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By near-infrared spectroscopy, we classified water molecules in hydrated gelatin membranes in a drying process. Absorbance spectra in the frequency range of 4500–5500 cm−1 were resolved into three peaks, S0, S1, and S2, that correspond to water molecules with different hydrogen bond states. From the areas of the absorbance peaks as a function of the water content of gelatin, together with the information on the freezing properties of water measured by differential scanning calorimetry, we found that, when the water content is less than 20%, free water disappears and only weakly and strongly bound waters remain. We also found that the weakly bound water consists of S0, S1, and S2 water molecules with a simple composition of . Using this information, most of the freezable water was determined to be free water. Our classification provides a simple method of estimating the retention and freezing properties of processed foods or drugs by infrared spectroscopy.

The temperature and electric field dependences of the photorefractive effect in proton-exchanged (PE) waveguides formed on MgO-doped lithium niobate (LN) are investigated in detail for the first time. As a result, the photorefractive effect (optical damage) is found to be enhanced by the electric field applied to the waveguide. On the other hand, resistance to the photorefractive effect is markedly increased when the samples are heated at temperatures as high as 80°C. We should take these properties into consideration in designing optical devices such as electrooptic modulators and parametric devices.