title: Shock-tube measurements of excited oxygen atoms using cavity-enhanced absorption spectroscopy.
abstract: 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% O2/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 μs time response and low cavity noise. The CEAS absorption gain factors of 104 and 142 for the P35←S520 (777.2 nm) and P0,1,23←S310 (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.
authors.forename: Marcel
authors.initials: M
authors.lastname: Nations
authors.forename: Shengkai
authors.initials: S
authors.lastname: Wang
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Goldenstein
authors.forename: Kai
authors.initials: K
authors.lastname: Sun
authors.forename: David F
authors.initials: DF
authors.lastname: Davidson
authors.forename: Jay B
authors.initials: JB
authors.lastname: Jeffries
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Hanson