Overview
Barrier or edge filters transmit only above or below a certain "cut-on" or "cut-off" wavelength and continue to transmit over a wide spectral range. These filters can be designed for use in reflection or transmission mode, and can be used as beamsplitters or combiners.
Products
For custom longpass/shortpass filters, use our Build-a-Filter request form.
Filter Descriptions
Longpass/Shortpass Filters
- Cut-On/Cut-Off Edge—the wavelength of the edge at 50% of the maximum transmission of the filter.
- Edge Steepness—the slope of the edge between reflection and transmission.
- Reflection Range—the spectral region in which the filter does not transmit.
Longpass and Shortpass Filter Types
Cut-On/Cut-Off (CF)
Typical of the industry standard, providing peak transmission of 85% to 90%, with attenuation typically 99.9% or 10-3. They have a relatively shallow slope between the reflection and transmission regions, defined as a 1-decade 3–5% slope between 85% and 5%T.
ALPHA (ALP and ASP)
ALPHA technology produces slope factors 10–50 times steeper than industry standards, with a 5-decade slope factor defined as a measurement of the distance between 50% and 0.001% transmission (or OD 5). Longpass and shortpass filters are available with edge steepness to the following values: 1% Epsilon, 3% Gamma, and 5% Beta.
Colored Absorption Glass
Manufactured using scientific glasses available from Schott, Hoya, Corning, and others. Filters are configured and polished, and are available with durable anti-reflective surface coatings.
We often use absorption glass filters to extend the attenuation range of our various filters. The best filter solutions frequently combine interference coatings laminated to any appropriate longpass or shortpass color absorption glass.
See Figure 1 for a comparison of longpass filter types.
Industry Cut-On/Cut-Off Steepness Factor
ALPHA Cut-On/Cut-Off Steepness Factor
The lowest cut-on steepness factors indicate the steepest cut-on edge.
Figure 1: Spectral Curves of Longpass Filters
A comparison of theoretical longpass filters including CF, absorption glass, and ALPHA designs at normal incidence (0°). They all have a similar cut-on wavelength at approximately 600nm.
Standard Specifications: Longpass and Shortpass Filters
The following specifications apply to all Omega Optical longpass and shortpass barrier filters unless other custom specifications are requested.
Documentation
Spectrophotometric trace of the attenuation, cut-on, and transmission regions with a resolution of 0.1nm provided.