Citation:
Helen D. Ford, David S. Nobes and Ralph P. Tatam. Acousto-optic frequency switching for single-camera planar Doppler velocimetry. Proceedings of the SPIE Optical Diagnostics for Fluids, Solids, and Combustion. 31 July - 2 August 2001, San Diego, CA, USA. Volume 4448, 272. Eds. Carolyn R. Mercer, Soyoung S. Cha, Gongxin Shen
Abstract:
A single-camera Planar Doppler velocimetry system has been demonstrated, in
which illumination beams at two closely-spaced optical frequencies are derived
from a single Argon-ion laser. The frequency of one beam lies on an absorption
line of iodine vapour, and the other just off the absorption line. The beams
sequentially illuminate a plane within a seeded flow and the Doppler-shifted
scattered light passes through an iodine cell onto a single solid-state camera.
Light scattered from the measurement plane from the beam with its wavelength set
to be off the absorption line is not affected by its passage through the cell,
and provides a reference image, while that from the beam on the absorption line
encodes the velocity information as a variation in transmission dependent upon
the Doppler shift. The complex imaging system required for conventional PDV is
eliminated, since superposition of the reference and signal images is automatic.
The two beams are generated by an optical arrangement incorporating an acoustio-
optic modulator, and are transmitted to the region of interest by a single mode
optical fibre, which ensures both a smooth Gaussian illumination profile and co-
linearity of the beams. The system is demonstrated using a spinning disc and a
velocity resolution of +/-1 ms-1 is achieved.
