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Standard Longpass & Shortpass

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 Description

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
industry_steepness

ALPHA Cut-On/Cut-Off Steepness Factor
alpha_steepness
The lowest cut-on steepness factors indicate the steepest cut-on edge.

spectral_longpass

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.

Cut-on Wavelength Tolerance:
CF ±10nm at 50% peak transmission
ALPHA ±3nm at 50% peak transmission
Average Transmission >90%
Cut-on Wavelength Temperature Dependence 0.016nm/°C to 0.026nm/°C
Construction Interference Filters Either (a) exposed, front-surface hard coating on a single-element substrate, or (b) protected soft dielectric coating in a laminated moisture-resistant assembly
Temperature of Measured Performance 20°C
Operating Temperature Range -60°C to +80°C
Humidity Resistance Per Mil-STD-810E, Method 507.3 Procedure I
Coating Substrates Optical quality glass
Surface Quality 80/50 scratch/dig per Mil-O-13830A
Outer Dimension Tolerance +0, -0.25mm (+0, -0.01”)
Minimum Clear Aperture 4mm less than nominal outside dimension
Thickness:
Unblocked Filters Unblocked filters, 1.5mm +0, -0.5
Longpass Filters Blocked, 6mm maximum
Shortpass Filters Blocked, 10mm maximum

 

Documentation

Spectrophotometric trace of the attenuation, cut-on, and transmission regions with a resolution of 0.1nm provided.