10
May
PAT Roberts

Combine absorption filters to unlock capabilities

Absorption filters eliminate specific wavelengths of light as it passes through them – an alternative to thin film optical filters that is available in a variety of standard formats for different capabilities.

For example, longpass absorption filters allow long wavelengths of light to pass through (hence ‘long pass’) whereas shortpass absorption filters attenuate those longer wavelengths and instead let the shorter wavelengths through.

Optical bandpass filters are an option for very specific applications, as they can attenuate all but the selected range of wavelengths – literally allowing a specific ‘band’ of wavelengths to ‘pass’.

And finally, a neutral density filter simply reduces the intensity of all wavelengths equally for an overall dimming effect that does not favour a particular range of frequencies.

Different absorption filters come in different materials, for example glass absorption filters and optical resin absorption filters, both of which depend strongly on the thickness of the filter.

In contrast to both of these, dichroic absorption filters are not subject to the same thickness constraints and can offer an extremely sharp transition from the wavelengths that are reflected back from the filter, to those that are passed.

To unlock specific capabilities though, multiple absorption filters can be used together, either by adding a thin-film coating to an existing filter, or by cementing or laminating several filters together into a single unit.

While this can increase the thickness of the filter further overall, it also means that multiple wavelength bands can be transmitted and absorbed or reflected in turn, leading to a very specific selection of frequencies in the eventual outputted light.

At Envin Scientific we specialise in producing custom optical filters, which can combine the capabilities of standard absorption filters with additional thin-film coatings – and we are able to offer this as a quick prototype service when needed, too.

Our custom optical filters can be adjusted in other ways, for example a change in physical dimension or a bespoke designed assembly mount or polished substrate.

Dichroic absorption filters in particular offer excellent potential for modification and finished filters with minimised thickness, and we are ideally positioned to produce rapid prototypes and production runs of these to your specifications.