By using an optical parametric amplifier (OPA), we have measured the non-critical phase-matching (NCPM) wavelengths for frequency-doubling (including type I and type II) in different GdxY1-xCOB crystals. From the Sellmeier equations, of YCOB and GdCOB, we calculated the ranges of NCPM wavelengths in GdxY1-xCOB, and compared them with the data obtained from our experiment. When the output power of a mode-locked Nd/YAG laser is 110 mW (lambda = 1.064 mum), a conversion efficiency of 37 is obtained for the type II NCPM frequency-doubling in Gd0.2Y0.8COB crystal. Using a KTP crystal as frequency-doubler, we have achieved NCPM third harmonic generation (THG) in Gd0.22Y0.78COB crystal. When the output power of Nd/YAG laser is 94 mW and the power of the second-harmonic wave is 38 mW, THG conversion efficiency can reach 21. (C) 2001 Published by Elsevier Science Ltd. References: 8
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