Page 432 - High Power Laser Handbook

400 So l i d - S t at e La s e r s The National Ignition Facility Laser 401

300

90% Encircled power diameter (µm) 200

100

Flat-in-time pulses
540 TW shaped pulse

0
0 100 200 300 400 500 600
3ω power (TW FNE)
Figure 14.38 Unconditioned (no beam smoothing applied) far-field spot size
as a function of peak beam power, measured on PDS. No significant spot
size increase is observed for beam powers up to about 10 percent above the
maximum design power. The spot size is comfortably less than the design
requirement of 80 percent of the pulse energy within a 600-μm diameter.

A viable inertial fusion campaign has a number of stringent
requirements, laid out both in the 1994 primary criteria and in the
succeeding capsule, hohlraum, target positioning, and laser-
performance specification roll-ups that have come to be known as
Rev. 1 through Rev. 5 point designs. Beyond global numbers like
energy, peak power, and temporal-pulse contrast, these point designs
specify details such as time-dependent power balance, pointing accu-
racy, beam synchronization, shot-to-shot pulse reproducibility, and
finesse in making small adjustments to the pulse shape to accommo-
date the results of pulse-tuning experiments. Figures 14.39 to 14.43
address the current state of NIF’s demonstrated ability to achieve
these requirements.
Power balance and pulse-shape reproducibility are illustrated in
Figs. 14.39 and 14.40. Figure 14.39 is single-beam PDS data. A sequence
of 16 shots was fired, holding constant the nanojoule pulse shape
requested from the MOR. The desired 1.3 MJ Rev. 2 3ω pulse shape is
shown, along with the time-dependent power balance specification
and the time-dependent rms variation actually achieved among the
16 shots. Treating the variation among multiple shots of a single
beamline as a surrogate for the variation among multiple beamlines