In most laser Doppler velocimetry (LDV) systems, the frequency of one of the two laser beams that intersect to create the probe volume is shifted with an acousto-optic element. It is shown here that Bragg shifting can impose a problematic fluctuation in intensity on the frequency-shifted beam, producing spurious velocity measurements. This fluctuation occurs at twice the Bragg cell frequency, and its relative amplitude to the time average intensity is a function of the ratio of the laser beam diameter to the Bragg cell acoustic wavelength. A physical model and a configuration procedure to minimize adverse effects of the intensity modulations are presented.
© 2009 Optical Society of America
Instrumentation, Measurement, and Metrology
Original Manuscript: April 28, 2009
Manuscript Accepted: May 27, 2009
Published: June 12, 2009
Alexander G. Mychkovsky, Natasha A. Chang, and Steven L. Ceccio, "Bragg cell laser intensity modulation: effect on laser Doppler velocimetry measurements," Appl. Opt. 48, 3468-3474 (2009)