Enhanced Internal Reflection Microscopy for Subsurface Damage Inspection

A new method is proposed to inspect the subsurface damage (SSD) that plays a key role on improving the laser induced damage threshold (LIDT) of optics applied in high power laser system. This method is based on total internal reflection microscopy (TIRM) and digital image processing technique. Because of relatively small depth of focus of a microscope at large magnification, a series of TIRM images can be obtained while the microscope focuses into different depths of sample by micro-focusing control. Definition of each image is calculated through wavelet transform. The relation between definition of TIRM images and the depth of SSD is established. According to the definition curve, the position and size along the depth direction can be acquired simultaneously. The measurement accuracy is dependent on the depth of field of microscope. This proposed method has been applied to measure the SSD information of finished K9 glass, fused silica glass and Nd-doped glass.