Mid-IR femtosecond frequency conversion by soliton-probe collision in phase-mismatched quadratic nonlinear crystals

TL;DR

This paper demonstrates numerically that ultrashort self-defocusing solitons in quadratic nonlinear crystals can efficiently convert near-IR pulses into mid-IR wavelengths through soliton-probe collisions, utilizing cascaded nonlinear effects.

Contribution

It introduces a novel mid-IR frequency conversion method using soliton-probe collisions in quadratic nonlinear crystals, highlighting high efficiency and specific dispersion regimes.

Findings

Near-perfect conversion efficiency achievable.

Mid-IR wave formed as a resonant dispersive wave.

Effective negative cross-phase modulation mediates four-wave mixing.

Abstract

We show numerically that ultrashort self-defocusing temporal solitons colliding with a weak pulsed probe in the near-IR can convert the probe to the mid-IR. A near-perfect conversion efficiency is possible for a high effective soliton order. The near-IR self-defocusing soliton can form in a quadratic nonlinear crystal (beta-barium borate) in the normal dispersion regime due to cascaded (phase-mismatched) second-harmonic generation, and the mid-IR converted wave is formed in the anomalous dispersion regime between $\lambda=2.2-2.4~\mu\rm m$ as a resonant dispersive wave. This process relies on non-degenerate four-wave mixing mediated by an effective negative cross-phase modulation term caused by cascaded soliton-probe sum-frequency generation.