2.A Development of Optical Coatings for the OMEGA Upgrade

An intensive in-house effort in the past year has produced coatings and devices that will survive the peak 35 1-nm fluence expected in the OMEGA Upgrade. The stringent ultraviolet requirements for the upgrade stem from the decision to place the frequency-conversion crystals in the laser bay (rather than at the target chamber).l At that time, only one report of satisfactory laser-damage thresholds for 351-nm high reflectors existed.2 Reports of satisfactory distributed phase plates (DPP's) did not exist, and tests indicated the thresholds of existing designs would not suffice. Modification of the laser beam-transport-system design (see Section 1 .A, this issue) lowered the thresholds from those listed in the Preliminary Design Document.1 These new thresholds are listed in Table 44.111. As seen in the table, fluences in the blue were lowered for high reflectors and DPP's, but remained the same for antireflection coatings.