| 摘要 |
PURPOSE:To measure a fine temperature difference by arranging two crystals which have optical anisotropy in the directions of orthogonal (a) and (b) axes and are equal in length in the (c)-axial direction perpendicular to said axes. CONSTITUTION:Light from a light source 1 is polarized by a polarizer 2 into linear polarized light, which is incident along the (c) axis at 45 deg. to the orthogonal optically anisotropic axes (a) and (b) of a crystal element 3 to become elliptic polarized light. Then when it is incident on a crystal element 4, a phase difference is generated between its crystals. This elliptic polarized light passes through a phase modulating element 5 to become phase-modulated elliptic polarized light, which enters a 1/4 wavelength plate 6; and an analyzer 7 imposes intensity modulation and a photodetector 8 generates an AC signal of modulation frequency, so that its component and phase difference vary with the phase difference of the optical path. This signal is inputted to a phase detector and amplifier 9 and then its output is zero when the phase difference of the optical path is pi, thereby obtaining a positive or negative voltage signal according to whether the phase difference is large or small. This is returned to the element 5 to measure the level of the signal, and consequently the phase difference of the optical path which is smaller than pi is accurately obtained to know the temperature difference between the two crystals from the phase difference, so that when the temperature of one crystal is made constant, the temperature of the other crystal can be measured.
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