Optical cavity surface coatings for 1 micron laser missions

The particulate surface cleanliness level on several coatings for aluminum and beryllium substrates were examined for use in the optical cavities of high pulse energy Nd:YAG Q-switched, diode-pumped lasers for space flight applications. Because of the high intensity of the lasers, any contaminants in the laser beam path could damage optical components and limit the instrument mission objectives at the operating wavelength of 1 micron (μm). Our goal was to achieve a Mil-Std 1246 level 100 particulate distribution or better to ensure that particulate redistribution during launch would not adversely affect the mission performance objectives. Tapelifts were performed to quantify the amount of particles using in-house developed procedures. The primary coatings included chromate conversion coated aluminum (Al), uncoated (bare) Al, electroless nickel (EN) on Al, gold (Au)/EN on Al, anodized Al, and Au/EN on Beryllium (Be). When considering applications that need to meet launch environments, the results indicate advantages in Au/EN coating applications for the two major substrates, Al and Be.