Surface damage growth mitigation on KDP/DKDP optics using single-crystal diamond micro-machining ball end mill contouring

A process to stabilize laser-initiated surface damage on KDP/DKDP optics by micromachine contouring using a single-crystal diamond ball nose end mill is shown to mitigate damage growth for subsequent laser shots. Our tests show that machined circular contours on output surfaces of uncoated doubler (KDP) and tripler (DKDP) crystals are stable for laser exposures at 351nm, ~8ns pulses at ~12J/cm 2 fluences. Other tests also confirmed that the machined contours on the output surface of an uncoated tripler are stable for combined 1053nm and 351nm, ~8ns pulses at ~12J/cm 2 total fluences (~6J/cm 2 each wavelength) for greater than 100 shots. Laser damage tests have also been conducted on an array of machined contours on the output surface of an AR coated tripler at 351nm, ~1ns pulses up to ~8J/cm 2 fluences. The machined shapes have been as large as 1.5 mm in diameter and 0.25 mm deep, and as small as 250 microns in diameter and 25 microns deep. Both Gaussian and conical shaped contours have been successfully tested. Computer modeling and measurement of laser beam propagation through the actual contoured shapes have been conducted to confirm downstream intensification is manageable.