Widely Tunable Angular Non-Critical Phase-Matching Wavelengths from 0.72 to 1.42 μm Based on RE1xRE21-xCOB Mixed Crystals

The angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) properties of RE1(x)RE2(1-x)COB (RE1, RE2 = Y, Gd, La, Tm, Sm, and Nd) type mixed crystals including NCPM wavelength and conversion efficiency were detailedly investigated. Theoretical calculations manifest that the A-NCPM SHG scope of these crystals is 0.72 similar to 1.42 mu m, and in experiments, the A-NCPM SHG waveband of 0.72 similar to 1.25 mu m has been realized, by changing the ratio of the rare-earth elements RE1 and RE2 in RE1(x)RE2(1-x)COB crystals. Comparing to the temperature-dependent A-NCPM SHG of 0.95 similar to 1.34 mu m in LiB3O5(LBO) crystal, the composition-dependent A-NCPM SHG of 0.72 similar to 0.95 mu m in RE1(x)RE2(1-x)COB type crystals is unique and has special significance for the frequency conversion of Ti:Sapphire lasers. Relationships between the birefringence and radius of rare-earth ion RE(3+)in RE1(x)RE2(1-x)COB mixed crystals were discussed. Aiming for the A-NCPM SHG of 0.72 similar to 1.42 mu m, we supply a clear, completed, and optimized solution on how to select the compositions of RE1(x)RE2(1-x)COB mixed crystals. Under focusing light beam conditions, high efficient A-NCPM SHG for both OPO and Ti:sapphire lasers were realized experimentally by using long Y- and Z-cut RE1(x)RE2(1-x)COB crystal samples.