NTECARS: A Nonthermal Equilibrium CARS Spectra Fitting Code

ABSTRACT

In this work, we present NTECARS, an open‐source code written in the programming language Julia for the calculation and fitting of single and dual‐pump CARS spectra under nonequilibrium conditions. The code enables flexible modeling and fitting of the rovibrational distributions using multitemperature models, models that do not require assumptions about the vibrational distribution or user‐defined distribution functions. NTECARS accounts for collisional narrowing effects, and convolutions with arbitrary laser and instrumental profiles, and allows for a wide range of parameters such as the molar fractions, instrumental profiles, and baseline offsets to be obtained through fitting. At present, and are fully implemented, with a modular design that allows for the inclusion of additional species without structural changes. The code is validated under thermal equilibrium conditions using both synthetic and measured spectra. The nonequilibrium capability is demonstrated by time‐resolved CARS measurements on a nanosecond‐pulsed discharge in a mixture and excellent agreement with time‐resolved absorption spectroscopy measurements from a previous work is found.