LINE NARROWING APPARATUS WITH HIGH TRANSPARENCY PRISM BEAM EXPANDER

摘要

A grating based line-narrowing apparatus having a prism beam expander with at least four prisms (26, 28, 30, 32). Each prism is positioned at an incidence angle between 67 and 71 degrees. A single layer coating of high refractive index, robust material, such as A1/2O/3, is applied to the hypotenuse face of each prism, providing an efficient, antireflection coating. In a preferred embodiment the incident angle of the four prisms (26, 28, 30, 32) are each at about 68.2 degrees. The laser (21) of the preferred embodiment has similar line narrowing efficiency and bandwith as that for a laser (21) with a 3 prism, ideal multi-layer anti-reflection coated beam expander. The primary benefit of the new four prism (26, 28, 30, 32) arrangement is that the prism coatings should be much less expensive and have greatly increased durability. Applicants have tested the new prisms for 30 million, 10mJ pulses in air with no noticeable degradation. No present day dielectic multi-layer stack coating could survive such exposure.