| 摘要 |
PROBLEM TO BE SOLVED: To reduce instable oscillation such as multi-mode oscillation or mode hop by increasing the filter effect of wavelength in an external resonator type laser light source. SOLUTION: This external resonator type laser light source is provided with a semiconductor laser LD whose one edge face (1) is coated with a reflection preventing film and plural diffraction gratings GR1 and GR2 as wavelength selecting elements. In this case, outgoing lights from the edge face (1) coated with the reflection preventing film of the semiconductor laser are made incident with an angleαof diffraction, and lights with wavelengthγare allowed to outgo with an angleβof diffraction at a point A on the diffraction face of the first diffraction grating GR1. The lights with the wavelengthγoutgoing with the angleβof diffraction from the first diffraction grating GR1 are made incident with an angleγof diffraction, and allowed to outgo with the angleγof diffraction at a point B on the diffraction face of the second diffraction grating GR2, so that the lights can be returned along the opposite optical path from the second diffraction grating GR2 through the first diffraction grating GR1 to the semiconductor laser. Thus, an external resonator can be constituted of the edge face opposite to the edge face (1) coated with the reflection preventing film of the semiconductor laser and the second diffraction grating GR2.
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