Accuracy And Uncertainty Of Single Shot Non Resonant Laser Induced Thermal Acoustics

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ISBN 13 :
Total Pages : 11 pages
Book Rating : 4.:/5 (227 download)

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Download or read book Laser-Induced Thermal Acoustics (LITA): Four-Wave Mixing Measurement of Sound Speed, Thermal Diffusivity, and Viscosity written by and published by . This book was released on 1994 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laser-induced thermal acoustics (LITA) is a promising optical four- wave mixing technique for gasdynamic measurement. The X(3) nonlinear process is a sequence of two opto-acoustic effects, electrostriction and absorption/rapid- thermalization, and the acousto-optic effect. The evolution of the laser-induced acoustic structures temporally modulates X(3) and thereby the LITA signal. Time resolution of the signal provides the sound speed, thermal diffusivity, and acoustic damping rate, along with information about atomic or molecular energy transfer rates. LITA can also measure spectra of both the real and imaginary gas susceptibility. The physics of LITA is discussed and the derivation is sketched of a simple analytical expression that accurately describes both the magnitude and time history of the LITA signal. Early experimental results are presented. Sound speeds accurate to 0.5% and transport properties accurate to 30% have been measured in a single-shot without calibration. More realistic modeling should dramatically improve transport-property measurement. LITA spectra have been taken of weak spectral lines of NO2 in concentrations less than 50 ppb. Signal reflectivities as high as 0.0001 have been estimated. New applications of LITA, including velocimetry, are suggested. LITA, Four-wave mixing, Thermal grating, Single-shot measurement, Velocimetry.