The Role of Pad Block’s Support Surface Topography in the Measurement of Optical Glass BK7’s Surface Figure

Large flat transmission mirrors made from optical glass BK7 are widely used in the high-power laser facility, which are required of stringent specifications for the whole spatial frequency errors. This work reveals the role of pad block’s support surface (PBSS) topography in measuring BK7 surface figure. Firstly, the PBSS topography was measured with laser displacement sensor. Secondly, the BK7 surface deformation at different pad blocks were simulated with finite element method and validated by experiments. Finally, a method was proposed to quantitively evaluate the different PBSS topography.