| 摘要 |
A device for scanning a surface is described, which device comprises a radiation source (5), a transparent plate (18) provided with a grating (17) having two grating structures, an objective system (7) for focusing the radiation on a surface (3), and a detection system (12) for converting radiation reflected by the surface into electric signals. The first grating structure in the grating (17) is intended, for example for forming two side beams (21, 22) from the radiation beam (6). By providing the second grating structure, a monitor beam (13) is obtained in reflection from the radiation beam (6). The monitor beam is directed onto a monitor detector (14) which generates an electric signal with which the radiation power of the radiation source (5) is controlled. <IMAGE> |
