Coating Services

   


Coating Operation

 

Yorkshire Photonic Technology Ltd has a comprehensive coating facility to offer in-house coating of components from RDT Optics or a coating service for free issue materials. We have the capability to deposit a range of metal mirrors and single layer antireflection coatings as well as an electron beam equipped evaporator, able to deposit refractory metal oxide coatings. This system can also incorporate the Commonwealth MKII Kaufmann ion source for ion-assisted evaporation. Ion-assisted evaporation can give much improved adhesion, durability and increased laser induced damage thresholds for many dielectric stack designs. In addition, substrates can be processed at ambient temperatures and shift free edge positions for dichroic (edge) filters can be achieved. 

Spectrophotometry from 170nm to 1100nm (complete with integrating sphere for scatter measurements) and comprehensive thin film design software gives our engineers the capability to design coatings from scratch. YPT is also comprehensively equipped with facilities to prepare components before coating. Process dependent, our coatings meet US MIL specifications.

Coating Types:-

Antireflection (Page Top)

Single layer magnesium fluoride antireflection coatings give around 1.5% reflectance over a reasonably broad spectral range, when deposited on 1.52 index glass. When deposited on higher indices, a magnesium fluoride single layer AR can give less than 0.5% reflectance. These coatings are relatively insensitive to incidence angle and meet US MIL 675C when deposited at elevated temperatures.

Less than 0.2% reflectance can be obtained at a single wavelength for 'V' AR coatings. These coatings are usually used for specific laser wavelengths and can be designed for a range of incidence angles.

Broadband multilayer antireflection coatings give less than 0.5% average reflectance over a 250nm spectral range. Our engineers have the capability to design multilayer AR coatings for a range of substrate indices, wavelengths and incidence angles. This capability also extends to design of dual band ARs, most often used in the visible and one near infrared laser wavelength.

Mirrors (Page Top)

Mirror coatings are based around metal or dielectric thin films.

Metal mirrors are the most common and inexpensive option. They offer broad reflectance spectrums, but are soft, of poor durability and suffer from significant absorption loss. Aluminium is very versatile and durability problems can be alleviated by the use of protective overcoats of silicon monoxide or magnesium fluoride. Absorption can be reduced and reflectivity increased by enhancing dielectric multilayers deposited on top of the metal. YPT can offer both front surface and rear surface aluminium mirrors.

Where the absorption loss is unacceptable, for example in multi-pass systems, YPT can offer all-dielectric designs. These are based on high/low index dielectric films with quarter wave thicknesses. These coatings are durable, with reflectances up to 99% and have negligible absorption, however they have limited bandwidths. Contact us directly for full details.

Beamsplitters (Page Top)

Beamsplitters reflect a portion of the incident light and transmit the remainder. Most often they are used at a 45 angle of incidence, but YPT has the capability to design beamsplitters for other angles of incidence.

For simple angular insensitive requirements, metal coatings can be used as long as a relatively large amount of absorption can be accepted. All dielectric designs can give spectrally flat transmittance and reflectance curves over about a 300nm bandwidth.

Yorkshire Photonics can also offer polarising beamsplitters and beamsplitters designed specifically for cubes.

Edge Filters (Page Top)

Using a similar design to the all dielectric high reflectors, it is possible to achieve long wave or short wave pass filters for various angles of incidence.

These filters are used to reflect a portion of the incident spectrum and transmit another portion. They can be used to reflect the infrared and transmit the visible (commonly called 'hot mirrors') or transmit the infrared and reflect the visible (commonly called 'cold mirrors'). They also find application as colour filters and ultraviolet light filters.

YPT has the capability to design and manufacture these filters for a range of incidence angles.

Chromium & Nichrome (Page Top)

YPT has the capability to deposit pinhole free chromium and nichrome at optical densities up to five, with excellent adhesion and chemical etching characteristics.

Nichrome is most often used as a coating material for neutral density filters, while chromium's main application is for graticules and lighting gobos.

To achieve a pinhole free coating at the thickness required to give an OD of 5, we have developed a complicated polishing and deposition process for heat resistant glasses, optical glasses and fused silica. Yorkshire Photonics offers a coating service for free issue material as well as competitively priced coated blanks up to 120mm in diameter.

We can also offer a full service for graticule manufacture, including mask manufacture and photolithography.