Divide-and-conquer approach to the generation of mid-infrared frequency combs

Abstract

Extending the range of precision phase-stabilized optical frequency combs to the highly desirable yet challenging mid-IR region is of great interest for numerous applications including molecular spectroscopy, trace detection, and laser-driven particle acceleration. Several methods were developed lately for extending frequency combs to the mid-IR, including supercontinuum generation in optical fibers [1] and engineered χ(2) nonlinear-optical devices [2], optical rectification [3], difference-frequency generation [4,5], optical parametric oscillators (OPOs) [6,7] and amplifiers [8], and direct laser sources [9]. Our novel approach for producing mid-IR frequency combs is based on frequency division, namely transposing the frequency comb of the pump laser to the half of its central frequency in a degenerate optical parametric oscillator (OPO). This approach offers the following major advantages: simplicity of the setup, low (∼100 mW) pump power required, potential for high (> 90%) conversion efficiency where most of the pump photons are converted into subharmonic, and possibility to dramatically exceed the bandwidth of the pump frequency comb, thanks to cross mixing combined with an enormous acceptance bandwidth, typical for type 0 or type I OPOs at degeneracy [10].