Lyot filter

Japanese: リヨ･フィルター（英語表記）Lyot filter

A birefringent interference filter invented by B. Lyot of France in 1933. It is used to capture monochromatic images of the sun because its transmission wavelength width is extremely narrow, at approximately 1 Å (0.1 nm) or less. As shown in the figure, light incident on a crystal plate such as quartz or calcite generates a phase difference between the ordinary and extraordinary rays, and by causing interference between these rays, a filter is formed in which the transmittance changes periodically with wavelength. The periodic change in transmittance varies depending on the thickness of the crystal plate, and the wavelength interval of the maximum transmission wavelength is inversely proportional to the thickness of the crystal plate for the same material, so stacking crystal plates with twice the thickness will result in a filter with a narrow transmission wavelength width.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

1933年フランスのB.リヨによって考案された複屈折干渉フィルター。透過波長幅が約1Å(0.1nm)以下と非常に狭いので，単色の太陽像を撮るのに使われる。図に示すように水晶や方解石などの結晶板に入射した光は，常光線と異常光線とで位相差を生じ，それを干渉させることにより，透過率が波長に対し周期的に変化するフィルターとなる。透過率の周期的変化は，結晶板の厚みにより異なり，透過極大波長の波長間隔は同じ材質では結晶板の厚さに反比例するので，厚さが2倍比の結晶板を重ね合わせると，透過波長幅の狭いフィルターとなる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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