Anti-Reflection (AR) Coatings
We offer multiple forms of anti-reflection thin film coatings. The general coating we define as Anti-Reflection is a thin film deposited on a substrate that brings the reflection from the substrate down from its original value at the desired wavelength. In addition we can engineer coatings that yield lower reflection or cover wider ranges.
Broad-Band Anti-Reflection (BBAR)
We define our broad-band AR coatings as AR coatings as above, but the anti-reflection is not just at one target wavelength. Rather, it is spread across a range of wavelengths ≥100nm wide.
Ultra-Low Anti-Reflection (ULAR)
Ultra low AR coatings are high performance anti-reflection coatings. An area of Helia expertise, our ULAR thin film coatings are characterised by having ≤0.1% of incident light reflected.
High-Reflection (HR) Coatings
As with our AR range, we offer many different types of HR coatings. We find many of our customers require back-facet coatings that give 90% reflectivity, allowing the output to be monitored from behind. We can also engineer coatings to allow for active characterisation of device performance. As such our standard HR coatings have ≥90% reflectivity.
High Efficiency High-Reflection (HEHR)
Our HEHR coatings are designed for customers looking for a higher reflectivity than our standard HR coatings. We define our HEHR coatings as having ≥97% reflectivity.
Ultra-mirror coatings are another area of Helia expertise. These extreme performance coatings are classed as having at least 99.99% reflectivity, making them outstanding mirrors for low loss systems.
A metal mirror is an HR coating formed by depositing a metal. Commonly used metals are silver, aluminium and rhodium. They can be engineered to have peak reflectivity at the wavelength of interest. However, due to the reactivity of the metals they should be used in inert environments.
Protected Metal Mirror
Protected metal mirrors are almost identical to metal mirrors as above. The difference, however, is that a protective layer is deposited on the surface of the mirror. This prevents the reactivity issue described above, and offers some physical resistance against sleeks, scratches and chips.
Enhanced Metal Mirror
Following from protected metal mirrors, enhanced metallic mirrors are metallic mirrors with a dielectric HR coating stacked on top. This gives a broad wavelength performance and protection to the mirror.
Band Pass (BP)
Our band pass filters transmit light within a certain waveband and reject all other nearby wavelengths. These filters can be either wide band pass, around 100nm wide, or narrow pass which have width ≤10nm.
Short-wave pass filters are designed to transmit light with wavelengths lower than a chosen wavelength and block light with a longer wavelength. For example one could design a filter to block visible light and transmit ultra-violet, with the cut off wavelength at 400nm.
Long-wave pass filters are similar to short-wave pass filters except, as the name suggests, they pass longer wavelengths and block shorter ones.
Notch filters are used when transmission in all but a few bands is desired. Notch filters can be formed so that, for instance, all of the visible spectrum is transmitted except the blue and orange regions.
In many coatings, layers of dielectrics are stacked on top of each other. This can cause a step change in the Standing Wave Voltage Ratio (SWVR) of the electric field at the boundary of two layers. If this needs to be avoided, Rugate filters are employed.
Induced transmission filters are generally used when one wishes to pass visible light but block or reduce thermal radiation. This is achieved by designing IT filters so that they transmit in the visible region and reject infrared radiation.