Spectral and imaging properties of uniform diffusers

The use of thin phase diffusers in coherent imaging systems is analyzed. A condition is derived that must be fulfilled to ensure that no part of incident light is specularly transmitted. This condition is expressed in terms of first-order statistics of the phase of light emerging from a diffuser. It is shown that random diffusers whose amplitude-transmittance argument (phase) is uniformly distributed in the (−π, π) interval do not pass the specular light while their rms phase corresponds to only 0.29 of a wavelength. Such diffusers will be called uniform ones. A method for forming a uniform diffuser is proposed. It is based on a recording of normal speckle patterns in phase-photosensitive materials with consideration of the exposure characteristics. Autocorrelation functions and power spectra of diffuser transmittance are evaluated for two types of exposure characteristics. For both these cases the image contrast of the uniformly illuminated diffuser is calculated.