Features

• IR Fused Silica Substrate (See Graphs tab for Transmission)
• Ø1/2", Ø1", and Ø2" Versions Available
• Optimized for 50:50 Beamsplitting for AOI = 45^o
• Beamsplitter Coating on Front Surface: 0.9 - 2.6 µm
• AR Coating on Back Surface: 0.9 - 2.6 µm
• Back Surface has 30 arcmin Wedge

Thorlabs' 50:50 IR Fused Silica Broadband Beamsplitters, which are available in Ø1/2" (12.7 mm), Ø1" (25.4 mm), or Ø2" (50.8 mm) versions, feature a 0.9 - 2.6 µm beamsplitter coating optimized for an incidence angle of 45°. A dielectric coating provides long-term stability.

These plate beamsplitters utilize a IR-grade fused silica substrate, which offers high transmission from 0.9 - 2.6 µm, good homogeneity, and a lower coefficient of thermal expansion than N-BK7.

To help reduce unwanted interference effects (e.g., ghost images) caused by the interaction of light reflected from the front and back surfaces of the optic, two features have been added to these broadband plate beamsplitters. First, an antireflection coating, which is designed for the same operating wavelength range as the beamsplitter coating on the front surface, has been deposited onto the back surface. Approximately 4% of the light incident on an uncoated substrate will be reflected; by applying an AR coating to the back side of the beamsplitter, this percentage is reduced to an average of less than 1.5% over the entire operating range of the coating. Second, the back surface of the beamsplitter has a 30 arcmin wedge; therefore the fraction of light that does get reflected from this AR-coated surface will diverge. The edge of each plate beamsplitter is engraved with the part number and an arrow pointing to the AR-coated surface indicating the direction of light propagation as shown on the Specs Tab.

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*@ 635 nm Over the Clear Aperture

These plots show the measured reflectance (left) and transmission (right) curves for the 50:50 broadband plate beamsplitter coated for 0.9 - 2.6 µm. Data wasobtained for a 45 degree angle of incidence.

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Click to download Reflectance Data

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Click to download Transmission Data

These plots show the measured reflectance (left) and transmission (right) curves over visible wavelengths. Data was obtained for a 45 degree angle of incidence. This is representative data; performance will vary significantly from lot to lot outside of the designated wavelength range (0.9 - 2.6 µm).

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Click to download Reflectance Data

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Click to download Transmission Data

IR Fused Silica Transmission Data

The transmission curve shown below was obtained using a 5 mm thick, uncoated sample of IR fused silica; this incident light was normal to the surface. Please note that this is the measured transmission, including surface reflection.

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Beamsplitter Selection Guide

Thorlabs offers five main types of beamsplitters: Pellicle, Cube, Plate, Economy, and Polka Dot. Each type has distinct advantages and disadvantages.

Pellicle Beamsplitters - Pellicle beamsplitters are the best choice when dispersion must be kept to a minimum. They virtually eliminate multiple reflections commonly associated with thicker glass beamsplitters, thus preventing ghosting. In addition, unlike plate beamsplitters, there is a negligible effect on the propagation axis of the transmitted beam with respect to the incident beam.

Pellicle beamsplitters have two disadvantages: They exhibit sinusodial oscillations in the splitting ratio as a function of wavelength, due to thin film interference effects. Click Here for more details. They are also extremely delicate. Since they are fabricated by stretching a nitrocellulose membrane over a flat metal frame, the beamsplitter cannot be touched without destroying the optic. Thorlabs offers pellicle beamsplitters mounted in metal rings for use in kinematic mounts as well as cage cube mounted pellicles.

Beamsplitting Cubes
Thorlabs’ beamsplitter cubes are composed of two right-angled prisms. A dielectric coating, which is capable of reflecting and transmitting a portion of the incident beam, is applied to the hypotenuse surface. Since there is only one reflecting surface, this design inherently avoids ghost images, which sometimes occur with plate-type beamsplitters. Antireflection coatings are available on the entrance and exit faces of certain models to minimize back reflections. As well as providing a cost-effective solution, another advantage of the beamsplitting cube is the minimal shift it causes to the path of the transmitted beam. Thorlabs offers both polarizing and nonpolarizing beamsplitting cubes, in mounted and unmounted configurations, the former being compatible with our 30 mm cage systems.

Polarizing Beamsplitting Cubes - Thorlabs’ polarizing beamsplitter cubes split randomly polarized beams into two orthogonal, linearly polarized components (S and P), as shown in the diagram to the right. S-polarized light is reflected at a 90° angle with respect to the incident beam while P-polarized light is transmitted. Polarizing beamsplitting cubes are useful in applications where the two polarization components are to be analyzed or used simultaneously. Thorlabs offers mounted and unmounted polarizing beamsplitter cubes.

Nonpolarizing Beamsplitting Cubes - These cubes provide a 50:50 splitting ratio that is nearly independent of the polarization of the incident light. The low polarization dependence of the metallic-dielectric coating allows the transmission and reflection for S- and P-polarization states to be within 10% of each other. These beamsplitters are particularly useful with randomly polarized lasers and are specifically designed for applications in which polarization effects must be minimized. Thorlabs offers mounted and unmounted beamsplitter cubes.

Plate Beamsplitters - Thorlabs' plate beamsplitters are optimized for an incidence angle of 45° and feature a dielectric coating on the front surface for long-term stability. To help reduce unwanted interference effects (e.g., ghost images) caused by the interaction of light reflected from the front and back surfaces of the optic, a wedge has been added to these beamsplitters. Dispersion, ghosting, and shifting of the beam may all be potential problems, however. These are the best choice for a general-purpose beamsplitter. Thorlabs offers both polarizing and nonpolarizing plate beamsplitters.

Economy Beamsplitters - These are the most cost effective of all the beamsplitter types. Thorlabs' economy beamsplitters, which have an exposed oxide coating on one side and are uncoated on the other side, are designed to have either a 50:50 or 30:70 splitting ratio throughout the visible spectrum (450 - 650 nm) when used with unpolarized light incident at 45°.

Please note that the Fresnel reflections off of the uncoated back surface of these economy beamsplitters can lead to interference effects in the reflected beam. For applications sensitive to these effects, consider using a beamsplitting cube or a pellicle beamsplitter.

Polka Dot Beamsplitters - This type of beamsplitter consists of a glass substrate with a vacuum-deposited reflective coating that is applied over an array of apertures, giving the beamsplitter a "polka dot" appearance. Half of the incident beam is reflected from the coating, and half of the beam is transmitted through the uncoated portion of the substrate.

Polka dot beamsplitters are useful over a wide wavelength range and are negligibly angle sensitive, which makes them ideal for splitting the energy emitted from a radiant source. These are not recommended for imaging applications, as the polka dot pattern will affect the image.