A method for high precision attenuation of the high-power laser beam based on Fresnel reflection

For the high power laser system, the power of laser to the target, the power of the bucket and the beam quality are important parameters, which have important value of identification and evaluation. However, the power density of high power laser are too high to affect the test system. And the high precision attenuation method of Fresnel reflection method can effectively solve this problem. The laser incidents on Front surface of uncoated dielectric material at near normal products different reflectivity of components in s-direction and p-direction. The effect of the difference of reflectivity can be effectively solved by placing a pair of wedge off the axis and changing the polarization state of the reflected light, the reflectivity of the S-direction is as same as p-direction components at every two stages by two normal vertical reflectors. The accurate reflectivity can be obtained according to the refractive index coefficient of dielectric materials. Under the condition of low-power near-infrared power incident light, the calculated results are consistent with the measured results. And under the condition of high power density, we study the thermal deformation of fused silica mirror. A mirror thermodynamics model based on the software was built. And experimental measurements for thermal deformation were performed with laser intensity as high as 44 kW/cm2. The thermal deformation mainly depends on the absorption of the film layer. Therefore, shape variables can be significantly reduced by using a non-coated lens or reducing the absorption of the film.