| 摘要 |
PURPOSE:To facilitate control of the width of a spectral line, by providing a reflection type filter, which feeds back rear emitting light of a laser to the laser, at a distance that is integer times the wavelength to be selected among laser light rays, and forming an external cavity. CONSTITUTION:Any of laser light rays having a plurality of wavelengths from a laser device 2 is selectively reflected by a reflection type filter 8. For example, the distance between the laser device 2 and the reflection type filter 8 is set at the length integer times the central wavelength of the laser light rays, and the light ray is reflected. With respect to only this reflecting component, the phase of the laser light, which is inputted into the laser device 2 from an external cavity 13 formed with the laser device 2 and the reflection type filter 8, is optimized, and oscillation occurs. Said component is made to be the laser light, which is outputted from the laser device 2. Namely, the laser light having the single wavelength is obtained. The width of the spectral line of the laser light having the single wavelength can be made narrow by the extension of the distance. When the setting conditions are misaligned, the conditions are recovered with an optical pathlength adjusting means 10.
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