Infrared planar laser-induced fluorescence with a CW quantum-cascade laser for spatially resolved CO2 and gas properties

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2015-08, Vol.120 (2), p.185-199
• Main Authors: Goldenstein, Christopher S., Miller, Victor A., Hanson, Ronald K.
• Format: Article
• Language: English
• Subjects: Engineering; Lasers; Optical Devices; Optics; Photonics; Physical Chemistry; Physics; Physics and Astronomy; Quantum Optics; Rapid Communication
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-015-6167-0

The design and demonstration of a new infrared laser-induced fluorescence (IR-LIF) technique that enables spatially resolved measurements of CO 2 , temperature, and pressure, with potential for velocity, are presented. A continuous-wave, wavelength-tunable, quantum-cascade laser (QCL) near 4.3 μ m with up to 120 mW was used to directly excite the asymmetric-stretch fundamental-vibration band of CO 2 for approximately 200 to 10 5 times more absorbance compared with previous IR-LIF techniques. This enabled LIF detection limits (signal-to-noise ratio of 1) of 20 and 70 ppm of CO 2 in Ar and N 2 , respectively, at 1 bar and 296 K in static-cell experiments. Simplified and detailed kinetic models for simulating the LIF signal as a function of gas properties are presented and enable quantitative, calibration-free, IR-LIF measurements of CO 2 mole fraction within 1–8 % of known values at 0.5–1 bar. By scanning the laser across two absorption transitions and performing a multi-line Voigt fit to the LIF signal, measurements of temperature, pressure, and χ CO 2 within 2 % of known values were obtained. LIF measurements of gas pressure at a repetition rate up to 200 Hz (in argon) are also presented. Planar-LIF (PLIF) was used to image steady and unsteady CO 2 –Ar jets at 330 frames per second with a spatial signal-to-noise ratio (SNR) up to 25, corresponding to a detection limit (SNR = 1) of 200 ppm with a projected pixel size of 40 μ m . The gas pressure was measured within 3 ± 2  % of the known value (1 bar) at 5 Hz by scanning the QCL across the P(42) absorption transition and least-squares fitting a Voigt profile to the PLIF signal. Spatially resolved measurements of absolute CO 2 mole fraction in a laminar jet are also presented.