High-power femtosecond mid-IR source with tunable center frequency and chirp

TL;DR

This paper reports an experimental high-power, tunable femtosecond mid-IR laser source capable of variable frequency and large spectral sweep, useful for driving vibrational modes without dielectric breakdown.

Contribution

It introduces a novel chirped difference-frequency generation method for generating high-power, tunable mid-IR pulses with large spectral sweep and high electric fields.

Findings

Achieved mid-IR electric fields of 1.5 MV/cm at 4 THz.

Demonstrated continuous frequency tuning of up to 20% within a pulse.

Validated experimental results with numerical simulations.

Abstract

We present an experimental implementation of a chirped mid-infrared (mid-IR) high-power laser source with variable center frequency between 4 THz to 30 THz and continuously tunable frequency sweep of up to 20 % within one pulse, with a pulse duration of 2 ps. The peak electric field obtained at 4 THz is 1.5 MV/cm. We generate the mid-IR light using a difference-frequency generation (DFG) process with two phase-locked, chirped IR pulses. The obtained mid-IR electric field waveform is characterized using electro-optic sampling. We compare our experimental results with the predictions of numerical simulations. The results indicate the potential for efficient driving of vibrational modes into a strongly anharmomic regime, in cases where using Fourier-transform-limited pulses to achieve similar vibrational amplitudes would lead to dielectric breakdown.