Abstract
Noncritical Type I birefringent phase matching for infrared-to-visible nonlinear frequency conversion in the blue-green region of the spectrum, requires heating LiNbO3 congruent crystals very frequently to temperatures in excess of 100 °C. We have obtained accurate control of the room temperature fundamental wavelength in noncritical Type I second harmonic generation (SHG) in LiNbO3 crystals by adding a controlled concentration of K2O to the congruent melt in a Czochralski LiNbO3 crystal growth process. A variable concentration of K2O (0 - 9 wt. %) controls the final Li/Nb ratio in the crystal1 between congruent and stoichiometric compositions, and thus the amount of birefrigency2. We have experimentally obtained room temperature noncritical Type I phase matched second harmonic generated for fundamental wavelengths extending from 1074 nm (congruent, green SHG) to 972 nm (stoichiometric, blue SHG) in a set of LiNbO3 crystals grown with different K2O concentrations. The linear variation of fundamental wavelength with K2O concentration permits accurate tuning of the noncritical fundamental wavelength for SHG. This principle is extensible to other noncritical frequency conversion processes.
© 2000 IEEE
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