Room-temperature, near IR fluorescence of high optical quality KTP

We have investigated room temperature fluorescence in the 500-900nm spectral region from high optical quality, polished and uncoated KTP crystals from three different commercial vendors. The crystals were all cut into 5mm x 5mm x 5mm cubes with their dielectric axes along the cube edges. The pump source was a tripled Nd:YAG laser operating at 355nm and 7mJ energy having 3ns pulse width and 100Hz pulse repetition rate. Samples from two vendors showed low fluorescence of similar magnitude while samples from the third vendor showed nearly two orders of magnitude higher value in the peak fluorescence near 800nm. In addition, all samples showed a weaker secondary fluorescence band peaking near 600nm. A low fluorescence sample from one of the vendors also showed typical "gray tracking" at these pump radiation conditions. We have also measured lifetimes of 2.9±0.7 µs and 4.9±0.1 µs for the centers responsible for fluorescence near 845nm and 595nm respectively in the KTP sample showing highest fluorescence and "gray tracking" in this group of samples. The manufacturing processes used to produce high optical quality and low fluorescence KTP materials are proprietary to the commercial vendors and were not provided. Possible origin and sources of fluorescence in these materials are discussed consistent with those published in the literature.