Shock-tube measurements of excited oxygen atoms using cavity-enhanced absorption spectroscopy

摘要

We report the use of cavity-enhanced absorption spectroscopy (CEAS) using two distributed feedback diode lasers near 777.2 and 844.6 nm for sensitive, time-resolved, in situ measurements of excited-state populations of atomic oxygen in a shock tube. Here, a 1% O-2/Ar mixture was shock-heated to 5400-8000 K behind reflected shock waves. The combined use of a low-finesse cavity, fast wavelength scanning of the lasers, and an off-axis alignment enabled measurements with 10 mu s time response and low cavity noise. The CEAS absorption gain factors of 104 and 142 for the P-5(3) <- S-5(2)0 (777.2 nm) and P-3(0,1,2) <- S-3(1)0 (844.6 nm) atomic oxygen transitions, respectively, significantly improved the detection sensitivity over conventional single-pass measurements. This work demonstrates the potential of using CEAS to improve shock-tube studies of nonequilibrium electronic-excitation processes at high temperatures. (c) 2015 Optical Society of America