Towards doppler-free spectroscopy of O3 isotopes at 28 THz with a quantum cascade laser locked to a stabilized frequency comb reference

Quantum Cascade Lasers (QCLs) in the mid-IR range have become now suitable devices for ultra-high resolution laser spectroscopy, molecular trace gas sensors and the study of the possible time dependence of fundamental physical constants. We present here systematic studies of ozone molecular lines using Doppler absorption spectroscopy over a 1.6 cm⁻¹ mode-hop free tuning frequency range of a DFB-QCL centered around 1049 cm⁻¹. We apply controllable non-linear corrections on the current waveform driving the laser frequency. The resulting effect is a very efficient linearization of molecular spectra over the full current ramp, leading to a residual error in frequency below 2 × 10⁻⁴ cm⁻¹ over the entire spectrum (< 2 × 10⁻⁷). The free running laser spectrometer is coupled to two single pass absorption cells, arranged in a parallel setup, which allows for the study of pressure induced line shifts. First experimental pressure shift measurements for individual ozone absorption lines are reported. We also present our emerging project to stabilize the QCL source on an optical frequency-comb using experimental techniques for efficient non linear frequency conversion between IR and Telecom wavelengths.