高校物理の波の分野で回折・干渉は重要な学習項目の一つである。本稿では光の干渉実験，光ディスクの干渉，・についての話題を提供する。いずれもすでによく知られている内容ではあるが，授業の参考になれば幸いである。

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Performance of the IDD, which is one kind of display device, has been improved. The IDD consists of a driving half mirror and a substrate mirror, which construct an interferometer. It is possible for the IDD to create all the colors of the rainbow in only one pixel. To realize the device, a parallel driving and a precise flatness are required for the driving mirror. To solve those problems, a new structure is proposed in this paper. With respect to the new structure, light interference in the pixel is caused by an optical path difference between the driving half mirror suspended by leaf-springs and a floating half mirror isolated electrically by SiO₂ layers. The driving mirror can be moved by the voltage applied between the driving mirror and a transparent electrode which is located under the floating mirror. This structure contributes to the removal of the hysteresis mirror movement, realization of stable driving and higher display contrast. By experiments using fabricated IDDs, improvements of interferometric characteristics and hysteresis property are confirmed.

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Theoretical background and experimental results of a direct measurement of frequency fluctuation of a freely running He-Ne laser output (0.6328μm) are given.
The He-Ne laser is designed and made for future use as a precision length standard. A tunable, confocal type, spherical mirror Fabry-Perot interferometer with a pass-band width of 7.5MHz is used as a frequency discriminator. The fluctuation of the laser frequency is analyzed by calculating the autocovariance and the power spectral density.
The results show that the amplitude of the fluctuatuion has several peaks at about 0.2, 2.5, and 5.8Hz and has a standard deviation of ±300kHz. It is considered that the frequency fluctuatuin is mainly caused by resonance vibration of the vibration-damping table on which the experimental system was set up, and by dynamic variation of the air pressure.

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In vibration sensing by use of a FBG based on intensity modulation, light incident on a FBG is narrow-band light tuned to the slope in a transmittance spectrum of the FBG. Since the sensor sensitivity is proportional to the slope of the spectrum curve, enhancement of the sensitivity requires steeper slope of the curve. In this paper, vibration sensing by use of Fabry-Perot interferometer with FBG reflectors (FBG-FPI) is numerically investigated. Because a transmittance spectrum of an FBG-FPI has steeper slope, the FBG-FPI can yield improvement in sensitivity of the sensing.

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