A moving diffuser destroys the spatial coherence of laser light only partially when the integration time is finite; this can be expressed by the signal-to-noise (S/N) ratio in the observed illuminance, due to the residual speckle. The method can be improved by the use of a two-diffuser system of which one diffuser is motionless, the other moving. In this case, the integration time (or the displacement of the diffuser) required to obtain a given S/N ratio can be greatly reduced, allowing the use of a slowly moving diffuser. Moreover, the S/N ratio does not depend on the optical-system parameters, whereas it depends on these parameters when a single diffuser is used.
© 1971 Optical Society of America
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