Fabrication of a laser cavity mirror in a large mode area fiber by an ultrashort pulse laser.

We present herein a method to fabricate a higher-order fiber grating (HOFG) for use as a fiber-cavity mirror in a fiber laser. The HOFG was fabricated by irradiating the Yb-doped large core of a double-clad fiber by a femtosecond pulsed laser. The HOFG served as a laser cavity mirror with a reflectance of 13.2% and yielded a laser line with a spectral full width at half-maximum of 0.56 nm.

Stress control in optical thin films by sputtering and electron beam evaporation.

It is necessary to control the internal stress of optical thin films in order to address problems such as peeling and cracking. Internal stress differs among films prepared by different deposition methods. We investigated the internal stress of films prepared by sputtering, electron beam (EB) evaporation, and a combination deposition method that we developed. The internal stress was successfully controlled, showing a value between that of EB evaporation and sputtering.

Long-term time dependence of internal stress in lanthanum titanium oxide (H4) optical thin films.

The time variation in the internal stress of optical thin films composed of lanthanum titanium oxide (H4) deposited by ion-beam assisted deposition (IAD) and electron beam deposition was observed over a period of 10 years after deposition, and it was found that the internal stresses in the optical thin films can be controlled by optimizing the IAD conditions. Both tensile stress and compressive stress could be created by IAD, and the chemical bonding state of Ti may affect the stress behavior. The network size of the chemical bonds may affect the stress direction.

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.

Analysis of long-term internal stress and film structure of SiO2 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.