The classic laser-Doppler signal has a pronounced Gaussian envelope. This type of signal limits the useful demodulation time to the central portion of the signal where the amplitude is large. The problem could be alleviated by tailoring the intensity distribution throughout the measuring volume. It is well-known that the illuminating function and its image in the focal plane form a Fourier transform pair. In this case, if one wants to obtain a square wave intensity distribution in the object plane, the illumination function should be of the form sin x/x. However, an illuminating function of this type is not easy to produce.

© 1982 Optical Society of America

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