Optical coatings. Aluminium, silver, gold and platinum

Starna Optical Coatings
Thin film coatings can be used to increase or reduce reflection from the surface of an optical component. They can be used to improve performance at a specific wavelength or over a broad wavelength band.
Optiglass now has a variety of optical coating equipment which includes electron bombarded sources with automated deposition control. In addition, the use of Thin Film Design Software enables Optiglass to offer a range of optical coatings which can be applied to any suitable optical surface. The main categories of coatings are as follows:

ANTI-REFLECTION COATING

Single Layer Anti-Reflection Coatings

Laser Line Anti-Reflection Coatings(V-Coatings)

MgF2 Single Layer AR

V-Coat @ 633 Nm

These coatings are a quarter wave optical thickness of magnesium fluoride and may be centred at any wavelength over the range 300-2500 Nm.
Reflectance is reduced to 1.5% per surface at the centre wavelength.

V-Coatings provide very low reflectance at one specific wavelength.(typically less than 0.1% per surface at the specified wavelength)
V-Coatings are available centred at any wavelength over the range 400-1200 Nm.

Broadband Multilayer Anti-Reflection Coatings

Visible Broadband AR

Cuvette Coating

some fluorescent applications require either or both the excitation and emission energy to be enhanced by applying a metallic mirror coating to the outside of adjacent windows opposite to the source and the detector windows. Similarly, anti-reflection coatings on the other windows reduce reflective losses.

This type of coating provides much lower reflectance than that obtained from a single layer of Magnesium Fluoride. This multilayer coating typically achieves less than 0.3% reflection per surface over the range 425-675 Nm.
The coating is available for other wavebands and for various refractive index of glass. In addition, dual-band coatings(e.g. visible and 1064 Nm) are available.

Type No.	Description
/AR /MC /AR/MC	Anti-reflection coating Mirror coating Anti-reflection & mirror coating

BEAM SPLITTER COATINGS

These coatings are partially reflecting and may be used where a light beam needs to be split into two. Two types of Beamsplitter are available from Optiglass.

Polka-Dot Beamsplitters

Dielectric Beamsplitters

50/50 Beamsplitter for 45 deg

These coatings are constructed from protected metal films and provide a constant reflection-transmission ratio over a very wide spectral range.

These are low absorption coatings and are useful over a more limited wavelength range. Typical reflection: transmission ratios are 50:50 and 40:60.

MULTILAYER INTERFERENCE FILTERS

Notch Filter for 633 Nm

Laser beam Splitter

These can be used to pass certain regions of the spectrum while rejecting others.
The curve shown is for a Notch Filter designed for maximum reflectance at 633Nm and low reflectance in other spectral regions.

HIGH REFLECTANCE METAL COATINGS.

Aluminium

Unprotected aluminium provides good reflectance over most regions of the spectrum but cannot be easily cleaned. Aluminium can be protected with an overcoating of silicon dioxide which enables careful cleaning to take place.

Protected Aluminium

Two versions of Protected Aluminium are available:

UV Optimised

Visible Optimised

UV Aluminium Mirror

Visible Aluminium Mirror

This provides reflection greater than 85% over the wavelength range 190-300 Nm.

This provides reflection greater than 85% over the wavelength range 400-700 Nm.

Enhanced Aluminium

Mirror Coatings

Aluminium can be overcoated with dielectric layers which increase its reflection in certain regions of the spectrum.Typical reflection is 95% average over the wavelength region 450-650 Nm.

Mirrors
available in all Glass types & Fused Silica with a variety of optical coatings.

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Email:sales@starna.co.uk