Beam misalignments and fluid velocities in laser-induced thermal acoustics

S Schlamp; E B Cummings; H G Hornung

doi:10.1364/ao.38.005724

Beam misalignments and fluid velocities in laser-induced thermal acoustics

Appl Opt. 1999 Sep 20;38(27):5724-33. doi: 10.1364/ao.38.005724.

Authors

S Schlamp¹, E B Cummings, H G Hornung

Affiliation

¹ Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, California 91125, USA. stefan@galcit.caltech.edu

PMID: 18324083
DOI: 10.1364/ao.38.005724

Abstract

Beam misalignments and bulk fluid velocities can influence the time history and intensity of laser-induced thermal acoustics (LITA) signals. A closed-form analytic expression for LITA signals incorporating these effects is derived, allowing the magnitude of beam misalignment and velocity to be inferred from the signal shape. It is demonstrated how instantaneous, nonintrusive, and remote measurement of sound speed and velocity (Mach number) can be inferred simultaneously from homodyne-detected LITA signals. The effects of different forms of beam misalignment are explored experimentally and compared with theory, with good agreement, allowing the amount of misalignment to be measured from the LITA signal. This capability could be used to correct experimental misalignments and account for the effects of misalignment in other LITA measurements. It is shown that small beam misalignments have no influence on the accuracy or repeatability of sound speed measurements with LITA.