Phase-Coherent Frequency Combs in the Vacuum Ultraviolet via High-Harmonic Generation inside a Femtosecond Enhancement Cavity

TLDR

The study demonstrates generation of phase‑coherent frequency combs in the vacuum ultraviolet. The output of a mode‑locked laser is stabilized to a femtosecond enhancement cavity with a gas jet at the intracavity focus, and the resulting high‑peak power enables efficient high‑harmonic generation at the laser’s full repetition rate. Optical‑heterodyne measurements show that the comb structure of the original laser is preserved in the high‑harmonic generation, enabling precision frequency metrology at extreme ultraviolet wavelengths and efficient generation of phase‑coherent high‑order harmonics with a standard laser oscillator.

Abstract

We demonstrate the generation of phase-coherent frequency combs in the vacuum utraviolet spectral region. The output from a mode-locked laser is stabilized to a femtosecond enhancement cavity with a gas jet at the intracavity focus. The resulting high-peak power of the intracavity pulse enables efficient high-harmonic generation by utilizing the full repetition rate of the laser. Optical-heterodyne-based measurements reveal that the coherent frequency comb structure of the original laser is fully preserved in the high-harmonic generation process. These results open the door for precision frequency metrology at extreme ultraviolet wavelengths and permit the efficient generation of phase-coherent high-order harmonics using only a standard laser oscillator without active amplification of single pulses.