A method and apparatus for performing simultaneous multi-point
measurements of multiple velocity components in a gas flow is described.
Pulses of laser light are directed to a measurement region of unseeded
gas to produce Rayleigh or Mie scattered light in a plurality of
directions. The Rayleigh or Mie scattered light is collected from
multiple directions and combined in a single collimated light beam. The
Rayleigh or Mie scattered light is then mixed together with a reference
laser light before it is passed through a single planar Fabry-Perot
interferometer for spectral analysis. At the output of the
interferometer, a high-sensitivity CCD camera images the interference
fringe pattern. This pattern contains the spectral and spatial
information from both the Rayleigh scattered light and the reference
laser light. Interferogram processing software extracts and analyzes
spectral profiles to determine the velocity components of the gas flow at
multiple points in the measurement region. The Rayleigh light rejected by
the interferometer is recirculated to increase the accuracy and the
applicability of the method for measurements at high temperatures without
requiring an increase in the laser energy.