NATURE OF THE INFRARED-SPECTRUM IN BAND-EDGE REGION OF KTIOPO4

The infrared transmission spectra of KTiOPO4 (KTP) have been closely inspected in the region between 4000 and 1000 cm-1 (2.5-10 mu-m) using single-crystal samples of various thicknesses. The spectral information obtained reveals that the band edge at 4.5-mu-m is due to the first overtone of the upsilon-3 tetrahedral phosphate fundamental vibration. A heretofore questionable absorption centered at 3.3-mu-m has been shown to be the second overtone of this same fundamental vibration.