Space based laser missions have gained their popularity in areas such as: communication, power
beaming, ranging, altimetry, and Light Detection and Ranging. The capabilities of 1.0 micron lasers
offer a host of improvements in the knowledge gaps that exist and help promote our understanding
of our Earth and lunar environments as well as planetary and space science applications. Some past
and present National Aeronautics and Space Administration missions that have been developed for
increasing our universal knowledge of such environments and applications include: The Shuttle
Laser Altimeter, Mars Orbiter Laser Altimeter, Geoscience Laser Altimeter System, Mercury Laser
Altimeter, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, and Lunar Orbiter
The effort of contamination control depends on the specific performance goals, instrument designs,
and planned operating scenarios of such missions. Trace amounts of contamination have been
shown to greatly reduce the performance of 1.0 micron space based laser systems. In addition, the
type of contamination plays an important role in the degree of degradation and helps to define the
"contamination sensitivity" of the mission. A space based laser mission is considered highly
contamination sensitive and therefore requires an unprecedented contamination control effort.
A mirror cleaning study was conducted to assess the effectiveness of three cleaning methods in their ability to remove particulate contamination from reflective mirror surfaces. Presently, the detergent bath, solvent rinse, and CO<sub>2</sub> snow cleaning methods are the most commonly used optical cleaning techniques within the optics industry. These techniques are also commonly used by the Optics Branch/Code 551 at Goddard Space Flight Center (GSFC) to remove particulate contamination from optical surfaces. In this experimental study, the above-mentioned cleaning methods were used to clean twelve uncoated silicon wafers, twelve gold coated silicon wafers, and twelve gold coated silicon wafers with a silicon oxide protective coating. CO<sub>2</sub> snow cleaning had an average removal percentage of 84%, followed by the solvent rinse at 74%, and the detergent bath at 61%. In addition to the average removal percentage, this comparative study was designed to: (1) determine the cleaning ability of each method based on the number and size of removed particles;
(2) assess the risk of surface damage for each cleaning procedure;
(3) evaluate each cleaning method as a function of its initial "qualitative" contamination level ("fairly clean", "dirty", and "very dirty").
The particulate cleanliness of all wafers was characterized using Image Analysis and Image-Pro Plus 5.0 software. In addition, the experimental design and experimental results were analyzed using JMP/Statistical Analytical Software Version 6.0.