Octave-spanning single-cycle middle-infrared generation through optical parametric amplification in LiGaS2.

Bo-Han Chen,Peter Baum,Emanuel Wittmann,Eberhard Riedle,Yuya Morimoto

doi:10.1364/oe.27.021306

Abstract

We report the generation of extremely broadband and inherently phase-locked mid-infrared pulses covering the 5 to 11 µm region. The concept is based on two stages of optical parametric amplification starting from a 270-fs Yb:KGW laser source. A continuum seeded, second harmonic pumped pre-amplifier in β-BaB2O4 (BBO) produces tailored broadband near-infrared pulses that are subsequently mixed with the fundamental pump pulses in LiGaS2 (LGS) for mid-infrared generation and amplification. The pulse bandwidth and chirp is managed entirely by selected optical filters and bulk material. We find an overall quantum efficiency of 1% and a mid-infrared spectrum smoothly covering 5-11 µm with a pulse energy of 220 nJ at 50 kHz repetition rate. Electro-optic sampling with 12-fs long white-light pulses directly from self-compression in a YAG crystal reveals near-single-cycle mid-infrared pulses (32 fs) with passively stable carrier-envelope phase. Such pulses will be ideal for producing attosecond electron pulses or for advancing molecular fingerprint spectroscopy.

Highlights

Few-cycle, high-field and phase-stable laser pulses in the mid-infrared (MIR) range of the optical spectrum are essential for many applications [1,2,3], especially for strong-field physics in solids [4], all-optical electron pulse compression [5] or molecular fingerprint spectroscopy [6,7,8,9]
The concept is based on two stages of optical parametric amplification starting from a 270-fs Yb:KGW laser source
The second part with 138 μJ goes into a noncollinear optical parametric amplifier system (NOPA, dotted outline) in which ∼2 μJ are used for white-light generation [32]; 136 μJ are used for second-harmonic generation with 30% efficiency. 40 μJ at 513 nm are used to pump the noncollinear OPA (NOPA) crystal

Summary

Introduction

Few-cycle, high-field and phase-stable laser pulses in the mid-infrared (MIR) range of the optical spectrum are essential for many applications [1,2,3], especially for strong-field physics in solids [4], all-optical electron pulse compression [5] or molecular fingerprint spectroscopy [6,7,8,9]. As compared to the currently popular spectral broadening of the full pump laser output in various media, we use just a small amount of light to obtain the necessary broadening and frequency shift in a bulk YAG crystal and subsequently add power by a first OPA stage. This concept allows to control and adjust the pulses’ spectral and dispersive properties without the need for specially tailored chirped mirrors or luck with the properties of the nonlinear process. With only one more nonlinear conversion step as compared to spectral broadening and OR, the overall energy conversion efficiency is quite competitive

Experimental setup

Dispersion estimation

Findings

Beam quality