THIN LENS EQUATION FOR A REAL LASER BEAM WITH WEAK LENS APERTURE TRUNCATION

The effects of a thin lens on a real laser beam with an M 2 factor larger than 1 is theoretically studied. The effect of weak lens ap- erture truncation is considered by introducing an increment to the M 2 factor. A new thin lens equation is derived. This equation is a simple and effective tool applicable to real laser beams, and can be used to estimate the phenomena of focal shift and change in focused spot size caused by weak lens aperture truncation. Two examples of applications are de- scribed. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)01911-4) have an M 2 factor in the range 13 of 1.1 to 1.7. In both cases, the M 2 factor increased when the truncation intensity level was increased. The M 2 factor varies among different lasers and significantly affects the characteristics of a laser beam. Therefore the M 2 factor cannot be easily neglected in optical design involving laser beams. In this paper, we expand the work of Ref. 9 by deriving a new thin lens equation applicable to a real laser beam, including both the M 2 factor and the effects of weak lens