Increment threshold has been used as an index of representing brightness of background light or the response in the visual system caused by the background light. It is known qualitatively however, that increment threshold is not always equivalent to brightness when the background light is not uniform. To investigatge the effect of the nonuniformity of the background field upon the increment threshold, we measured the increment threshold distribution on step patterns and compared it with the increment threshold corresponding to the brightness on the step patterns. The difference was clearly observed, particularly at edges of the step patterns such that the measured increment threshold was larger than the increment threshold corresponding to brightness. It is suggested that the increment threshold is not always a good index of brightness of the light stimulus when the stimulus has a non-uniform distribution of luminance.

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Using the angular-spectrum representation of beam fields we have calculated Gaussian beams transmitted through tilted plane-parallel plates. An expression for power transmittance of incident beams having finite beamwidth and non-planar wavefront is derived by the use of the angular-spectrum representation of incident beams and shown to be in good agreement with experimental results for the Gaussian beam incidence. Performances of tilted etalons as mode selector are also theoretically analysed.

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Thermoplastic recording media possess many advantages over other holographic recording materials, such as high diffraction efficiency, erasability, etc. However, conventional thermoplastic recording techniques have several defects, one of which is thermal deformation of the substrate glass due to the heat which is used to soften the thermoplastic layer, and this causes distortions of the hologram. This paper proposes a new method for holographic recording by using a solvent vapour instead of heat to soften the thermoplastic. A number of experiments using this method were carried out, and several important advantages, such as non-critical development, no harmful effect of ambient temperature, no thermal deformation, etc, were found. These features suggest that this method may be highly recommended for real-time holographic interferometry.

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