Continuous-wave optical parametric oscillators for mid-infrared spectroscopy

Abstract

The atmospheric window at 3 to 5 µm is one of the most important spectral regions for molecular spectroscopy. This region accommodates strong fundamental vibrational spectra of several interesting molecules, including species relevant for air quality monitoring, medical diagnostics, and fundamental research. These applications require excellent spectroscopic sensitivity and selectivity. For example, atmospheric research often needs precise quantification of trace gas fractions of down to the parts-per-trillion level (10 -12 ), with the capability of resolving individual spectral features of different molecular compounds. This sets stringent requirements for the light source of the spectrometer in terms of output power, noise, and linewidth. In addition, the wavelength tuning range of the light source needs to be large, preferably over the entire atmospheric window, in order to enable measurements of molecular fingerprints of several compounds. Continuous-wave optical parametric oscillators (CW-OPOs) are one of the few light sources that have the potential of combining all these favorable characteristics. This contribution summarizes our progress in the development of CW-OPOs, with an emphasis on precise frequency control methods for high-resolution molecular spectroscopy. Examples of new applications enabled by the advanced CW-OPO technologies will be presented. These examples include a demonstration of world-record detection sensitivity in trace gas analysis, as well as the first characterization of infrared spectrum of radioactive methane 14 CH4.

A widely tunable difference-frequency-generation laser for high-resolution spectroscopy in the 667–865 cm–1 range

“…However, cw-QCLs are limited to ~ 13 µm in wavelength and do not offer broad mode-hop-free tunability. In contrast, nonlinear frequency conversion based lasers, including optical parametric oscillation 8 and difference-frequency generation (DFG) 9 , provide broad tunability and can be designed to target specific MIR regions with wide spectral bandwidth and tunability 10 .…”