Hiroshi Murotani

Submicrometer optical characterization of the grain boundary of optically active Cr3+ doped polycrystalline Al2O3 by near-field spectroscopy

Abstract Near-field fluorescent spectroscopy was used to characterize the grain boundary of Cr-doped polycrystalline alumina. The results show that the peak widths in near-field spectra are narrower than in spectra obtained by conventional microspectrometry, and this is attributed to the difference in spatial resolution of the two methods. The R-line peaks of Cr3+ fluorescence were observed to shift to a lower wavelength at the grain boundary compared to the bulk crystal, which is attributed to stress relief at the crystal boundary. This peak shift at the boundary decreases as a function of the time a polycrystal is annealed at 1700 °C.

Optical Characteristics of Al2O3 Ceramics Doped with Cr at High Concentrations Prepared by Extrusion Molding Process

Polycrystalline Al2O3 ceramics doped with Cr (sintered ruby) up to high concentrations (0.66, 0.76 and 0.97 wt%) were fabricated with an extrusion molding process using Al2O3 and Cr2O3 powders. It was found from absorption spectra that a high concentration of Cr ions was optically activated. The fluorescence spectrum of Cr ions in the sintered ruby corresponded to that of a single crystal.

Analysis of long-term internal stress and film structure of SiO 2 optical thin films

Recently, the demand for durability of optical thin films, which have long been used, has been growing as the performance of optical components improves. The stress of a film is an important parameter that is related to its adhesion. The electron beam (EB) and ion-assisted deposition (IAD) methods are widely used to fabricate optical thin films. However, there are few reports on long-term internal stress, despite the importance of this issue. Here we discuss the time dependence of the stress of SiO2 optical thin films in terms of optical characteristics in the infrared region. It was found that SiO2 thin films prepared by the EB and IAD methods exhibited compression stress. The Si-OH molecular bond was observed at around 930 cm(-1) in the Fourier transform infrared spectroscopy spectrum of the sample prepared by the EB method, which exhibited a large change in internal stress after an elapsed time. It is considered that this change in bonding was related to the decrease in the stress of the films.

Time dependence of internal stress and optical characteristics of SiO2 optical thin film

Recently, optical thin films have been increasingly needed in optical components. SiO2 is most frequently used as a low- refractive-index material of optical thin films. The stress of the film is an important parameter that relates to the adhesion of the film. However, the long-term time dependence of the stress has not been thoroughly discussed for SiO2 optical thin films. In this report, the time dependence of the stress of SiO2 optical thin film is discussed in terms of optical characteristics in the infrared region. The optical properties and the structure of SiO2 optical thin films deposited by vacuum deposition (using an EB) and ion-assisted deposition (IAD) were observed by FT-IR, XRD and SEM. The stress of SiO2 optical thin films was measured using an interferometer to determine the change in the substrate shape. The SiO2 thin films prepared by both vacuum deposition and IAD exhibited compression stress. Decreases in the stress of the films deposited by vacuum deposition were observed to continue for more than 1000 hours. This result is different from that of the conventional stress model in which the stress changes stop after about one week. The stresses of the films prepared by IAD were observed to change little. Optical absorption by Si-O bonds was observed at 1100cm-1. The change in bonds from Si-O to Si-OH was observed in the film deposited by vacuum deposition. It is thought that this result of the change in bonds was related to the decrease in the stress of the films.

Depositing highly adhesive optical thin films on acrylic substrates.

Optical thin films are used to control the reflectance and transmittance of optical components. However, conventional deposition technologies applicable to organic (plastic) substrates typically result in weak adhesion. We overcame this problem by using vacuum deposition in combination with sputtering to directly deposit a SiO2 optical thin film onto an acrylic resin substrate. We observed neither yellowing nor deformation. The hardness of the film is 2H as measured by the pencil hardness test, indicating successful modulation of optical properties without sacrificing substrate hardness.

Fabrication of microlens using CO2 laser and characterization of formation process

Microlenses were formed directly on a surface of a glass plate by using CO2 laser. This method has the merit of complete dry processing and presents simple way of microlens fabrication. We discuss about the formation process and mechanism through the characterization of irradiation parameters and the glass composition. When the surface of a glass plate is heated locally to a working point of the glass material by a focused CO2 laser beam, a microlens is formed owing to surface tension. It was found possible to fabricate microlens easily placed at different focal position by controlling a laser power and an irradiation time. The volume of the fabricated microlens was found to be dependent on laser irradiation energy (laser power x irradiation time) and irradiated position. When a Corning 7059 glass plate was used, a convex microlens was obtained at the energy density smaller than ca.100 (μJ/μm2 ). The dynamical stress change of the microlens was measured in-situ by using the ellipsometry analysis to make clear the formation process of microlens. The T-FDP (four detectors polarimeter of transmission type) was used for this analysis.

Metal nanolayer deposited highly stable Ag thin films and their optical properties

We have reported that deposition of several-nm-thick Al surface layer on Ag thin films improved thermal stability remarkably. In the present study, we investigated the influence of the deposition of Al nanolayer on the reflectance of the Al/Ag multilayer. 100-nm-thick Ag film and 1–5-nm-thick Al surface layer were deposited successively by vacuum evaporation, and their optical properties were measured. The reflectance of the samples on which a 1- or 3-nm-thick Al layer was deposited on the Ag film was almost the same as that of the Ag single-layer film. However, the samples on which a 5-nm-thick Al layer was deposited on the Ag film showed decreased reflectance. It was considered that the deposited Al nanolayer was fully oxidized in the former samples, but metallic Al and oxidized Al coexisted in the latter sample, which coincided with the simulated reflectance data. As a result, we revealed that thermally stable Ag films formed by 1- or 3-nm-thick Al nanolayer deposition have also high optical reflectance.

Development of laser scissors for carbon and silicon carbide fiber cutting

Laser cutting of carbon (C) and silicon carbide (SiC) fibers was performed using a second harmonic generation (SHG) sheet beam of Q-switched Nd:YAG laser with an out put energy of 4J/pulse, pulse width of 10ns and a fluence of 3.0J/cm2. The beam was irradiated respectively on monofibers of C and SiC placed on an optical glass slide in air at room temperature. A single pulse was irradiated every one second and repetition number of shot pulses N was varied from N=10 to 40 pulses. Cutting of C and SiC fibers occurred for N = 20-40 pulses. A cut portion of C fiber fixed on the substrate for one end in tension free was found to have very sharp wedge like profile. Laser irradiation for C fiber fixed with both ends on the substrate made the fiber fractured with thinner fiber diameter. Similar profile was also observed in a SiC fiber at the cut portion. Smooth flat surface of laser cut portion of C and SiC fibers suggested a laser ablation by evaporation. In the SiC fiber, sticky and viscous layer was observed at the cut surface, suggesting vitreous silica formed by oxidation of laser-irradiated fiber.

Preparation of Cr: Al2O3 ceramics with low scattering loss

The laser medium made of a single crystal is generally limited in several factors to fabricate large size crystals and to dope optically active elements heavily. For the improvement of these factors, it is proposed to use ceramics for the laser. We have succeeded to fabricate highly transparent ceramics ruby by using CIP and vacuum sintering techniques. The fluorescence spectrum of Cr ions in the ceramics ruby corresponded to that of a single crystal.

Stress Control of an Optical Thin Film by Sputtering and Vacuum Deposition

Deposition of SiO2 by simultaneous sputtering and electron beam vacuum deposition resulted in a stress of various values thin films.