Broadband mid-IR frequency comb with CdSiP2 and AgGaS2 from an Er, Tm:Ho fiber laser

We report on the generation of a 2500 nm bandwidth frequency comb at 6.5 mu m central wavelength based on critically phase-matched parametric down-conversion in the nonlinear crystal CdSiP2 (CSP), driven by a compact Er, Tm: Ho fiber laser. The generated ultra-broadband pulses show a transform-limited duration of 2.3 optical cycles and carry up to 150 pJ of energy at a 100 MHz pulse repetition rate. For comparison, the spectrum generated in AgGaS2 (AGS) spans from 6.2 to 7.4 mu m at full-width at half-maximum (FWHM) with a pulse energy of 3 pJ. A full 3D nonlinear wave propagation code is used for optimization of the noncollinear angle, propagation direction, and crystal thickness. (C) 2014 Optical Society of America