Broadband, few-cycle mid-infrared continuum based on the intra-pulse difference frequency generation with BGSe crystals.

Jinwei Zhang,Ka Fai Mak,Heyan Liu,Zhuang Li,Jingjie Hao,Jie Liu,Jiyong Yao,Qing Wang

doi:10.1364/oe.411664

Abstract

We demonstrate for the first time the generation of octave-spanning mid-infrared using a BGSe nonlinear crystal. A Cr:ZnS laser system delivering 28-fs pulses at a central wavelength of 2.4 µm is used as the pump source, which drives the intra-pulse difference frequency generation inside the BGSe crystal. As a result, a coherent broadband mid-infrared continuum spanning from 6 to 18 µm has been obtained. It shows that the BGSe crystal is a promising material for broadband, few-cycle mid-infrared generation via frequency down conversion with femtosecond pump sources.

Highlights

Mid-infrared (MIR) light in the range of 2-20 μm is useful for chemical and biological identification due to the presence of many molecular characteristic absorption lines in this spectral region [1]
We demonstrate the generation of a coherent MIR output with a BGSe crystal via intra-pulse difference frequency generation (IDFG)
We have demonstrated a MIR source with the BGSe crystal based on the IDFG method

Summary

Introduction

Mid-infrared (MIR) light in the range of 2-20 μm is useful for chemical and biological identification due to the presence of many molecular characteristic absorption lines in this spectral region [1]. A coherent, few-cycle source with a simultaneous coverage of the broad MIR range can further enable new applications such as mirco-spectroscopy [2,3], femtosecond pump-probe spectroscopy [4], and high-dynamic-range sensitive measurements [5,6,7] Until now numerous schemes have been developed to generate coherent MIR radiation, such as synchrotron beam lines, quantum cascade lasers, supercontinuum sources [2], optical parametric oscillators (OPO) [8] and optical parametric amplifiers (OPA) These schemes all have their own strengths and weaknesses in terms of complexity, bandwidth, power, efficiency, and pulse durations. In contrast to GaSe, BGSe can be cut at the desired phase-matching angle and can be anti-reflection coated Another new chalcogenide nonlinear crystal BGGSe was developed and used for MIR generation [21,22], showing very similar transparency window and higher nonlinear coefficient (d11=66 pm/V) compared to BGSe. BGSe crystal can be more grown to a large dimensions to accommodate larger beam sizes [19]. The damage threshold of the BGSe crystal was characterized under femtosecond pulses with a central wavelength of 2.4 μm

Experimental setup

Conclusion