Two laser Doppler microscopes (LDMs) based on an optical heterodyne interferometer have been developed for measuring fluid velocity in a microchannel. One of LDMs receives light from a Zeeman laser, and one easily obtains the standard heterodyne signal because a polarizer is set in front of a photomultiplier tube. The other LDM, with light from a He-Ne laser, employs a diffractive grating as a frequency shifter that is modulated in a sinusoidal movement by a piezoelectric transducer stack. By this modulation the nonstandard heterodyne signal is further processed by a new synthetic heterodyne algorithm. Finally, the phase shift related to the fluid velocity in both LDMs is demodulated by digital postprocessing in fast-Fourier-transform, bandpass filtering, inverse-fast-Fourier-transform, and arctangent algorithms.
© 2002 Optical Society of America
(040.2840) Detectors : Heterodyne
(180.3170) Microscopy : Interference microscopy
(280.0280) Remote sensing and sensors : Remote sensing and sensors
(280.2490) Remote sensing and sensors : Flow diagnostics
(350.3950) Other areas of optics : Micro-optics
Yu-Lung Lo and Chi-Hsin Chuang, "Fluid Velocity Measurements in a Microchannel Performed with Two New Optical Heterodyne Microscopes," Appl. Opt. 41, 6666-6675 (2002)