CW gray-track formation in KTP

Summary form only given. Gray track damage in KTP crystals exposed to high power visible radiation is well known. Recently, two parallel absorbing tracks on opposite sides of the pump beam (double-tracks) were found in KTP crystals subject to high average-power high-repetition-rate green laser radiation. We report on the same effect observed with CW-laser radiation. Photothermal common-path interferometry (PCI), a modification of the photothermal technique with interferometric sensitivity, was used to detect double-track formation in the early stage of its development. Two pump beams were used, IR (1064 nm) and green (532 nm or 514 nm). A crossed-beam configuration with both pump beams collinear and probe beam crossing them inside the sample made it possible to resolve bulk and surface absorption in KTP.