Quantitative dual-comb spectroscopy of titanium monoxide in laser-produced plasmas

The formation of titanium monoxide (TiO) following the laser ablation of a pure Ti metal sample is studied using dual-frequency comb spectroscopy (DCS). Time-resolved absorption measurements with high spectral resolution over a broad bandwidth allow for the quantitative characterization of the laser-produced plasma (LPP). This includes the evolution of Ti and TiO column densities and the determination of corresponding excitation and rotational temperatures through detailed analysis of absorbance spectra. DCS absorbance spectra were collected over a spectral bandwidth of 19070 cm⁻¹ to 19200 cm⁻¹ (520.83 nm to 524.38 nm) with measurement-limited resolution of 0.91 GHz (0.03 cm⁻¹, 0.83 pm), and from 30 µs to 80 µs after ablation. From the collected absorbance spectra, rotational temperature and column density measurements of TiO species were computed using rovibrational modeling of the C(³∆)–X(³∆) (0,0) band, and compared with the atomic Ti I excitation temperature and column density. The measurements were conducted in a vacuum chamber with an ambient background gas pressure of 200 Torr, under conditions with and without oxygen gas. An increase in the excitation temperature of the Ti atomic species was observed in the presence of TiO formation. Additionally, a distinct difference in the dynamics of measured atomic column densities between the two conditions was noted.