Long-lifetime, low-contamination metal beam dumps for NIF spatial filters Page: 4 of 13
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To pass 3 reflections
Pockels beam dump
:............. ...... ........ Output
To pass 5 filter
Pass 4 beam dump
Figure 1. Schematic of the NIF laser architecture.
injected near the pinhole plane of the transport spatial filter (TSF). It then passes through
the booster amplifiers into the 4-pass cavity by reflection from a polarizer. The Pockels
cell is activated to keep the beam in the cavity for four passes through the cavity amplifiers
before it is deactivated to return the main beam to the booster amplifiers. The combined
performance specifications of the polarizer and Pockels cell allow 0.01% leakage into the
cavity after the fourth pass. The path of the residual beam in the cavity, which makes a
fifth pass after the main beam is sent out, is shown in Figure 1, where it is drawn below
the path of the main beam. Since each pass is separated from the adjacent pass by a small
angle, on the order of 1 mrad, the residual beam is directed toward a new location in the
cavity spatial filter pinhole plane, and it has its own pinhole. The required beam dump will
be located just beyond this pinhole.
The portion of the main beam which is back-reflected at the target, along with that
which is back-reflected from the output pinhole of the TSF, can return along the outgoing
path in the outgoing polarization state. After completing a round trip through the booster
amplifiers and the cavity amplifiers, such a beam will arrive at a displaced position in the
pinhole plane of the TSF. We designate this location as the pass 3 pinhole. This path is
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Boley, C D; Murray, J E; Neeb, K; Norton, M A & Sinz, K. Long-lifetime, low-contamination metal beam dumps for NIF spatial filters, article, October 30, 1998; California. (digital.library.unt.edu/ark:/67531/metadc626858/m1/4/: accessed May 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.