Long-term, independent experiments show a high degradation rate and short lifetime for electroless silver as a mirror coating operating at visible wavelengths in an observatory environment. Acid formed by water vapor mixing with sulfur in volcanic dust diffuses through pinholes in the coating generated during deposition. This causes internal corrosion and delamination after only 3-4 months. In addition, a layer of silver sulfide results in tarnish, which reduces reflectance. Rates of sulfidation and internal corrosion are shown to depend on the concentration of sulfur and the exposure rate. Comparisons of performance, lifetime, and the application process are made with bare aluminum and two variations of enhanced silver.
Most ground-based telescope mirror coatings are exposed to hostile environments, as the humidity, dust, and reactive gases in the air corrode and tarnish the coating. As the coating degrades the scatter increases. Eventually, every mirror needs to be recoated. This is a costly, time-consuming process that requires telescope down time and involves risks to both people and to equipment. The AEOS (Advanced Electro-Optical System) telescope has a mirror purge system that fills the mirror cell with dry air while the telescope is stowed. We present results conclusively demonstrating that this system extends the lifetime of the AEOS primary mirror coating, reducing the need for burdensome recoating.
An AlGaAs diode laser at 760 nm is frequency stabilized to a molecular-oxygen absorption line and is used to injection lock a Q-switched alexandrite laser, which will be used as a lidar source in the remote sensing of atmospheric pressure and temperature. The diode laser operates nominally at 761 nm. Temperature tuning to the absorption feature of interest is accomplished by externally adjusting a temperature-bias voltage to the diode controller. Active frequency stabilization is achieved through photoacoustic feedback by frequency dithering the diode through an oxygen cell. Stabilization to less than 15 MHz has been reported. Successful injection locking of the broadband standingwave alexandrite laser has resulted in a linewidth of less than 500 MHz in an 85 ns pulse, 20 mJ/pulse, 5 pps.
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