Laser damage threshold of optical components is an important indicator to measure the ability of components to resist laser damage. A low-absorption film is plated on the surface of the reaction sintered SiC substrate produced by ion beam sputtering method, and the fundamental frequency reflection efficiency is over 99.8%. A set of 1060 nm continuous laser damage threshold testing system has been established. After loading the SiC-based film sample with a continuous wave laser with a power density of 30 kW/cm2 for 30 s, it was found that the surface temperature rise of the SiC-based film was less than 2 K. the changes of temperature field and thermal stress on the surface of the SiC mirror when the continuous laser loading power and loading time by finite element method. The results are basically consistent with the experimental data. The experimental results verify that the thermal stress and thermal melting effect caused by high-power continuous laser loading are the mechanisms for the damage of mirrors, which provides an idea for improving the laser damage threshold of optical components.
Ta2O5/SiO2 mixed film is a very promising material for the preparation of new optical and optoelectronic devices, but there are few reports on its etching characteristics. In this paper, Ta2O5/SiO2 mixed films with various proportions of Ta2O5 were prepared by ion-beam sputtering deposition. CHF3-based reactive ion etching (RIE) was used to etch Ta2O5/SiO2 mixed films. The etching profiles of Ta2O5/SiO2 mixed films were observed by using a field-emission scanning electron microscope (SEM). The RIE etch rates were investigated as a function of the Ta2O5/SiO2 mixture ratio, RIE power, chamber pressure and etching gas ratio. It is found that the etch rate of Ta2O5/SiO2 mixed films increase with an increase of RIE power and chamber pressure, and decrease with an increase of Ta2O5 composition in the Ta2O5/SiO2 mixed films. Moreover, it is also found that as the proportion of F-based gas increases, the etching rate of the Ta2O5/SiO2 mixed film first increases and then saturates. These results would be of importance for the fabrication of optical and optoelectronic devices based on Ta2O5/SiO2 mixed films.
High repetition rate picosecond laser induced damage properties of Ta2O5/SiO2 dielectric reflective optical coatings were investigated. The laser induced damage was attributed to the increase of the free electron density and temperature enhancement during the irradiation of high repetition rate picosecond laser. The correlation of laser induced damage threshold with pulse numbers was researched. At higher repetition rate, the laser induced damage threshold was reduced more with the increasing of pulsed number. We found that the defects absorption played an important role to the laser induced damage properties of dielectric reflective optical coatings. The damage morphology showed that the evolution of damage site was significantly influenced by the accumulation of laser energy. In order to enhance the resistance capacity, the dielectric reflective optical coatings were annealed with temperature of 260°C. The defect absorption was reduced after the annealing process. For the annealed coating, the laser induced damage threshold under high repetition rate picosecond laser was enhanced as a result of the suppression of defects in the coating.
In this paper, we designed the broadband all-dielectric reflection phase shifting mirror to convert the linear polarization incident light to circularly polarization reflected light in the design wavelength range (750nm~850nm) for ultra-high intensity laser application. The 48 multilayer coated mirror used Ta2O5 and SiO2 as high and low refractive index materials. The theoretical design results indicated that at the incident angle 45 degree, the reflectivity of s- polarization light exceeded 99.9% and p- polarization light exceeded 99.5%, and phase shift values between s- and p- polarization lights were -90±5 degrees in the design wavelength range. The all-dielectric broadband reflection phase shifting mirror was fabricated with an ion beam sputtering system. The measurement results indicated that the reflectivity of s-polarization light exceeded 99.9% and p- polarization light exceeded 99.3%, and phase shift values between s- and p-polarization lights were -95~-77 degrees. The reflectivity of s- polarization light and p- polarization light conform well to theoretical design values. However, the phase shift values slightly deviated from theoretical design results in part of the wavelength range. With features of high reflectivity and invertible linear to circular polarization conversion, the all-dielectric broadband reflection phase shifting mirror can be a good replacement for quarter wave plate in high intensity laser region, and offers a further step in developing polarization and phase manipulation devices.
Polishing pad becomes aging after finishing for a while, by reason of friction and wear, or polishing particles deposition, which will reduce polishing effects, increase polishing effects and make a low polishing quality. When the ultra-hardness of sapphire material needs high pressure and high rotate speed parameters, which will accelerate aging of polishing pad. When large scale sapphire optical window is finished by computer controlled optical surfacing (CCOS) method, the polishing pad aging problem is an important confinement factor for high quality of polishing. In this paper, we confirmed the stable polishing period and aging time node of pitch pad and polyurethane pad by polishing experiments. For pitch pad, time aging nodes are between 50min and 75min with polishing pressure 0.1Mpa and 0.2Mpa and between 25min and 50min with polishing pressure 0.4Mpa. For polyurethane pad, the time aging nodes are over 75min with polishing pressure 0.1Mpa and 0.2Mpa and between 50min and 75min with polishing pressure 0.4Mpa. The aging time of polyurethane pad is later than that of pitch pad. Increasing polishing pressure will help increase material removal rate, but will accelerate aging of polishing pad
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