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Cavity Enhanced Spectroscopy of High-Temperature H2O in the Near-Infrared Using a Supercontinuum Light Source

Watt R, Laurila T, Kaminski CF, Hult JF, "Cavity enhanced spectroscopy of high temperature H2O in the near infrared using a supercontinuum light source", Appl. Spectroscopy 63 (12), 1389-1395 (2009), doi:10.1366/000370209790108987 | pdf


Abstract

In this paper we demonstrate how broadband cavity enhanced absorption
spectroscopy (CEAS) with supercontinuum (SC) radiation in the nearinfrared
spectral range can be used as a sensitive, multiplexed, and simple
tool to probe gas-phase species in high-temperature environments. Nearinfrared SC radiation is generated by pumping a standard single-mode
fiber with a picosecond fiber laser. Standard low reflectivity mirrors are
used for the cavity and an optical spectrum analyzer is used for the
detection of gas-phase species in combustion. The method is demonstrated
by measuring flame generated H2O in the 1500 to 1550 nm region and
room-temperature CO2 between 1520 nm and 1660 nm. The broadband
nature of the technique permits hundreds of rotational features to be
recorded, giving good potential to unravel complex, convoluted spectra.
We discuss practical issues concerning the implementation of the
technique and present a straightforward method for calibration of the
CEAS system via a cavity ringdown measurement. Despite the large
spectral variation of SC radiation from pulse to pulse, it is shown that SC
sources can offer good stability for CEAS where a large number of SC
pulses are typically averaged.