Features

• Beamsplitter Coating on Front Surface: 250 - 450 nm
• AR Coating on Back Surface: 250 - 450 nm
• Optimized for 50:50 Beamsplitting for AOI = 45^o
• Ø1/2", Ø1", 25 mm x 36 mm, and Ø2" Versions Available
• UV Fused Silica Substrate (Transmission Curve)
• Back Surface has 30 arcmin Wedge

Thorlabs' 50:50 UV Fused Silica Broadband Beamsplitters, which are available in Ø1/2" (12.7 mm), Ø1" (25.4 mm), 25 mm x 36 mm, or Ø2" (50.8 mm) versions, have one of five broadband beamsplitter coatings specifically designed for use with incident light at 45°: 250 - 450 nm, 400 - 700 nm, 700 - 1100 nm, 350 - 1100 nm, 600 - 1700 nm or 1.2 - 1.6 µm. In all cases, a dielectric coating is used for long-term stability.

These plate beamsplitters utilize a UV-grade fused silica substrate, which offers high transmission deep into the UV (down to 185 nm), good homogeneity, and a lower coefficient of thermal expansion than N-BK7. In addition, UV fused silica exhibits virtually no laser-induced fluorescence (as measured at 193 nm), making it an ideal choice for applications from the UV to the near IR.

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 our round 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 at 45^o 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% over the entire operating range of the coating. Second, the back surface of the round beamsplitters have a 30 arcmin wedge; therefore the fraction of light that does get reflected from this AR-coated surface will diverge. The edge of each round plate beamsplitter is engraved with the item number and an arrow pointing to the AR-coated surface indicating the direction of light propagation as shown on the Specs Tab.

Our 25 mm x 36 mm x 1 mm rectangular 50:50 beamsplitters are specifically desinged for mounting in microscopy filter cubes. These filters feature a beamsplitting coating on the first surface, and an AR coating on the backside of the beamsplitter to reduce unwanted reflections. The item number is engraved on the beamsplitting surface for easy optic identification as well as to simplify orienting the optic in the beam path.

Thorlabs offers three types of non-polarizing beamsplitters: Non-polarizing Beamsplitting Cubes (mounted and unmounted), Pellicle Beamsplitters (mounted and unmounted), and the Plate Beamsplitters (see below and selection guide above). For a direct comparison of the performance of our non-polarizing beamsplitting cube, plate, and pellicle at 633 nm, see the Lab Facts tab.

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Round Beamsplitter Specifications

Rectangular Beamsplitters Specifications

Above is the measured transmission (left) and reflectance (right) curves for the 50:50 broadband plate beamsplitter coated for 250 - 450 nm. Data was obtained for a 45 degree angle of incidence. The shaded region corresponds to the stated beamspitter coating range.

Click Here for Raw Data
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UV Fused Silica Transmission Data

The transmission curve to the right was obtained using a 10 mm thick, uncoated sample of UV fused silica; the incident light was normal to the surface. Please note that this is the measured transmission, including surface reflections.

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 the round versions of 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, such as interferometry, as the polka dot pattern will affect the image.

Thorlabs Lab Fact: Beamsplitter Package Matters

We present laboratory measurements of the polarization angle, split ratio, and total throughput power of a beam transmitted through Thorlabs plate, cube, and pellicle beamsplitters. While all non-polarizing beamsplitters function similarly, the exact performance is different for different types of beamsplitter. Each type of beamsplitter contains its own advantages and disadvantages compared to other types of beamsplitters. Appropriate choice of beamsplitter is essential to sensitive experimental systems. We present a complete analysis and comparison of optical parameters for three common types of non-polarizing beamsplitters.

For our experiment we used the HRS015 stabilized HeNe as the light source for our investigation. A linear polarizer is used to set the laser beam's polarization axis to 45° in order to provide equal S- and P-polarized light incident on the beamsplitter. The beamsplitter under investigation was then placed in the beampath, and its split beams directed to appropriate detectors. The total power though the optic, polarization states, split ratios, and angle of incidence effects were investigated under this configuration.

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The plots below summarize the measured results for all three types of beamsplitters. From these graphs the performance of each optic can be easily compared to one another. The bottom left plot summarizes the results for the total power throughput for each optic. The total power throughput is measured as the fraction of input power. While the plate and pellicle beamsplitters perform rather similarly, the cube shows signs of absorption inside the optic. Additionally, this plot shows the relative insensitivity of throughput power to angle of incidence. The bottom middle graph summarizes the results for the output polarization angle for each optic. The cube shows the most similar polarization angles between the reflected and transmitted beams, with the plate producing the largest difference in polarization between beams. The bottom right plot summarizes the results for the split ratio, as a fraction of input power, for the beamsplitters. Here it can be shown that the plate beamsplitter demonstrates the most ideal for 50/50 power splitting. For details on the experimental setup employed and the results summarized here, please click here.

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