Diagnosis And Measurement Of Laser Beam Quality

High beam quality,an important factor of the laser facility,shows the significant guidance to the laser design,fabrication,assessment,and application.High quality output is more vital than other common characters,such as high energy/power,especially in the area of far field energy direction and focusing.This work review the quality assessment methods in the current research of laser beam diagnosis,including assessing focusing spot size ?f and far field divergence angle ?,beam quality factor?,Strehl ratio SR,beam propagation factor M2,encircled energy BQ,beam propagation factor BPF,etc.The author then discussed their application,advantages,and disadvantages,and uncovered the fact that the laser beam quality assessment,experiments,and data analysis need united standard.In the thesis,the author firstly introduced classical scalar diffraction theory,Fresnel diffraction approximation,Fraunhofer approximation,and aberration wavefront parameters,and proposed the far field intensity distribution of circle and square uniform plane beam.Both the ideal beam and aberration beam with wavefront phase information were calculated under the condition of far field transition for different shape and size of diffraction aperture.Based on the different aberrations of the far field intensity distribution with wavefront,the article discussed the beam assessment method of the small aberration mode.The author also presented the non-uniform correction algorithm for the focal plane array detector.After reviewing the two kinds of non-uniform correction algorithm,this work proposed the general algorithm for the infrared radiation source and self-adaption case.Then the author analyzed the several sorts of non-uniform correction algorithms,such as two points correction algorithm,multiple points correction algorithm,THPFC,ANNC,etc.The far field infrared images were used to exam those algorithms,and concluded the prospects of the non-uniform correction algorithm in the infrared measurement system.At last,the article introduced the GUI software based on Lab VIEW,which is capable to measure fiber laser output power,near filed intensity distribution,and far field beam quality.The experimental optics and other devices were set to assess the high power fiber laser output quality.The results were then compared with those from commercial measurement system,and achieved the consistence.