Molecular clocks for isotopic analysis

Femtosecond (fs) laser-induced molecular alignment is a powerful technology for orienting a randomly aligned ensemble of molecules along the laser beam polarization direction. Molecular alignment combined with appropriate detection allows for different species to serve as molecular clocks, with each of them rotating at different but well-defined frequencies. This feature is promising for improving gas detection selectivity. In this work, we use molecular alignment combined with Weak Field Polarization (WFP) for the detection of the isotopes of 12 C 16 O 2 and 12 C 18 O 2 . We demonstrate that 2D wavelength-resolved WFP signal acquisition, coupled with advanced 2D wavelength-time and wavelength-frequency analysis, provides complementary information over traditional wavelength-integrated WFP analysis. Information-rich datasets unveil distinct spectral-temporal and spectral-frequency grouping patterns which vary as a function of revival fraction increments for the isotopes of interest. These findings underline the potential of this method in enhancing gas phase detection selectivity for a variety of laboratory and future gas remote sensing applications.