摘要：

According to the invention, a doubly focused optical system having an ellipsoid of rotation is provided, one focal point (P1) of which is situated on the surface of the testpiece (2), in particular a glass substrate, and the other focal point (P2) of which is situated on the surface of a detector (6). The system is provided as a reflector (4) for the scattered radiation of the light beam (10), whose angle ( alpha ) of incidence is at most 25 DEG . This arrangement can be used to detect in a simple way dust particles adhering to the surface and having an extent of substantially less than 1 mu m.

展开