Bragg cell laser intensity modulation: effect on laser Doppler velocimetry measurements.
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.
Mychkovsky
Alexander G
AG
Department of Mechanical Engineering, University of Michigan, Ann Arbor, 1231 Beal Avenue, 2010 Auto Lab, Ann Arbor, Michigan 48109, USA. almych@umich.edu
Chang
Natasha A
NA
Ceccio
Steven L
SL