This paper discusses the results of thermal annealing and in-situ second harmonic generation (SHG) damage tests performed on six rapid growth KDP type 1 doubter crystals at 1064 nm (1 omega) on the Zeus automated damage test facility. Unconditioned (S/1) and conditioned (R/1) damage probability tests were performed before and after thermal annealing, then with and without SHG on six doubter crystals from the NIF-size, rapid growth KDP boule F6. The tests revealed that unannealed, last-grown material from the boule in either prismatic or pyramidal sectors exhibited the highest damage curves. After thermal annealing at 160 degreesC for seven days, the prismatic sector samples increased in performance ranging from 1.6 to 2.4X, while material from the pyramidal sector increased only modestly, ranging from 1.0 to 1.3X. Second harmonic generation decreased the damage fluence by an average of 20 percent for the S/1 tests and 40 percent for R/1 tests. Conversion efficiencies under test conditions were measured to be 20 to 30 percent and compared quite well to predicted behavior, as modeled by LLNL frequency conversion computer codes. The damage probabilities at the 1 omega NIF redline fluence (scaled to 10 ns via t(0.5)) for S/1 tests for the unannealed samples ranged from 20 percent in one sample to 90-100 percent for the other 5 samples. Thermal annealing reduced the damage probabilities to less than 35 percent for 3 of the poor-performing crystals, while two pyramidal samples remained in the 80 to 90 percent range. Second harmonic generation in the annealed crystal increased the S/1 damage probabilities on all the crystals and ranged from 40 to 100 percent. In contrast, R/1 testing of an unannealed crystal resulted in a damage probability at the NIF redline fluence of 16%. Annealing increased the damage performance to the extent that all test sites survived NIF redline fluences without damage. Second harmonic generation in the R/1 test yielded a damage probability of less than 2 percent for the annealed crystal. These results indicate that a combination of thermal and laser conditioning would virtually eliminate bulk damage at the highest NIF fluences and indicate the need for laser conditioning of NIF SHG crystals.
