We describe the cleaning processes, treatment methods, facilities, and cleanliness verification techniques developed to
achieve and maintain the demanding cleanliness requirements for both hardware and optics used in the National
Ignition Facility (NIF).
High power laser systems require nearly contamination free optics to maintain desired transport efficiency and to
minimize optic damage. The required cleanliness is generally achieved through practices that preclude or remove
foreign particle contamination. However, laser optic systems may also be contaminated by vapor-borne contaminants
from material outgassing, by particles ablated from surfaces exposed to amplifier or laser light, or by contact with items
used in the production and cleaning of optics and components. To minimize such contamination on the optics of the
National Ignition Facility (NIF), a rigorous screening test program was introduced. This test program replicates
conditions in the beam path as well as conditions during production and cleaning. The former is represented by sol-gel
exposure tests and by subjecting materials to amplifier flashlamp light and 1ω laser light. The latter is represented by
organic solvent extraction tests and surface contact tests for items that could contact optic surfaces. This paper will
discuss the methodology for, and administration of, these tests and present results for selected materials.
A key lesson learned from the earliest optics installed in the National Ignition Facility (NIF) was that the traditional approach for maintaining cleanliness, such as the use of cleanrooms and associated garments and protocols, is inadequate. Assembly activities often negate the benefits provided by cleanrooms, and in fact generate contamination with high damage potential. As a result, NIF introduced "clean assembly protocols" and related practices to supplement the traditional clean room protocols. These new protocols included "clean-as-you-go" activities and regular bright light inspections. Introduction of these new protocols has greatly reduced the particle contamination found on more recently installed optics. In this paper we will describe the contamination mechanisms we have observed and the details of the clean assembly protocols we have successfully introduced to mitigate them.
We describe a system to inspect and remove surface debris in-situ from the surfaces of upward-facing mirrors that transport 1053 nm laser light to the target chamber of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory. Grazing angle (2-5°) illumination with a bar light highlights debris ≈10 mm in size and larger, which is then viewed through windows in the enclosures of selected mirrors. Debris is removed with 1-second bursts of high velocity (76 m/s) clean air delivered across the optic surfaces by a commercially available linear nozzle ("gas knife"). Experiments with aluminum, stainless steel, glass and polystyrene particles of various sizes >30 mm show that particle removal efficiency is near 100% over most of the mirror surfaces for all sizes tested.