Intensity noise in mid-IR frequency combs based on difference frequency generation

Coherent frequency conversion processes for frequency combs (FCs) are intensively studied as they inter alia enable the use of FCs for precision spectroscopy in the important mid-infrared (MIR) spectral region not covered by laser gain media. Difference frequency generation (DFG) is one promising approach for a simple and robust scheme to generate phase-stable MIR FCs. When used in a spectroscopy experiment, relative intensity noise (RIN) constitutes a major obstacle to achieve high signal-to-noise ratios (SNR) and long averaging times but only a very limited numbers of studies address this issue [1-3]. In this contribution, we report on RIN studies of a DFG MIR source. We found a strong dependence of the MIR idler noise on the delay between pump and signal field. A dither-lock technique was implemented to enable long-term stable and low-noise operation.