Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region.

We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6-18 µm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse difference-frequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 µm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-µm pulses in GaSe.

High-power frequency comb at 2 µm wavelength emitted by a Tm-doped fiber laser system.

We report on the generation of a high-power frequency comb in the 2 µm wavelength regime featuring high amplitude and phase stability with unprecedented laser parameters, combining 60 W of average power with <30 fs pulse duration. The key components of the system are a mode-locked Er:fiber laser, a coherence-preserving nonlinear broadening stage, and a high-power Tm-doped fiber chirped-pulse amplifier with subsequent nonlinear self-compression of the pulses. Phase locking of the system resulted in a phase noise of less than 320 mrad measured within the 10 Hz-30 MHz band and 30 mrad in the band from 10 Hz to 1 MHz.