V-Coatings
V-coatings are multilayer antireflection coatings that reduce the reflectance of a component to near-zero for one very specific wavelength. Our V-coatings are intended for use at normal incidence, for maximum reflectances of not more than 0.25% at their design wavelength. V-coatings are extremely sensitive to both wavelength and angle of incidence. For example, a V-coating intended for the helium neon wavelength (632.8 nm) when used at 30-degree incidence will reflect about 0.8%. At 45-degree incidence, the same coating will reflect over 2.5%. If your application involves other than normal angles of incidence or high-numerical-aperture (low f-number) optics, it may be better to use a HEBBAR™ coating. Experience shows that the maximum reflectance typically achieved by these coatings is often closer to 0.1% than the 0.25% we specify. Using V-coatings on fused-silica optics can therefore provide exceptionally high external transmittances. The reflectance curve for a typical V-coating, on BK7 glass, designed for operation at 632.8 nm is shown below. |
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Example of a V-coating for 632.8 nm |
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Clearly the performance of such a coating is highly dependent on the
refractive index of the component material. However, we specify all
coatings by performance figures and not by design. This means that we
will change the design to suit the material being coated. This makes
ordering coatings simple: select the specification you want to achieve,
tell us what to put it on, and we do the rest. This means that your
reflectance curve may vary from the one shown on this page, but the
coating will meet your requirements. In addition to the standard coatings
listed here, Melles Griot can supply V-coatings at any center wavelength
from 193 nm to 2000 nm. These coatings are not intended for use with high-energy lasers although the Nd:YAG coatings are suitable for many medium-power applications including diagnostics. |
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| Optics Guide Copyright 2002 Melles Griot Inc. |