High-reflective films refer to optical films with the function of increasing reflection. It is generally divided into two major categories: metal reflective films and all-dielectric reflective films, or metal dielectric reflective films that combine both.
Metal reflective films take advantage of the fact that common metals have a relatively large extinction coefficient. As a result, the amplitude of light entering the interior of the metal rapidly decays, and the light energy correspondingly decreases while the reflected light energy increases. The advantages of metal reflective films are their simple preparation process and wide operating wavelength range. The disadvantages are high light loss and the fact that their reflectivity cannot be very high.
The reaction enhancement effect of all-dielectric reflective films is based on the multi-beam interference effect.
Dielectric Coating
Dielectric Coating provides high reflectance over a broad bandwidth. Ideal for a tunable laser or in white light applications, used in 250nm~2200nm. It is generally used in single wavelength laser cavity where the lowest cavity loss at a center wavelength is essential.
Metallic High Reflection Coating
Metallic High Reflection Coating is mainly practiced using Au, Ag, Cr, or Ni-Cr. This kind of coating is applied to the situation where a consistent high reflection on a wide spectral range is needed. Their reflectance is lower than that of dielectric HR coating, but their spectrum can cover near-UV, visible and near-IR. Dielectric coating is applied on the layer of metallic coating to prevent metallic coating from oxidization.
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