Improving beam profile of LD-Pumped self-frequency-doubled NYAB laser

摘要

Abstract: By means of studding on the characteristics of phase mismatch of Neodymium yttrium aluminum borate $LB@Nd$-x$/Y$- 1$MIN@x$/Al(BO$-3$/)$-4$/; NYAB$RB crystal, a method of improving beam profile of NYAB laser was presented. Because of the exist of little, periodically local shortcomings of NYAB crystal, there were different wave-vector mismatch $Delta@Ks at the different locations of NYAB when a wide incident beam passed through it for SHG. According to the phase matching theory of second harmonic generation, there were different conversion efficiencies at the different locations of the incident beam, resulting in inhomogeneous beam profile of second harmonics. We measured the curves of the SHG efficiencies versus phase mismatch angles of NYAB crystals under cases of different diameters (100 $mu@m - 2 mm) of fundamental wave beam. The curves showed that the phase mismatch acceptance angle $Delta$Theta$-m$/ was very small for the thin incident beam when a very homogeneous harmonic beam was obtained, while $Delta$Theta$-m$/ was large for a wide incident beam and the profile of the harmonic beam was not homogeneous.!2