Energetic mid-IR femtosecond pulse generation by self-defocusing soliton-induced dispersive waves in a bulk quadratic nonlinear crystal

TL;DR

This paper demonstrates a simple, efficient method to generate energetic mid-IR femtosecond pulses using a bulk quadratic nonlinear crystal, avoiding complex parametric processes and phase-matching requirements, with potential for scalable ultrafast spectroscopy applications.

Contribution

The authors introduce a novel, straightforward technique for mid-IR femtosecond pulse generation using self-defocusing solitons in bulk quadratic crystals, eliminating the need for synchronization and critical phase-matching.

Findings

Generated up to 10.5 μJ mid-IR pulses at 3 μm with high quality

Achieved broadband tunability (~1000 cm⁻¹) in mid-IR pulses

Method is scalable and adaptable to other crystals and wavelengths

Abstract

Generating energetic femtosecond mid-IR pulses is crucial for ultrafast spectroscopy, and currently relies on parametric processes that, while efficient, are also complex. Here we experimentally show a simple alternative that uses a single pump wavelength without any pump synchronization and without critical phase-matching requirements. Pumping a bulk quadratic nonlinear crystal (unpoled LiNbO$_3$ cut for noncritical phase-mismatched interaction) with sub-mJ near-IR 50-fs pulses, tunable and broadband ($\sim 1,000$ cm$^{-1}$) mid-IR pulses around $3.0~\mu\rm m$ are generated with excellent spatio-temporal pulse quality, having up to 10.5 $\mu$J energy (6.3% conversion). The mid-IR pulses are dispersive waves phase-matched to near-IR self-defocusing solitons created by the induced self-defocusing cascaded nonlinearity. This process is filament-free and the input pulse energy can therefore be scaled arbitrarily by using large-aperture crystals. The technique can readily be implemented with other crystals and laser wavelengths, and can therefore potentially replace current ultrafast frequency-conversion processes to the mid-IR.