Study On Measurement Of The M~2 Factor Based On Defocus Gratings

The evaluation of beam quality is paid more and more attention,as the laser is used widely in many fields.Compared with other parameters,the M2 factor has many advantages. Although the M~2 factor can characterize the laser beam quality logically,the conventional measurement has many constraints.Crossed phase defocus gratings,which let us to get the beam spots at 9 various positions of the same beam to be measured simultaneously,are designed and a new technique for real-time measurement of beam quality factor M~2 is achieved in this paper.We first introduce the methods of measuring M~2 and the principle of defocus gratings, and then describe in detail the design of the gratings,the designed parameters of which is validated by using Zemax.A He-Ne laser beam is measured by using the gratings designed and a M~2 value is achieved.Compared with a conventional measurement based on a scanning sensor,the difference is between 3%and 18%.It is validated that the measurement based on defocus gratings is in effect.At last,the origin of the errors is analyzed.The results of this dissertation lay a foundation to form an applied system for real-time measurement of the M~2 factor and will be useful for the applications in future.