Yoshiyuki Asahara

Gradient-index rod lens made by a double ion-exchange process.

Gradient-index rod lenses with a parabolic-index profile have been fabricated by a double Na-Ag ion-exchange process, and their optical characteristics have been evaluated. The numerical aperture and minimum focused spot diameter of the 2-mm diam rod lens were 0.58 and 2.5 microm for lambda = 0.63 microm, respectively. Because of the high diffusing rate for Ag ions, this technique offers the possibility of making large-sized (larger than 10 mm-diam) rod lenses for photographic uses.

Non-linear glass materials

Abstract Two types of composite glass are of current interest as non-linear materials. One is glass doped with semiconductor microcrystallites. Their non-linearities mainly originate from quantum confinement and band filling effects and now are on the order of 106 esu as a result of the progress in new glass fabrication technologies. The non-linear time response is limited to 100 ps because of the existence of trap levels in the microcrystallites. Photo-annealing effects are now being intensely studied for a modification of the response time. The second type is glass doped with small metal particles. Their non-linearities originate from local field and hot electron effects in the metal particles. The non-linear response time is shorter than several ps. The non-linear susceptibilities are on the order of 10−12 esu, because of the very low volume fraction of the metal particles. The non-linear optical properties of these composite glasses are reviewed in this article.

Glass waveguide laser

A channel waveguide fabricated in a Nd/sup 3+/-doped laser glass by the ion exchange method is discussed. The device was end-fire pumped by a diode-laser operating at 802 nm. Continuous-wave (CW) lasing was observed at 1054 nm, and maximum output power was higher than 150 mW. The large output power was achieved by increasing the radius of the waveguide.<<ETX>>

One-directional gradient-index slab lens

A gradient-index slab lens (2.5–3.4 mm thick) with parabolic-index profiles along the direction of thickness has been fabricated by a molecular stuffing process, and its refractive-index profiles have been evaluated.

Gradient-index slab lens with high numerical aperture.

A near-parabolic profiled 1-D lens with high N.A. (=0.70) has been fabricated by an indiffusion ion exchange and cementing technique. Maximum longitudinal aberration is lower than 0.2 mm all over the lens thickness. The focused beamwidth is ~5 μm.

The properties of gradient index antireflection layer on the phase separable glass

Abstract Gradient refractive index antireflection layer are produced by chemical leaching process applied to the phase separable glass. The reflection is lower than 0.5 % in the regime 0.4 – 1.4μ. Using a single inhomogeneous film model, the gradient index profiles are estimated from the reflection curves. Refractive index of the layer at the glass side is equal to that of the glass, while refractive index at the air side rapidly decreases with leaching time and becomes 1.09 at 6 minutes. More flat and lower reflection curve are obtained for the samples leached in the solution of the mixture of NH4F.HF and HNO3.

Memory effect in CuAsSe glasses containing small amounts of Au

Abstract The Cu, As and Se contents of Au-containing CuAsSe glasses significantly affected both the resistivity in the memory state and the time required to reach the memory state, whereas the Au content affects only the latter. The main crystalline species formed in these glasses was a CuAsSe compound, and its formation was enhanced by the addition of Au. The role of Au in the memory effect was discussed on the basis of crystallization behavior of glasses.

Optical glass wave plates

Permanent birefringence in excess of 300 nm/cm can be thermomechanically induced in the borosilicate optical glass ARG-2, making it an attractive alternative to natural crystalline quartz and mica for large-aperture wave-plate requirements in laser systems investigating inertial confinement fusion. The technique for fabricating glass wave plates is presented, including a detailed optical characterization of the uniformity of birefringence induced in glass plates. A comparison with other natural and synthetic candidate materials is made, and production scale-up problems are discussed.

Sensitivity of the photo-darkening effect in CuAsSe glasses

Abstract When CuAsSe glasses are irradiated, they exhibit higher concentrations of darkening than AsSe glasses. Since darkening depends on the composition, the darkening centers in CuAsSe glasses to be of the same kind as those in AsSe glasses, i.e. arsenic clusters. Concerning the kinetics of erasing, it was found that the activation energy and the rate constant of erasing in CuAsSe are almost equal to those in AsSe glasses, but for the kinetics of darkening, it was found that the activation energy of darkening is equal to that of AsSe but α 0 , which is proportional to the number of latent darkening centers, and the darkening rate constant k 1 are about twice as high as the corresponding constants of AsSe glasses. This may be the reason for the greater darkening in CuAsSe glasses. The high value of α 0 was attributed to the generation of more AsAs bonds on the addition of Cu to the AsSe glass network. The high value of k 1 was attributed to the increase in efficiency of photo-decomposition because of the many impurity levels in the band gap and also because of the narrow optical energy gap in the CuAsSe glasses.

ESR studies of semiconductor-doped glasses☆

Electron spin resonance of semiconductor-doped phosphate glasses has been measured at 77 K. Three types of signal are induced with precipitation of semiconductor nanocrystals in glass host materials. Two of them are attributed to glass defects around semiconductor nanocrystals and the other to S vacancies in CdS nanocrystals. The increase in electron spin resonance absorption with Ar-ion laser irradiation reveals that carriers photoexcited in nanocrystals are trapped not only on nanocrystal defects but also glass defects.