| 摘要 |
PURPOSE:To detect a minute pinhole with high sensitivity, by dividing the surface of a mirror into a vicinal region containing a point crossing an optical axis and the other region and making the reflectivity of the vicinal region lower than that of the other region. CONSTITUTION:Laser beam 5 is converged to an object 4 to be inspected to scan the same. Transmitted beam 6 in a narrow sense forms a small beam diameter as shown by a dotted line and forward scattering beam 7 is relatively widely diffused as shown by a broken line. A mirror 8 is provided so as to bend transmitted beam 6 and scattering light 7 at almost right angles and reflected beam is converged by a lens 9 to be detected by a beam receiving element 10. The surface of mirror 8 is divided into a vicinal region 8a containing a point crossing an optical axis and other regions 8b, 8c. Then, the reflectivity of the region 8a is set to about 1/8 as compared with the other regions 8b, 8c. By this method, a minute pinhole can be also detected with high sensitivity and a signal is not saturated even by a large pinhole. |
