Yaoning Zhang

Laser-induced temperature distributions and thermal deformations in sapphire, silicon, and calcium fluoride substrates at 1.315 μm

Some expressions for temperature distributions and thermal deformations of silicon, sapphire, and calcium fluoride window substrates at 1.315 μm are derived in terms of Greens function methods. Profiles for temperature rise and thermal deformation as functions of laser power, irradiating time and cylindrical coordinates are given. The calculated results show that under conditions of irradiating by a 10-kW intense laser with Gaussian shape, maximum temperature rises in Al 2 O 3 , CaF 2 , and Si substrates are 5.6°C, 6.0°C, and 35°C, respectively. The amounts of thermal distortion in Al 2 O 3 , CaF 2 , and Si substrates is 0.28, 0.99, and 0.40 μm, respectively. At the initial stage of substrate laser irradiation, the temperature rises and thermal deformation increases quickly. After about 2 s, the increments of the temperature and thermal deformation become small. The trend of thermal deformation versus the heating time is in relative agreement with our experiment.

Experimental research of gasdynamic-cooled discharge CO2 laser

This paper has reported the configuration and output characteristics of gasdynamic cooled discharge CO2 laser. In the same condition, the pre-mixed gasdynamic cooled discharge lasers electro-optic transfer efficiency is up to 11.15%, and there are no obvious difference in its output power and electro-optic transfer efficiency compared with the all-closed laser which needs helium or argon. The designed a downstream-mixed laser can obtain injecting power rate which is greater than 1300 W/gsec-1 and 1% cm-1 small signal gain coefficient. When the total injecting power is 1.8 KW, the power of the output near basic mode laser is 108 W.

Determination of wavefront distortion of an aerodynamic window in a high-power laser

The optical characteristics of new type jet injecting aerodynamic window have studied experimentally with HARTMANN diagnostic apparatus. When the pressure of sealed vacuum chamber is changed from 2500 Pa to 771.4 Pa, the Strehl ratio is determined from 0.94 to 0.90. From these optical characteristics it can be analyzed, that the injection flow pressure and the structure of aerodynamic window influences the passed beam quality on. It was shown that the passed beam well be divergence, as the injection flow pressure becomes large. It is related to the radius gradient of air density distribution, caused by gas flow from circular nozzle. And heterogeneous distribution of air bleed hole makes the wavefront tilt so that the passed laser beam well shift.

Interference measurements for roughness of silicon mirror with Twyman interferometer

Supposed the random distribution of height deviation can be represented as Gaussian distribution, the relationship between intensity contrast C of interference fringes, determined at Twyman Interferometer, and the roughness (sigma) of mirrors surface is deduced. Roughness measurements of four silicon mirrors have performed with Twyman Interferometer. The result of measurements is agree with the data, measured by 6JA profiler in tendency. This method is a full-field, noncontacting interference measurement so that it can be developed as an inspection on line. Then, the surface profile analysis can also be performed from interference fringes. Therefore this method provide a controlling way in polish process.

Flexible focus variable expander

A flexible focus variable beam expander system with adaptive optics is designed. In this system the adaptive mirrors focus is adjusted by regulating the pressure of mirrors cooling water. The change of mirrors curvature and focus is calculated with elasticity mechanics and the conception of wavefront aberration is cited to study the difference between ideal curvature and realistic one. The results of experiments is corresponding to the theoretical data.

Experimental study on microdeformation of water-cooled copper mirrors in high-power laser system

The surface micro-deformations of a cavity copper mirror, an annular channel copper mirror, a multi-layer copper mirror and a sandwich copper mirror are tested when the mirrors are irradiated by high power laser and cooled by water. The test result shows that the surface deformation values of the multi-layer copper mirror and the sandwich copper mirror are much smaller than the cavity copper mirror and the annular channel copper mirror, and the multi-layer and the sandwich copper mirror can meet the requirement of a high power laser system on very small mirror surface deformation.

Superthin multilayer mirror

The rule of the distortion introduced by pressure and thermal stresses in the active cooling mirror were proved experimentally. In order to minimize the distortion of a mirror the active cooing mirror should be consisted of a thin faceplate layer, a good heat exchanger layer and a hard rigidity substrate. According to this requirement of a superthin multilayer mirror were designed. Its maximum distortion was only 0.10 micrometers , when the 8.69kw laser beam was incident on the surface of mirror and the coolant pressure was 0.13MPa.