Dual-comb Spectroscopy of Laser-Induced Plasmas*

Dual-comb spectroscopy (DCS) has found a broad range of applications thanks to its ability to provide high spectral resolution over a broad bandwidth. Many applications are based on quasi-static spectroscopic measurements such as those needed in remote sensing or LiDAR. We have been exploring the use of DCS to perform time-resolved measurements of laser-induced plasmas (LIPs). LIPs are powerful tools for the analysis of solid-state materials. For example, it has been used for forensic investigations and isotopic analysis of nuclear materials. A common spectroscopic technique utilizes emission from the LIPs, often referred to as laser-induced breakdown spectroscopy (LIBS). Emission studies generally probe early times in the plasma evolution and with limited spectral resolution.  We first applied DCS to LIPs as a proof of concept to detected trace amounts of Rb and K over 8 THz following a single laser ablation shot, with sufficient resolution to resolve the Rb D2 lines. We present more recent results demonstrating novel approaches for higher time-resolution, and multi-species measurements of ionic and atomic transitions, as well as molecular formation following oxidation of Ce within the plasma plume. The wealth of spectral information from this technique enables the characterization of the time-evolution of constituent number densities and plasma temperatures. We also demonstrate a new approach for the measurement of oscillator strengths, demonstrating assignments to 43 neutral gadolinium transitions.