Fabrication and properties of third harmonic beam splitter

Third harmonic beam splitter at 355 nm was deposited on silica substrates by electron beam evaporation and photoelectric maximum control method. Part of the samples were annealed in air at 250 ℃ for 3 hours. The optical transmittance of samples was measured by spectrometer LAMBDA900, the weak absorption of coatings was characterized with surface thermal lensing technique (STL), and the laser induced damage threshold (LIDT) of coatings assessed using 355 nm Q-switch pulsed laser at a pulse length of 7 ns. It was found that the samples had good spectrum performance before and after annealing. After annealing the LIDT of the samples at 1 064 nm increased remarkably from 14.6 J/cm2 to 18.8 J/cm2 with the decreasing of absorption from 1.07×10-4 to 6.2×10-5, but the LIDT at 355 nm decreased o