplitudes of the THz signal obtained with the HMQ-TMS crystal were 5.4 times larger in the time-domain and 7.1 times larger in the frequency-domain than the ones obtained with the GaP crystal.

Highlights

Optical rectification of femtosecond laser pulses in an electro-optic crystal is an often used method for the generation of broadband THz pulses [1]
A high conversion efficiency in this process is crucial for both THz imaging and spectroscopy applications, because it leads to a high signal-to-noise ratio and can enable nonlinear optics experiments relying on intense THz pulses
Broadband THz pulses can be generated at room temperature in the organic crystals DAST (4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate), DSTMS (4-N,Ndimethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate), and OH1 {2-[3(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene]malononitrile} with conversion efficiencies up to 2 % at laser wavelengths between 1.3 μm and 1.5 μm [8,9,10,11,12]

Summary

Introduction

Optical rectification of femtosecond laser pulses in an electro-optic crystal is an often used method for the generation of broadband THz pulses [1]. A high conversion efficiency in this process is crucial for both THz imaging and spectroscopy applications, because it leads to a high signal-to-noise ratio and can enable nonlinear optics experiments relying on intense THz pulses It requires a crystal with a high transparency in the near-infrared (NIR) and THz spectral range and a high nonlinear optical susceptibility tensor element which can be exploited in a phase-matching scheme. A conversion efficiency of 3.8 % was demonstrated in the inorganic ferroelectric crystal LiNbO3 at a laser wavelength of 1 μm, a more sophisticated Cherenkov phase-matching scheme and cryogenic cooling was required and the bandwidth of the generated THz pulses was relatively small [7]. We report on the linear optical properties of the HMQ-TMS crystal for light polarized along its polar axis in the visible and infrared spectral range from 600 to 2000 nm and in the THz spectral range from 0.3 to 1.5 THz, discuss the phase-matching characteristics at various laser wavelengths based on this information and demonstrate efficient THz generation pumped at 1000 nm

Basic properties

Optical properties

Generation of THz pulses in HMQ-TMS crystals

Findings

Conclusions