| 摘要 |
Single-crystal lithium tetraborate (single-crystal Li2B4O7 or single-crystal LBO) as an optical converter device which stably operates for a long term, has a long life, and is compact, light and inexpensive, an optical converter device using the single crystal LBO, especially, for emitting light having a wavelength of 500 nm or less, and an optical apparatus using the optical converter device. Coherent light irradiates the light incident face of the single-crystal LBO at a predetermined incident angle, which single-crystal LBO is cut at a predetermined plane to the optical axis in order to satisfy a predetermined phase matching angle, and light having a half wavelength of the incident light is emitted. Preferably, the single-crystal LBO has a refractive index variation of 10-5/mm or less and/or a etch-pit density of approximately 1x103/cm2. A first coherent light beam having a first wavelength and a second coherent light beam having a wavelength one-half or one-fourth of the wavelength of the first coherent light beam irradiates the incident face of the single-crystal LBO at a predetermined angle, and at least a coherent light having a wavelength one-third or one-fifth of the wavelength of the first coherent light beam is emitted by sum frequency generation, for example, when light having a wavelength of 209 nm is emitted, the wavelength of the first coherent light is 981 nm and that of the second coherent light is 266 nm.
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