Femtosecond pulse shaping directly in the mid-IR using acousto-optic modulation

TLDR

The study demonstrates pulse shaping directly in the mid‑IR by employing a germanium acousto‑optic modulator capable of programmable phase and amplitude modulation across 2–18 µm. The authors use the germanium acousto‑optic modulator to programmatically control the phase and amplitude of mid‑IR pulses. The Ge AOM produces 4.9 µm shaped pulses with 50 % throughput, high resolution, and stable phase, enabling their use in phase‑sensitive experiments such as heterodyned 2D IR spectroscopy.

Abstract

Pulse shaping directly in the mid-IR is accomplished by using a germanium acousto-optic modulator (Ge AOM) capable of programmable phase and amplitude modulation for IR light between 2 and 18 μm. Shaped waveforms centered at 4.9 μm are demonstrated in both the frequency and the time domains. With a 50% throughput efficiency, the Ge AOM can generate much more intense pulses with higher resolution than can indirect shaping methods. Furthermore, the phase stability of the shaped pulse proved sufficient for cross correlation with unshaped mid-IR pulses. Thus, phase- and amplitude-tailored pulses can now be readily incorporated into phase-sensitive experiments, such as heterodyned 2D IR spectroscopy.