An ultra-stable, widely tunable and Cs-traceable mid-IR coherent source

We will report on recent results of experiments carried out to reference and spectrally characterize mid-IR coherent radiation to an optical frequency comb (OFC) based on a Ti:sapphire fs laser covering the visible/near-IR spectrum. The diode laser (pump), which is tunable in the 838 divide 863 nm, and the Nd:YAG laser (signal) at 1064 nm are mixed to generate the mid-IR radiation (idler), being phase-locked to two nearby OFC teeth which are about 70 THz apart each other. The idler frequency is tunable on demand at any wavelength in the 3950 divide 4570 nm and the achievable power varies in the 300 divide 80 muW range. The OFC parameters (repetition rate, tooth order) directly yields the absolute frequency of the DFG radiation, while the phase-lock loops narrow the IR linewidth well below the free-running value. Indeed the intrinsic linewidth was measured to be as low as 10 Hz.