Optical design of a hybrid approach to focus control of an imaging system

Laser systems often require the placement of the beam waist far from the primary mirror of a beam director system. It is often the case that a range of foci are required to meet requirements. The focus of this paper is to examine the methodology of designing the system with dynamic focus control. This is achieved through the use of a fixed focal length telescope with a deformable mirror being driven by either a feed forward or a closed loop algorithm to push and pull the focus of the system. This is defined as the hybrid approach. The system is approximately diffraction limited for all required foci. A trade study was conducted to select the hybrid approach to focus control, the modeling and analysis for which was done in Ansys Zemax. This trade study is used to select the hybrid approach and compare it to other approaches. The traditional translating secondary approach for dynamic focus control is also discussed in this paper.