Zinc Selenide (ZnSe) Prism Grade
|Bulk Absorption Coefficient @ 10.6µm||≤ 0.0005 cm-1|
|Temperature Change of Refractive Index @ 10.6µm||61 x 10-6/°C|
|Refractive Index Inhomogeneity @ 632.8 nm||< 3 x 10-6|
|Effective Focal Length (EFL) Tolerance||F20-mm ±2%|
|Dimensional Tolerance||Diameter: X mm +0.000”-0.005”
|Edge Thickness Variation (ETV)||<= 0.002”|
|Clear Aperture (polished)||90% of diameter|
|Surface Figure at 0.63µm||Plano: 1 fringe Power
1/2 fringe Irregularity Radius: varies depending upon radius
|AR Coating Reflectivity per Surface at 10.6µm||<= 0.20%|
For proper performance with a plano-convex lens, the curved surface should face toward the incoming collimated beam or the longer conjugate distance (the object and image distances together are referred to as the conjugate distance).
Contaminated optics Contamination due to foreign materials on the optic’s surface includes dust, oil, grease, fingerprints, and hydrocarbons. These contaminants, if deposited on the optic’s surface, may lead to absorption and shorten optic lifespans and efficiency. Localized heating, caused by contamination, can lead to “thermal runaway” in high-power laser optics. High temperatures create an increase in free carriers within the bulk material which increases absorption. This process reaches an avalanche state, and thermal runaway commences at > 50° C for Ge, and > 200° C for ZnSe and GaAs.Surface.