QCL frequency stabilization and measurement with 100 Hz - level linewidth, drift and inaccuracy, using a robust upconversion technique

The mid-infrared (MIR) spectral range (λ > 4.5 µm) is of interest in both applied and fundamental spectroscopy, for diverse applications such as trace gas detection and molecular frequency metrology. Approaches currently pursued for enabling MIR spectroscopy with accurate frequency control are based on generating the desired radiation by down-conversion, either of frequency combs or of cw near-infrared (NIR) sources. Such downconverted sources, however, typically have low power per frequency interval.