Description
We demonstrate a compact and reliable dual-stage bulk post-compression system designed to deliver high-energy, single-cycle mid-IR pulses at high repetition rates for strong-field physics and attosecond spectroscopy. Operating at a 100 kHz repetition rate, the system compresses 42 fs pulses centered at 3.2 µm from an 8.5 W optical parametric chirped-pulse amplifier (OPCPA). Nonlinear spectral broadening is achieved via self-phase modulation through an optimized tandem configuration of BaF₂ and Si plates arranged in a confocal setup of spherical mirrors, preventing optical damage while maximizing bandwidth. The first stage shortens the pulses to 15 fs (1.5 optical cycles) with 55 µJ of energy. The second stage further extends the spectral coverage from 1.8 to 4.2 µm, delivering nearly transform-limited 11.2 fs pulses (1.1 optical cycles) at a central wavelength of 3.1 µm, with an output energy of 30 µJ. Dispersion compensation is managed using a combination of fluoride windows CaF₂/BaF₂ and custom third-order dispersion (TOD) mirrors.
Temporal and spatio-temporal diagnostics via TIPTOE and ICE techniques confirm high spatial homogeneity, a clean temporal profile, and negligible pulse front tilt. The system exhibits excellent long-term performance over extended operations, maintaining an average power stability of 0.62% RMS, beam pointing control within 28 µm RMS, and an integrated yield spectrum stability of 3.23%. Furthermore, active closed-loop feedback provides an exceptional CEP stability of 145 mrad RMS. The practical utility of this high-flux source is validated by driving stable, multi-octave high-harmonic generation (H3–H13) within a bulk ZnO crystal, confirming its suitability as a robust driver for future user-facility experiments and attosecond science.
