These longpass edge filters are made with hard dielectric filter coatings, producing a very steep transition between passband and stopband making them far superior to absorptive colored glass filters.
Our long wave pass filters feature both high transmission within the passband, and high rejection within the stop band, as well as a rapid transition, resulting in superior spectral isolation of a desired wavelength range. Out-of-band rejection for our longpass filters is OD≥3 and the stopband spans from X-ray to the edge wavelength. Typical transmission is ≥80% for our long-pass filters.
Our long-pass filters are available in a wide range of edge wavelengths, ranging from 385 to 1085 nm. A custom bandpass filter with excellent performance can be constructed using a combination of a shortpass and a longpass filter. These filters are available individually and in sets. The sets consist of one filter for each available edge wavelength. They are shipped in a hardwood box for convenient storage and protection.
Unlike colored glass filters, the filter edge wavelength for thin film filters will shift to shorter wavelengths with increased AOI. This can be useful for tilt tuning these filters to your exact wavelength. The shift may be calculated by: λ = λ0 ∙[ 1 – (n_0_/n_e)2∙sin2(θ) ]1/2 Where n_0 is index of the surrounding medium (1 for air) and ne is the effective index of the filter. This property can be beneficial as the filters may be intentionally tilted to either stop or allow transmission of light from lasers or light sources near the edge wavelength. Our visible and IR filters have a particularly high n_e of 2, allowing more precise wavelength tuning.