In Holographic Particle Image Velocimetry (HPIV), the position of all the particles present at one instant of time is recorded on a holographic plate (double-exposure). The light scattered from the particle (~1 - 50 microns (in air)) is made to interfere with the reference laser beam and the interference effect is then recorded locally onto the holographic plate. A holographic imaging system generally requires that the reference beam should subtend an oblique angle with the scattered beam. This recording geometry is often referred as an off-axis holographic system. After the exposed hologram is developed, the particle images can be reconstructed with a reference beam playback system. Several millions of velocity vectors can be extracted from a good quality hologram. 
For high quality image reconstruction, the reference beam in playback ideally should have the same wavelength and wave front characteristics as the recording reference beam. This avoids problems of magnification and poor image contrast in the holographic records. Recently, the HPIV technique (side-scattered, reflection geometry) has been demonstrated successfully in an optical internal combustion engine.

Typical HPIV Equipments:

Double-pulsed Laser system (single longitudinal mode with good beam quality) with frequency stablisation system, seeding particles generator, optional CW laser (playback), holographic plates, plate holders, and holographic plate processing chemicals (eg. D19, GP62), dark room with safe light, mechanically stable optical workbench (vibration damped), optical flat, lenses, polarisers, mounts and posts, pinholes, good quality high energy mirrors (object laser beams), additional mirrors (0 and 45^o incident) for reference beams and object beams path length compensation, fibre optics (optional), neutral density filters, spatial filters,  power meters with CW or pulsed head adaptors, CCD camera, high performance computer (large memory and large capacity hard disk), CD burner for data storage, frame grabber card, D/A & A/D converter board, automated three-dimensional translation stages for data extraction from a hologram (HOE) and image processing software. Photopolymers and Bacteriorhodopsin do not require wet processing.

Holographic Recording Materials:

Silver Halide, Photopolymer, (BR) Bacteriorhodopsin, etc.

Commercial products: BR

In-cylinder holographic measurement

General Reference:

Barnhart, D.H., Adrian, R.J. & Papen, G.C., 1994. Phase conjugate holographic system for high resolution particle image velocimetry. Appl. Optics 33, pp.7159-7170.

Barnhart, D.H.,  Halliwell N. A. & Coupland, J. M., 2000. Holographic particle image velocimetry: analysis using a conjugate reconstruction geometry, Optics and Laser Technology Volume 32, Issues 7-8,
pp. 527-533

Coupland, J.M. & Halliwell, N.A., 1997. Holographic displacement measurements in fluid and solid mechanics: immunity to aberrations by optical correlation processing. Proc. R. Soc. Lond. A 453, pp.1053-1066.

Royer. H., 1997. Holography and Particle Image Velocimetry. Meas. Sci. Technol. 8, pp. 1562-1572.

Hinsch K.D., 2002. Holographic particle image velocimetry. Meas. Sci. Technol. 13 R61-72.

Hariharan, P.  1996.  Optical Holography: principles, techniques, and applications.  2nd Edition, Cambrigde University Press, ISBN 0-521-43348-7( Hardback), ISBN 0-521-43965-5 (Paperback).

Verdict and Comment:

A cutting-edge but technically demanding volumetric (truly global) flow measurement technology. Main interests are from a few research institutes (mainly in the US) and some specialised university laboratories in the world.

Additional link: bR and HPIV