Research Of Eliminating The Obscuration Of Laser Beam Expander

With no chromatic aberration,it eliminated the center block of Cassegrain system and improved energy utilization as well so that it is much more suitable for large diameter and high power laser machine.However,the central occlusion phenomenon makes about 40% of the energy loss in the beam expanding process.In order to meet the requirements of high-power lasers launch system for high energy efficiency,we proposed a composite laser beam expander based on reflective Cassegrain beam expander.According to the principles of Cassegrain system,we put forward a composite laser beam expander of 550 mm launch diameter which maintained the advantages of Galileo refraction type beam expander.We combined the reflection type beam expander with refraction type beam expander.Opening a hole in the center of the second mirror of Cassegrain,the central blocked laser can pass through.The Galileo transmission type beam expander was installed behind to expanding the center light,emitting the two light beams in same direction coaxial.We took experiments of laser transmission for verification.And the results showed that the transmittance of 10.6μm laser is up to 95.21%,with an increase of 22.12% than the traditional Cassegrain beam expander.So the composite laser beam expander has fully meet the design goals of high energy efficiency for high power laser emission system.Through the design and experimental verification for the new beam expander,the beam expander can eliminate the central blocking under the condition of maintaining the original characteristics of the Cassegrain system,which provided important reference and guidances for the research and development of the strong laser emission system.