The characteristics of a photographic emulsion as a hologram recording material are experimentally studied and reported. Two beam interference fringes with spatial frequency of 0-2700 lines/mm are recorded on Kodak 649F films and diffraction efficiency was measured before and after bleaching of the hologram. The linear recording range was found to be 1.3-1.9μW. sec/mm² for the unbleached hologram. The observation of diffraction efficiency agreed fairly well with the theoretical prediction in case of the hologram bleached with Hg Cl₂. The amount of phase modulation of the bleached hologram was measured and further separated into two components, a component due to surface relief and a component due to change of refraction index of emulsion. The surface relief reaches at its peak at spatial frequency of 30 lines/mm and maximum peak-to-peak of 1.5μ was obtained at 10μW sec/mm² mean exposure. The surface relief exists up to 1800 lines/mm. The amount of index modulation, the maximum peak-topeak value of which is about 0.05, does not change much over wide range of spatial frequency.

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The refractive index of a medium in the form of small sphere or cylinder was measured by a method based on the theory of rainbow. The principle of the method is based on the fact that the minimum deviation angle of rays reflected once internally depends solely on the refractive index of the sample. Experimental results confirm that the accuracy is of the order of unity in the second decimal place and improved by successive approximation.
This method is particularly suited to materials of high refractive index, because the conventional immersion method needs more refractory liquids which contain inevitably such poisonous element as As. The principle of the method and some experimental results are described.

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Experimental description of image recording by modulated laser beam is given. Image signal is modulated voltage to time converter. This produces optical pulses with duration controllable 0 to 480 nsec.
The repetition rate is 2 MHz. In addition to experiments along this line, another method using an amplitude modulation is reported.

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