Optical longpass filters are edge filters which are used to cut out wavelengths that are not required. The filter removes all wavelengths, such as UV from visible, from the desired cut off point. For example, a long pass filter with an 850nm cut off point would transmit virtually no power from the UV visible and NIR up to 850nm, beyond which the transmission would rise steeply to the filter’s peak value, generally better than 80%. Because they isolate specific wavelengths, long-pass filters are desirable in systems where they can be used to trim excess wavelengths or stray light to reduce unwanted near band emissions. Industry applications include order sorting in photometry and fluorescence.
Knight Optical supply a range of bespoke custom long-pass filters. The range over which high quality custom long-pass filters are available is from 350nm (UV) to 1.55µm (NIR) to meet the required edge cut-off, steepness of the transition, and the amount transmitted or blocked. For the dichroic filters the unwanted region is reflected.
Custom colour glass longpass filters:
Solid colour glass longpass filters are useful for selective wavelength transmission and lower wavelength absorption and therefore achieve high out of band blocking with very low transmission in short wavelengths and high transmission in the long wavelengths. Solid colour glass longpass filters are available in a range of custom options. Custom colour glass longpass filters have uniform spectral transmission properties over their entire aperture. Colour glass longpass filters are relatively cheap and very stable. A relatively large range of longpass filters are available for 280nm-1000nm long wavelength selection to produce your custom colour glass longpass filter requirement. Custom colour glass longpass filters are available in the Schott or equivalent and Hoya Colour or equivalent filter ranges and available up to 165mm squares. These can be made into custom square and rectangular apertures or to any shape and sizes with a maximum diameter of 164mm dia. Some russian and asian equivalent colour longpass filters are available in larger sheets up to 300x300mm squares. Custom colour glass longpass filters can be polished thinner achieving higher transmission. Filters can also be drilled or CNC machined or coated with antireflective coating
to decrease reflections and increase transmission further. Custom colour glass longpass filters are used in range of spectral selection scientific instrument applications, they also have high transmissions at selected wavelengths therefore ideal where the angle of incidence of the incident light cannot be tightly controlled.
Custom polyester and Wratten longpass filters: Polyester and wratten ranges of colour filters are available in a range of size options. Polyester types have the dye held in a thin sheet. Custom polyester longpass filters area available in large sheet to supply bespoke custom shapes and sizes to your specific. Large 1000mm square sheets can be supplied for your own cutting requirements as they are 0.1mm thk and can easily be cut with a sharp razor blade. Custom Polyester longpass filters are flexible so can be wrapped around cylinders for imaginative lighting designs , or supplied in ridged mounts. These custom polyester longpass filters cover the visible and NIR spectrum. Typical applications are in displays to protect from unwanted ambient light, and theatre lighting.
The colour effects within Kodak Wratten longpass colour filters are achieved using organic dyes in a gelatine material, which is not possible in colour glass. Wratten filters were originally designed for use in photography but are also used in imaging applications from industrial manufacture to medical. Whilst less robust than polyester filter, their spectral data is more accurately documented. The new range of kodak wratten 2 filters are now replacing older type wratten 1 filters which are manufactured using a ridged polymer. Wratten 2 filters are more robust and unaffected by water and moisture as gelatine type. Wratten longpass colour filters have a wide range of characteristics available and the sheets can easily be cut in the laboratory. Custom wratten longpass colour filters area available in 300x100mm sheets to supply bespoke custom shapes and sizes to your specific requirements. Typical applications are in displays to protect from unwanted ambient light, and a wide range of scientific instrumentation.
Custom dichroic longpass filters: Dichroic filters split the light into two or three bands and reflect one or more and transmit the others. Used at zero incidence they are generally used to select light of one of the primary colours. Both dichroic longpass filters and dichroic beamsplitter longwave reflecting filters are available as custom options. A huge range of dichroic filter colours are available not listed as standard on our website. These can be supplied on white float glass
or borosilicate or equivalent
substrates dependent on application. For applications where high levels of heat are transmitted from light source borosilicate or equivalent is the best option. We hold a wide range of stock in 450mm diameter substrates so can offer custom shapes and sizes at short notice. Custom dichroic longpass filter wedges can be supplied to build custom filter wheels. Custom dichroic longpass filters are widely used in LCD projectors and in some sensor systems.
Custom dichroic beamsplitter longwave reflecting filters: Dichroic beamsplitters are used to separate two spectral regions which require detection at the same time. Unlike dichroic filters, the beamsplitters are designed for use at 45° and find an application within fluorescence microscopy. Knight Optical provide a range of custom dichroic beamsplitters for longwave-reflecting. A huge range of dichroic beamsplitter longwave reflecting filters are available not listed as standard on our website. These can be supplied on white float or borosilicate substrates where high levels of heat are present. We hold a wide range of stock in 450mm diameter substrates so can offer custom shapes and sizes at short notice. Custom dichroic beamsplitter longwave reflecting filter wedges can be supplied to build custom filter wheels.
Custom cold mirrors: Cold Mirrors reflect the visible spectrum of light and transmit the near infra-red, which contains the thermal energy i.e. Heat. Cold mirrors are therefore another excellent alternative for transmitting the near infra-red spectrum. Cold mirrors have a sharp cut off between IR and Visible because they have a dielectric coating that can be controlled. Cold mirrors are often used with tungsten lamps which are the source in a projector or lighting system. We can offer a range of custom sizes shapes and sizes up to 600mm dia. Custom cold mirrors are available as 45°AOI or 0°AOI. We can supply custom shapes and sizes to your complete specification. A range of mounting options are available.
Custom Raman edge filters: Knight Optical supply custom raman edge filters for the detection of weak signals in a high noise environment. The raman effect is when an incident photon emits a phonon within a sample, and is therefore downshifted (Stokes shift) or it can absorb a phonon and be upshifted (anti-Stokes). The cross-section intensity is very small, which means that to generate the signature it is necessary to use high intensity lasers and very sensitive detection sensors and electronics. The cross section signature has another detection problem in the auto fluorescence signal from the sample. The stokes and anti-stokes shifts are very small, which means that the detection wavelength is very close to the laser wavelengths. This means that the signal needs to be extracted from the strong laser intensity. This requires a very cut-on, cut-off, edge filter with a high blocking of the laser intensity and transmits the very weak signal from the wavelength shift. The blocking of custom raman filters needs to be greater than ND6 and the edge needs to be very sharp bandwidth, such as 1nm, between the blocking and transmission region. These custom raman edge filters are available for the range of wavelengths from the UV to NIR.
Our custom longpass filters can be supplied in range of mounting options. For example custom long pass filters can be supplied to screw directly onto tamron lenses
which have a 25.5 thread on the front and similar custom solutions for lenses in fujinon range where no thread is provided.
Knight Optical supply high quality custom longpass filters made to our exact specification. Every component is individually tested on our Agilent Cary 5000 spectrometers fitted with a UMA device for testing coatings in transmission and reflection at any given angle. We also have a DRA device fitted for testing complex beamsplitter components. Our 660 FTIR spectrometer is used for coatings between 3.5µm and 45µm. All tested by our highly skilled technicians in our state of art metrology lab to ensure all components meet our high quality standards. We can provide transmission and reflection curves at given wavelengths from 175nm up to 3200nm in TXT or CSV format, or other formatted options.
Our custom long pass filter capapbility sheet can be found here: Capabilities – Long Pass Filters
Contact our multilingual technical sales team and discover how Knight Optical’s high quality custom longpass filters and service can improve your instrumentation and supply chain experience.