Metallic High Reflection (HR) Coatings are optical thin films made of metal materials deposited on substrates to provide high reflectance. Metallic HR coatings are often applied to optical mirrors and laser mirrors, but can also be applied to other optical components where maximized reflectivities for a spectral band are required. Common materials used to fabricate metallic coating include aluminum (Al), silver (Ag), gold (Au), etc. The metal coatings can also be combined with a dielectric overcoat to form enhanced or protected metallic coatings.
Metal optical coatings reflect light primarily due to the free electrons in the metal that interact with the electromagnetic waves of the incident light. These free electrons oscillate in response to the incident light's electric field, causing the light to be reflected back. The high densities of free electrons in metal coatings allow them to reflect light with minimal absorption. Compared with dielectric high reflective coatings consisting of multiple layers of dielectric thin films purposed to provide optimized reflective attributes, the most distinguished advantages of metallic coatings are their excellent broadband performance, low wavelength dependence, and slight sensitivity to AOIs. However, metal optical coatings exhibit lower reflectivities than dielectric HR coatings. Therefore, metallic mirror coatings are used when high reflection across a wider wavelength range is needed, and when moderate reflectivities are acceptable.
Metallic mirror coatings can be deposited either on the front surface of the mirror substrate on which the light incident, or on the other surface. When metal reflective coatings are coated on the side of the incoming light, the mirror is defined as a first surface mirror. When metal reflection coatings are deposited on the opposite side, the mirror is referred to as a second surface mirror. For the first surface mirrors, light is directly reflected by the metallic mirror coatings without traveling in the mirror substrates. This is beneficial in the aspect of avoiding the adverse effects and uncertainties from light propagation in the mirror substrates, such as undesired chromatic dispersion from the mirror substrates, wavefront distortion due to optical inhomogeneities of the substrates, and ghost reflections. However, as the second surface mirrors have metallic mirror coatings on the rear side, the metallic coatings are in less danger of oxidation and abrasion injuries.
Enhanced and protected metallic coatings are metal coatings added with single or multiple dielectric layers in order to increase the reflectance and to make the delicate metal mirror coatings more durable and easier to handle.
Hangzhou Shalom EO offers professional custom coating services for metallic high-reflection coatings. Our standard coating material options include silver (ag), gold (au), and aluminum (al). The metallic optical coatings are accessible in bare, protected, and enhanced versions. Metallic mirror coatings with various spectral functions are available, including Broadband HR (BBHR) Metallic Coatings, Narrowband HR (NBHR) Metallic Coatings, Laser Line HR Coatings, Single/Dual/Multiple Wavelength HR Coatings, and Non-polarizing Dichroic Coatings.
For applications requiring very high reflectivities to maintain high power and efficiencies, such as in laser cavities, and beam steering, the metallic coatings are available as enhanced metallic coatings (enhanced silver coating, enhanced gold coating, enhanced Al coating) with a dielectric overcoat to enhance the reflectivities by reducing energy loss. The dielectric overcoat can be tuned to enhance reflectivities for specific wavelength ranges and angles of incidence. To improve the oxidation, abrasion, and tarnishing resistance of metallic coatings, and to prevent permanent damage from intense exposure to laser light, we provide protected metallic coatings (protected Ag coating, protected Au coating, protected Al coating). Shalom EO supplies metallic HR coating service for both first-surface mirrors and second-surface mirrors according to your mirror design.
Below are some examples of the standard types of metallic mirror we offer, where more custom types and bare metallic mirror coatings are also available:
Enhanced Aluminum (Al) Mirror Coating:
Enhanced aluminum HR coating is constructed by Al coatings with muti-layers of dielectric overcoat. The overcoat helps to improve the reflectivities of the aluminum coating while also making the coating more durable. We can provide enhanced Al coatings with reflectance boosted for a specified wavelength range, such as UV-enhanced aluminum HR coatings, the coatings are a cost-effective option for UV applications.
Protected/Ultrafast-enhanced Silver (Ag) Mirror Coating:
To protect the vulnerable silver mirror coating from deliquescence, oxidation, and subsequent darkening, Shalom EO offers protected silver (Ag) coatings. The silver mirror coatings are excellent for reflecting visible to infrared wavelength range.
Shalom EO also provides ultra-fast enhanced silver coatings to deliver exceptional reflectance at the wavelength range of 600-1000nm minimized chromatic dispersion for ultrafast and femtosecond pulsed lasers.
Protected Gold (Au) Mirror Coating:
Gold (Au) mirror coatings offer high reflectance for the wavelength range from NIR to IR. Its reflection upper limit can even extend up to 20μm. Protected versions are available.
