Anisotropic response of a silver chloride emulsion printed out by linearly polarized achromatic signal

Abstract

We describe the anisotropic response of a silver chloride photographic emulsion after exposure to a linearly polarized achromatic signal. As it is described in previous papers, such a plate is a uniaxial medium with its optic axis parallel to the direction of the light vibration that induced anisotropy. It exhibits dichroism and birefringence, which are respectively equal to zero for two wavelengths independently of the exposure time. We calculate the refractive and absorption indices of such a colloidal medium following a method proposed by Garnett in 1905. The medium is assumed to be formed by three kinds of particles: silver chloride isotropic particles, silver isotropic particles generated by the action of linearly polarized short wavelengths on the silver chloride, and ellipsoidal silver particles resulting from the partial destruction of the previous ones by the linearly polarized long wavelengths. Finally, the amplitude response of the plate consists of two terms: an isotropic term that characterizes the isotropic darkening of the plate, which decreases linearly when exposure increases, and a term, which is proportional to the square of the exposure, that characterizes the anisotropic bleaching of the plate. Finally, we investigate the polarity of the signal reconstructed from the anisotropic recording of a black-and-white transparency. We show that the polarity is always the same as that of the original object, whatever the wavelength of the reading beam may be, when the plate is observed between crossed polarizers.