On-chip mid-infrared dispersive wave generation at targeted molecular absorption wavelengths

Abstract

The mid-infrared wavelength region is one of the most important spectral ranges for a variety of applications in monitoring and controlling molecules due to the presence of strong characteristic absorption modes of many molecules. Among various mid-infrared light sources, on-chip supercontinuum sources have garnered significant attention for their high spatial coherence, broad spectral bandwidth, compact size, and dispersion controllability. However, generating a supercontinuum that extends into the molecular fingerprint region typically requires high-energy mid-infrared pump pulses from complex optical systems. In contrast, supercontinuum generated with 1550 nm pump sources, which are generally more compact, has shown limited access to the molecular fingerprint region. In this study, we developed an on-chip supercontinuum source with a dispersive wave generated at a targeted wavelength of up to 4800 nm using a coupled pump energy of about 25 pJ. The pump pulses at a wavelength of 2340 nm were generated from a relatively compact Cr:ZnS laser oscillator. The wavelengths of the generated dispersive waves closely matched the numerically predicted wavelengths. To demonstrate the applicability of the generated dispersive waves for spectroscopic purposes, molecular absorption spectroscopy was performed on the fundamental vibrational modes of 12CO2, 13CO2, and N2O. In addition, their pressures were quantitatively estimated using cepstrum analysis on the measured absorption spectra. The uncertainty in the measured pressure was close to the theoretical limit determined by the uncertainties in the absorption line shape parameters in the HITRAN database, demonstrating the potential of this mid-infrared light source for advanced spectroscopic applications.