Unconverted Light
The conversion of the 1ω (1.05-μm) light at NIF into 2ω and 3ω (0.53- and 0.35-μm) light is described in Section 4.5. The effect on the laser system and Target Chamber of the residual 1ω and 2ω light following frequency conversion must be considered in experiment design. The 1ω footprint is approximately 22 mm square with a minimum 4.8 mm clearance from the 3ω focus. The 2ω footprint is approximately 12 mm square with a minimum 2.9 mm clearance.
The overlap of unconverted light from all beamlines has a clear region down the axis of the Target Chamber. An ignition-scale hohlraum fits nearly within this clear region. The envelope of unconverted light extends out to a radius of about 32 mm from TCC, potentially affecting target or backlighter structures or diagnostics.
The majority of this unconverted light propagates past the target and strikes the inner wall panels of the Target Chamber. The footprints of unconverted light at the opposite wall impose a limit on pointing for each beamline in order not to damage near-opposite FOAs by propagating high-intensity unconverted light into the FOA hardware or optics. The unconverted light that propagates past the target strikes beam-dumps consisting of stainless steel louvered panels that are designed to capture this light and prevent any ablated material from being ejected into the chamber.
Unconverted light incident on the target needs to be taken into account and managed with the target design.
