title: Fluid velocity measurements in a microchannel performed with two new optical heterodyne microscopes.
abstract: 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.
authors.affiliation: Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan. loyl@mail.ncku.edu.tw
authors.forename: Yu-Lung
authors.initials: YL
authors.lastname: Lo
authors.forename: Chi-Hsin
authors.initials: CH
authors.lastname: Chuang