Abstract: A silicon carbide single crystal includes: threading dislocations each of which having a dislocation line extending through a C-plane, and a Burgers vector including at least a component in a C-axis direction. In addition, a density of the threading dislocations having angles, each of which is formed by an orientation of the Burgers vector and an orientation of the dislocation line, larger than 0° and within 40° is set to 300 dislocations/cm2 or less. Furthermore, a density of the threading dislocations having the angles larger than 40° is set to 30 dislocations/cm2 or less.

Abstract: A silicon carbide single crystal includes: threading dislocations each of which having a dislocation line extending through a C-plane, and a Burgers vector including at least a component in a C-axis direction. In addition, a density of the threading dislocations having angles, each of which is formed by an orientation of the Burgers vector and an orientation of the dislocation line, larger than 0° and within 40° is set to 300 dislocations/cm2 or less. Furthermore, a density of the threading dislocations having the angles larger than 40° is set to 30 dislocations/cm2 or less.

Abstract: In a laser device having a solid-state laser medium of a slab or rod-shaped crystal, a flash lamp serving as an excitation-light source for the laser medium, and a reflector made of a foamed quartz glass for injecting light produced by the light source into the laser medium, an insulator made from a foamed glass is utilized to improve the efficiency of light injection and the resulting beam quality. In addition, where the laser medium is doped with Nd.sup.3+, a wavelength conversion filter made of a material doped with Cr.sup.3+ or Ti.sup.3+ is utilized to convert most of the excitation light into a wavelength most suitable for exciting the laser medium. Foamed quartz glass is preferred also as the material for the inner surface of an integrating sphere for optical measurement.

Abstract: In a laser device having a solid-state laser medium of a slab or rod-shaped crystal, a flash lamp serving as an excitation-light source for the laser medium, and a reflector made of a foamed quartz glass for injecting light produced by the light source into the laser medium, an insulator made from a foamed glass is utilized to improve the efficiency of light injection and the resulting beam quality. In addition, where the laser medium is doped with Nd.sup.3+, a wavelength conversion filter made of a material doped with Cr.sup.3+ or Ti.sup.3+ is utilized to convert most of the excitation light into a wavelength most suitable for exciting the laser medium. Foamed quartz glass is preferred also as the material for the inner surface of an integrating sphere for optical measurement.

Abstract: A solid state laser apparatus includes a laser medium of a uniaxial crystal, such as a fluoride crystal, having a negative temperature variation ratio of refractive index, laser diodes for optically pumping the laser medium, a set of mirrors positioned at two longitudinal ends of the laser medium for oscillating the light in the laser medium and outputting a beam, and a system for cooling the laser medium. The thermal lens effect is suppressed by causing a thermal gradient to exist along only one chosen axis of the laser medium and eliminating the thermal lens diopter along the chosen axis by optimizing a ratio L/D of length L and diameter D of the laser medium.

Abstract: An optical resonator which is unstable with respect to laser light whose wavelength is to be converted includes a pair of confocal, coaxial curved mirrors. A nonlinear optical medium, e.g., lithium niobate, is disposed between the mirrors. Laser light injected into the optical resonator becomes concentrated in the vicinity of the optical axis, for highly efficient wavelength conversion.

Abstract: A change in the wavelength of a laser beam is achieved by causing the beam to have a conical wavefront and applying it to a nonlinear crystal so that the beam converges along the center axis producing an output beam of a different wavelength. The conical wavefront is achieved in wavefront conversion means by use of lenses, mirrors and crystals with conical surfaces. Adjustability is provided by diverging the beam first and then converging it, with adjustment in the spacing between the divergence means and convergence means of a wavefront conversion means.

Abstract: In a high-efficiency solid-state laser device with an optical resonator including a solid-state laser medium in the form of a slab crystal, for example, a flash lamp serves as the excitation light source of the solid-state laser medium, and a reflector serves for injecting light produced by the light source into the laser medium. A reflector made of a foamed quartz glass has high diffusion reflectance over a wide range of wavelengths from the infrared to the ultraviolet. Foamed quartz glass is preferred also as an integrating sphere material for optical measurement.

Abstract: An optical resonator which is unstable with respect to laser light whose wavelength is to be converted includes a pair of confocal, coaxial curved mirrors. A nonlinear optical medium, e.g., lithium niobate, is disposed between the mirrors. Laser light injected into the optical resonator becomes concentrated in the vicinity of the optical axis, for highly efficient wavelength conversion.

Abstract: For high energy density and improved processing performance of a solid-state laser, the product .theta.d of a laser beam with divergence .theta. and beam diameter "d" at the beam waist is reduced. Formation of an non-oscillating region as in an output mirror with a pinhole is prevented by use of a hole-type mirror with a central region having reduced reflectance. For increased range of stable oscillation, a beam expander is interposed between a laser medium and the output mirror. The focused beam of a slab laser is made circular by using a columnar light-guiding path on the output side of the output mirror. A laser beam is more readily admitted into an optical fiber by use of a conical light-guiding path. With a hole-type output mirror, two-component laser output from a slab laser has very small .theta.d values.

Abstract: A change in the wavelength of a laser beam is achieved by causing the beam to have a conical wavefront and applying it to a nonlinear crystal so that the beam converges along the center axis producing an output beam of a different wavelength. The conical wavefront is achieved in wavefront conversion means by use of lenses, mirrors and crystals with conical surfaces. Adjustability is provided by diverging the beam first and then converging it, with adjustment in the spacing between the divergence means and convergence means of a wavefront conversion means.

Abstract: A change in the wavelength of a laser beam is achieved by causing the beam to have a conical wavefront and applying it to a nonlinear crystal so that the beam converges along the center axis producing an output beam of a different wavelength. The conical wavefront is achieved by use of lenses, mirrors and crystals with conical surfaces.

Abstract: An excimer laser apparatus with an HCl generator. The HCl generator is constructed so that HCl gas is generated by the reaction of a fixed concentration of hydrogen gas in the laser gas mixture with an equivalent amount of metallic chlorides. The reaction occurs at a preset temperature, and the metallic chlorides may be either in the laser gas chamber or in the circulation line of the laser gas. Consequently, the HCl required for laser generation is continuously formed by the H.sub.2 reduction of the metallic chlorides. The HCl loss due to the formation of impurities is automatically replenished to maintain a constant concentration of HCl in the laser gas, which results in stable laser generation. This simplified and dependable excimer laser apparatus can be operated continuously for a long time, since it is not necessary to measure and replenish the HCl lost due to the formation of impurities. Furthermore, instead of using a bomb for the highly toxic HCl gas, a bomb for He mixed with H.sub.