Mid-infrared frequency comb based-on low threshold optical parametric oscillator

Summary form only given. Over the last decade, Frequency combs (FCs) have triggered new attractive methods for absorption spectroscopy and have been successfully implemented in the visible and near-infrared spectral region. When combined with Fourier transform spectrometers, it shows remarkable advantages of large spectral bandwidth, high spectral resolution and high sensitivity. For trace gas detection, extending the wavelength of FCs in the mid-infrared region is beneficial, as many molecules exhibit here their strongest absorption lines. Several methods have been proposed to extend FCs in the mid-infrared region [1]. Among those methods, Optical Parametric Oscillators (OPOs) are used as efficient light converters [2].Here we report on a FC-based single resonant OPO for the 3.5 μm region with low threshold power. The designed OPO consists of a 1 mm-long periodically polled MgO-doped PPLN crystal pumped by an Yb-fiber laser. A schematic of the setup is depicted in Fig. 1a. The pump laser is a femtosecond laser delivering up to 2 W, 80 fs optical pulses at 1.04 μm. The repetition rate of the laser is stabilized by a frequency generator at 90 MHz. The OPO cavity is designed with a 6-mirrors linear cavity. To compensate the light dispersion of the cavity introduced by the crystal and the curved mirrors, the 1.7 m long linear cavity is folded with chirped mirrors. One of the chirped mirrors is mounted on a piezo actuator to stabilize the cavity length.