| 摘要 |
PROBLEM TO BE SOLVED: To narrow the line band as desired without substantially reducing the laser efficiency, by comprising at least a specified number of prisms, positioning each prism at an incident angle in a specified range, and applying a single layer coating of a strong material having a high refractive index to the oblique side of each prism. SOLUTION: A beam expander is composed of at least four prisms 26, 28, 30, 32 made of CaF2. By increasing the number of prisms, required magnification for each prism 26, 28, 30, 32 can be lowered and hence the incident angle on the oblique side of each prism 26, 28, 30, 32 can be reduced to 67-71 deg., e.g. 68.2 deg., this enabling the use of a high refractive index material of a single layer such as nonreflective coating. Thus, a high efficiency can be attained and a good line band-narrowing can be attained, without using a high-cost, easily breakable multilayer nonreflective coating of a high incident angle. |
