| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem of a laser beam although emitted from a semiconductor laser 11 can be suppressed, the spread of a spectrum being unable to be suppressed and a laser beam having a thin spectral bandwidth being unobtainable. SOLUTION: In order to generate a laser beam, having the thin spectral bandwidth from the semiconductor laser 11, a confocal FP resonator 13 or a dielectric multilayer-film filter 18 receives back light from the semiconductor laser 11. Then, the light of a prescribed wavelength is discriminated from the back light, and only the light of prescribed wavelength is returned to the semiconductor laser 11.
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