Some laser interferometers for use in fluid mechanics

The design of interferometers for use in aerodynamic research has been determined partly by the need to use short exposure times. Very bright light is essential, and with normal sources this means that the source must have appreciable size and spectral bandwidth. This leads to many restrictions on the design of the interferometer. The present paper shows that with laser sources these restrictions may be removed. Several appropriate designs are discussed, some being simplified versions of types already in use while others have not previously been described. All depend for their success on the coherence of the laser light source.