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Beamsplitters & Mirrors

Dichroic Beamsplitters


Dichroic beamsplitters are longpass and shortpass filters that are used at non-normal angles of incidence. They highly reflect one specified spectral region while optimally transmitting another. Dichroics are available at all wavelengths, with reflectivity typically reaching values greater than 98% and transmission typically exceeding 85%. Dichroics are non-absorbing so that all light that is not transmitted is specularly reflected.

In most applications, the dichroic beamsplitter is oriented at 45º so that the reflected light makes an angle of 90° to the incident light, although any angle less than about 100° is possible. If the angled filter is a longpass, then the longer wavelengths will be transmitted through the filter parallel to the path of the original, incident light beam, while the shorter wavelengths will be reflected in an off-axis direction. Hence the term dichroic—two colors.

The ideal characteristics of a dichroic beamsplitter include a very sharp cut-on edge, an infinite region of transmission, and a wide region of reflection. While it is not possible to create a filter which is optimal in all three dimensions, dichroic filters can offer outstanding performance in any two of these three spectral characteristics.
Omega Optical's dichroic filters do not significantly affect the polarization of the reflected and transmitted light. In addition, filters can selectively separate the P-plane and S-plane of polarization.


  • Dichroic Beamsplitters
  • For custom dichroics, use our Build-a-Filter request form

Filter Description

Dichroic beamsplitters are defined by:

  • Cut-On Edge (LP)—the wavelength of the edge at 50% of the maximum transmission of the filter;
  • Cut-Off Edge (SP)—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;
  • Transmission Region—the spectral region in which the filter transmits;
  • Polarization—the degree of polarization of the filter.

Filter Types

Dichroic (DC)
Provide wide regions of both transmission and reflection. They exhibit a high degree of polarization along with a somewhat shallow transition slope.

Dichroic Mirror (DM)
Feature a steep transition slope, minimum polarization, a wide region of reflection, and a limited region of transmission.

Dichroic Reflector (DR)
Provide a steep transition slope, low polarization, a wide region of transmission, and a limited region of reflection.

ALPHA Dichroic Reflector (ADR)
ALPHA technology produces longpass and shortpass filters with slope factors 10–50 times steeper than industry standards. Edge steepness is available at a 5-decade slope factor, defined as the slope between 50% and .001%T (or OD 5), in the following values: 1% Epsilon, 3% Gamma, and 5% Beta.

Extended Reflection (XR)
Any dichroic design above can be manufactured with a secondary dielectric reflector to extend the range of reflection.


Figure 1: Spectral Curves of Dichroic Beamsplitters
Spectral trace measurements of DC, DM, DR, and ALPHA dichroic beamsplitters used at a 45¡ angle of incidence, all having a similar cut-on wavelength of approximately 55Onm. Note the differences in edge steepness, transmission, and reflection range.

Cube Beamsplitters
Cube beamsplitters provide highly efficient polarization of the incident beam. They also eliminate undesired ghost images of the reflected beam and the lateral displacement of the transmitted beam. Cube beamsplitters are made by coating the hypotenuse of a right angle prism and then cementing it to the hypotenuse of another right angle prism. Any type of filter in our product line is available in a polarizing cube configuration.

Matrix Beamsplitters
Matrix beamsplitters are designed so that regions of transmission and reflection are arranged in a spatial pattern over the surface of the beamsplitter, allowing a matrix of the beam of light to pass. The ratio of transmission to reflection (%T/%R), as with BS filters, can be any value from 99/1 to 1/99, with 50/50 being the most common.

Mirrors and Partial Mirrors


Mirrors and partial mirrors reflect uniformly over a broad spectral range. Partial mirrors work at off-normal angles of incidence reflecting only a portion of the incident light while transmitting the remainder.

Beamsplitter (BS) Filters
Can be produced to perform across ranges as wide as 700nm. Performance can be located anywhere in the spectral region from 240nm–20,000nm. The ratio of the transmitted light to reflected light (%T/%R) can be any value between 99/1 to 1/99, with typical products including ratios of 50/50, 70/30, and 30/70.

Total Reflector (TR) Mirrors
Reflect 92–99% over their primary spectral region. They are made with a variety of metal coatings—including aluminum, gold, silver, and special alloys—that are over- coated with a protective thin film.

Maximum Reflector (MR) Mirrors
Reflect greater than 99% over a somewhat narrower spectral region. Made with multiple layers of dielectric materials, they absorb virtually none of the light within the spectral region of design.

Standard Specifications: Dichroic Beamsplitters and Mirrors
The following specifications apply to all Omega Optical dichroic beamsplitters, mirrors, and partial mirrors unless other custom specifications are requested.

Cut-on Wavelength Tolerance ±5nm (except DC ±10nm)
Average Transmission >80%
Minimum Peak Reflection 85%
Cut-on Wavelength Temperature Dependence 0.016nm/°C to 0.026nm/°C
Construction Exposed, front-surface hard coating on an optical quality substrate
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
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 0.75 to 2.60mm



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