Noise reduction in coherent systems

Abstract

A method of producing coherent radiation signals which have reduced coherent noise content. The method involves modulation of the position of an apodizer or aperture disposed in the optical path of the radiation provided by the coherent radiation source. The modulation causes diffraction patterns created by the apodizer or aperture to be unstable, hence reducing the noise content of the transmitted radiation. In particular, a method of producing holographic exposures containing reduced coherent noise content is disclosed. The positions of apertures or apodizers utilized in producing the holographic exposure are modulated during the exposure process. The modulation is on the order of wavelengths of the illuminating radiation used to produce the exposure. The position modulation creates a slight fogging of the exposure due to the noise, but the desired hologram is recorded with little or no decrease in efficiency. Also, a method of producing an apodizer for use in generating the holographic exposure is disclosed. During preparation of the apodizer, it is modulated in position with respect to the illuminating radiation. The position is modulated on the order of wavelengths of the illuminating radiation. The modulation procedure reduces the noise content of the apodizer.