Glass Absorption Optical Filters

 Glass absorption filters make use of the physical characteristics of different types of glass to absorb unwanted wavelengths of light and pass only the desired frequencies through as output.

 They have numerous different applications, for example transmitting specific colours of visible light, attenuating all wavelengths equally, absorbing ultraviolet (UV) light or removing infrared (IR) wavelengths to act as a heat filter.

 It is common to use Schott nomenclature to describe the different types of glass used; however, Envin Scientific glass absorption filters are also manufactured using equivalent glass types from suppliers such as Hoya, Kopp and others.

 Types of Schott glass filters

 Schott nomenclature categorises coloured glass filters into several groups, which Envin Scientific are able to supply.

 Some of the types of Schott glass filters we can supply include:

•         BG: Blue, blue-green and multi-band glass.
•         GG: Near-colourless/slightly yellow glass that transmits IR.
•         KG: Near-colourless glass with high visible transmission and IR absorption.
•         NG: Neutral density glass that attenuates evenly across the visible spectrum.
•         OG: Orange glass that transmits IR.
•         RG: Red/black glass that transmits IR.
•         UG: Black and blue glass that transmits UV.
•         VG: Green glass for visible longpass filters.
•         WG: Colourless glass that transmits visible and IR but cuts off UV.

 We are able to supply glass absorption filters that match these Schott glass types and equivalents from other suppliers, to produce the best filter for your application.

 Applications for glass absorption filters

 Different Schott glass types and their equivalents from other manufacturers are suited to different types of glass absorption filters and specific applications.

 In general, we use the following Schott glass types for the following general applications:

• UV Bandpass: UG
• Visible Bandpass: BG and VG
• UV and Visible Longpass: GG, OG, RG and WG
• IR Pass / Visible Block: RG
• Neutral Density Filters: NG

All of our glass absorption filter types can be manufactured to a variety of different sizes and thicknesses,including: shortpass, bandpass & longpass filters and are finished to a high degree of accuracy for very precise applications. 

A longpass Filter is an optical interference or coloured glass filter that attenuates shorter wavelengths and transmits longer wavelengths over the active range of the target spectrum. Meanwhile a shortpass filter attenuates and transmits longer wavelengths.

Bandpass filters only transmit a certain wavelength band, and block others. The width of such a filter is expressed in the wavelength range it lets through. 

Neutral density filters have a constant attenuation across the range of visible wavelengths, and reduce the intensity of light by reflecting or absorbing a portion of it. They are specified by the optical density of the filter.

Other types of absorption filters

Absorbing glass filters are just one type of absorption filter designed & manufactured by Envin Scientific, and can be used alone or in combination with other coated filters for a variety of even more specific effects.

 Some of the other types of absorption filters we supply include:

• Dichroic Absorption Optical Filters
• Laminated Absorption Optical Filters
• Resin Absorption Optical Filters
• Bandpass Optical Thin Film Filters
• Notch Optical Filters (Minus Filters)     

These work using the physical properties of dichroic materials, non-glass resin and/or surface coatings to achieve effects that complement those of glass filters.

Dichroic filters exact colour range can be controlled by the thickness and sequence of the coatings.Through a series of coated optical filters they can be used in devices such as the dichroic prism of a camera to separate a beam of light into different coloured components. Envin offer a range of Dichroic Absorption Filters (DAF) which closely match, or exceed, the performance of light absorbing filters but without the thickness constraint.

Laminated filters in particular can layer glass and other materials with optical cements, polarising films, thin films and gels for truly unique performance characteristics overall.

Notch Filters or ‘Minus Filters’ are used to remove selected unwanted wavelengths, such as laser lines, by reflection.

You can find out more about each of these types of absorption filters by looking around our website, or please contact us if you have any specific questions or enquiries about any of our optical filters for visible, IR and UV light.

Or if you have a particular application in mind that you would like to discuss, contact Envin Scientific today and we can help you to choose the best absorption filter for the job.