Continuum laser absorption spectroscopy of C2(a3Πu) in a sublimating cloud of carbon black

A direct optical absorption diagnostic has been developed for rotationally resolved measurements of diatomic carbon (a³Π_u→d³Π_g (0,0) and (1,1)) at a repetition rate of 525 kHz and resolution of 7.3 pm over the range of 511.1–514.1 nm. The diagnostic utilizes a high-power pulsed continuum laser light source dispersed in a spectrograph and imaged by a high-speed camera. Measurements have been performed that capture the temporal evolution of C₂ number density and temperature of a cloud of carbon black sublimating in shock heated gas at high temperature and pressure (T = 5500 K, P = 3.7 atm). A simultaneous light absorption measurement of the condensed phase enables comparisons of the gaseous C₂ number density to the condensed phase mass. The continuum laser absorption diagnostic is applied to C₂ in this work but shows promise in being a simple “drop-in” system for absorption spectroscopy in the visible range at rapid repetition rates and high dispersion, filling an important gap for laser diagnostic systems.