Dual-comb spectroscopy of laser-induced plasmas

Abstract

Dual-comb spectroscopy has become a powerful spectroscopic technique in applications that rely on its broad spectral coverage combined with high frequency resolution capabilities. Experiments to date have primarily focused on detection and analysis of multiple gas species under semi-static conditions, with applications ranging from environmental monitoring of greenhouse gases to high-resolution molecular spectroscopy. Here, we utilize dual-comb spectroscopy to demonstrate broadband, high-resolution, and time-resolved measurements in a laser-induced plasma. As a demonstration, we simultaneously detect trace amounts of Rb and K in solid samples with a single laser ablation shot, with transitions separated by over 6 THz (13 nm) and spectral resolution sufficient to resolve isotopic and ground state hyperfine splittings of the Rb D2 line. This new spectroscopic approach offers the broad spectral coverage found in the powerful techniques of laser-induced breakdown spectroscopy (LIBS) while providing the high-resolution and accuracy of cw laser-based spectroscopies.

Time-resolved mid-infrared dual-comb spectroscopy

“…In a first demonstration, DCS was used for measuring molecular free induction decay in the near-infrared (near-IR) wavelength range using two Er:fiber mode-locked lasers 27 . A few other works have been reported in near-IR region using Ti:sapphire mode-locked lasers including dual frequency comb-based transient absorption (DFC-TA) spectroscopy for measurement of the relaxation processes of dye molecules in solution from femtosecond to nanosecond timescales 28 , and DCS for the study of laser-induced plasma from a solid sample, simultaneously measuring trace amounts of Rb and K in a laser ablation 29 . Er:fiber mode-locked lasers has also been used in time-resolved dual-comb spectroscopy (TRDCS) to monitor a fast, single shot reaction 30 and also in continuous-filtering Vernier spectroscopy for combustion analysis 31 both with milliseconds time scale resolution.…”

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in a Plasma Using a Mid-Infrared Dual-Comb Spectrometer

“…To observe dissociation of ethane and formation of methane at different power levels, we measured the absorbance and phase changes by increasing the current density from 0 to 2.12 mA/mm 2 . Figure 11 shows the absorption spectra at different discharge current densities, demonstrating the ethane dissociation and the subsequent recombination of radicals forming methane as given by three-staged reaction in Equations (12)- (14). Different spectra are given a vertical offset for clarity.…”

“…To characterize the plasma process and maximize the conversion efficiency, various molecular species and reaction processes have to be measured and monitored during plasma operation. For this, methods are employed based on mass spectrometry [10] and optical detection, for the latter, specifically emission/absorption spectroscopy [11][12][13][14][15]. The main advantage of optical-based detection is their fast response time, in-situ measurement, and species specificity.…”

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer

“…To characterize the plasma process and maximize the conversion efficiency, different molecular species and reaction processes should be measured and continuously monitored during the plasma operation. Different methods are employed for this purpose, which are mostly based on mass spectrometry [10] or various in-situ optical detection techniques, such as emission and absorption spectroscopy [11][12][13][14][15]. The main advantages of the optical-based diagnostics over the other methods are their fast response time, in-situ measurement, and species specificity.…”