Cascaded half-harmonic generation of femtosecond frequency combs in the mid-infrared

Abstract

There is a growing demand for frequency combs in the mid-infrared (mid-IR), also known as the “molecular fingerprint” region of the spectrum. Down-conversion of near-IR frequency combs by half-harmonic generation is a simple way to extend the wavelength coverage of stable frequency combs to this region, and has benefits such as high conversion efficiency and intrinsic phase and frequency locking to the near-IR pump. Here, we report a two-octave down-conversion of a frequency comb around 1 μm through cascaded half-harmonic generation with ∼64% efficiency in the first stage and ∼18% in the second stage. The high conversion efficiency and stable broadband operation indicate the effectiveness and potential of cascaded half-harmonic generation for the realization of intrinsically locked long-wavelength sources, which can be beneficial for numerous applications.