Seeded optical parametric oscillator light source for precision spectroscopy

Abstract

Precision spectroscopy of fundamental bands of molecules in the mid-infrared (MIR) region is of great interest in applications of trace detection and testing fundamental physics, where high-power and narrow-linewidth MIR lasers are needed. By using a frequency-stabilized near-infrared laser as a seed of the signal light of a continuous-wave optical parametric oscillator, we established a broadly tunable MIR light source that has an output power of several hundred milliwatts and a linewidth of a few tens of kilohertz. The MIR laser frequency drift was reduced to below 1 kHz by using an optical frequency comb to stabilize the frequency of the 1064 nm pumping laser. The performance of the light source was investigated and tested by measuring the saturated absorption spectroscopy of a few molecular transitions at 3.3 µm.

Mid-infrared Doppler-free saturation absorption spectroscopy of the Q branch of CH4ν3 = 1 band using a rapid-scanning continuous-wave optical parametric oscillator

“…Indeed, a linewidth of less than 2 MHz for the CH4 Doppler-free spectrum was achieved in our lab using a CTL (Toptica, CTL 1050). To further reduce the output linewidth, one can lock the OPO cavity to a seed laser, [37] a molecular transition, [18] or an external frequency reference, e.g., an ultra-low expansion cavity and frequency combs. [38] In the present work, most transitions are significantly power-broadened.…”