Non-critical phase matching of GdxY1−xCa4O(BO3)3(GdxY1−xCOB) crystal

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 (λ=1.064 μm), 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%.