Femtosecond ultraviolet laser absorption spectroscopy for simultaneous measurements of temperature and OH concentration

This Letter reports a femtosecond ultraviolet laser absorption spectroscopy (fs-UV-LAS) for simultaneous in situ measurements of temperature and species. This fs-UV-LAS technique was demonstrated based on X-2 pi-A(2)sigma(+) transitions of OH radicals near 308 nm generated in low temperature plasmas and flames. The fs-UV-LAS technique has revealed three major diagnostic benefits. First, a series of absorption features within a spectral bandwidth of ~& nbsp;3.2 nm near 308 nm were simultaneously measured and then enabled simultaneous multi-parameter measurements with enhanced accuracy. The results show that the temperature and OH concentration could be measured with accuracy enhanced by 29-88% and 58-91%, respectively, compared to those obtained with past two-narrow-line absorption methods. Second, an ultrafast time resolution of ~& nbsp;120 picoseconds was accomplished for the measurements. Third, due to the large OH X-2 pi-A(2)sigma(+) transitions in the UV range, a simple single-pass absorption with a 3-cm path length was allowed for measurements in plasmas with low OH number density down to ~& nbsp;2 x 10(13) cm(-3). Also due to the large OH UV transitions, single-shot fs absorption measurements were accomplished in flames, which was expected to offer more insights into chemically reactive flow dynamics. Published under an exclusive license by AIP Publishing.

Automated summary

This Letter reports a femtosecond ultraviolet laser absorption spectroscopy (fs-UV-LAS) technique for simultaneous in situ measurements of temperature and species. The fs-UV-LAS technique has three major diagnostic benefits, including simultaneous multi-parameter measurements with enhanced accuracy, ultrafast time resolution, and the ability to measure in plasmas with low OH number density and in flames with single-shot absorption measurements.