Generation and spectral manipulation of coherent terahertz radiation with two-stage optical rectification

Ching-Wei Chen,Li Yan,Yu-Shian Lin,Jung Y. Huang,Chen-Shiung Chang,Chao-Kuei Lee,Ci-Ling Pan

doi:10.1364/oe.16.014294

Abstract

We propose and experimentally demonstrate the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the terahertz field injected from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of coherent THz radiation. The technique is also potentially useful for generating high-power single-cycle terahertz pulses, usually limited by the pulse walk-off effect of the nonlinear optical crystal used.

Highlights

Tremendous efforts have recently been focused on developing intense terahertz (THz) radiation sources for spectroscopy, security inspections, and biomedical imaging
The curve of open squares was acquired with the same setup by blocking the pump pulse to the second GaSe crystal and scanning the delay time of the probe beam for the THz
By properly adjusting the time delay between the pump pulses to the two Optical rectification (OR) stages, the terahertz radiation field generated by the second stage can be constructively superposed to the injecting terahertz field from the first stage

Summary

Introduction

Tremendous efforts have recently been focused on developing intense terahertz (THz) radiation sources for spectroscopy, security inspections, and biomedical imaging. Cascaded OR processes in nonlinear optical crystals for intense terahertz pulse generation was reported [15]. The authors considered both the perfect phase matching without loss and the realistic phase matching with linear absorption in ZnTe crystals. By using two temporally and spatially separated ultrafast optical excitation pulses, the researchers can control the propagating lattice excitations of a ferroelectric crystal and in principle tailor the terahertz-frequency fields that are radiated by the phonon-polariton wave packets. We reported in this study the successful generation of single-cycle high-amplitude terahertz radiation pulses with cascaded GaSe optical rectification stages

Theoretical model and experimental methods

Results and discussions

Conclusions