Frequency converter and frequency conversion method with lithium tetraborate, and an optical device with this frequency converter

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 is irradiated to 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 so as 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 an etch-pit density of approximately 1×103/cm2. A first coherent light beam having a first wavelength and a second coherent light beam having a one-second or one-fourth wavelength of the first coherent light beam are irradiated to the incident face of the single-crystal LBO at a predetermined angle, and at least a coherent light having a one-third or one-fifth 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, for example.