Coating Range	Damage Threshold
420 - 680 nm	2 J/cm² at 532 nm, 10 ns, 10 Hz
620 - 1000 nm	2 J/cm² at 810 nm, 10 ns, 10 Hz
900 - 1300 nm	2 J/cm² at 1064 nm, 10 ns, 10 Hz
1200 - 1600 nm	5 J/cm² at 1542 nm, 10 ns, 10 Hz

Coating and Cement Layer Not to Scale

Features

30 mm Cage and SM1 Lens Tube Compatible Mounts
Wavelength Ranges from 420 to 1600 nm
Extinction Ratio

T_P:T_S > 1000:1
R_s:R_p ~ 100:1

The polarizing beamsplitting cubes on this page have a dielectric coating along the diagonal interface between the two right angle prisms that make up the cube. This coating reflects S-polarized light, while transmitting P-polarized light.

For highest polarization purity, use the transmitted beam, which offers a 1,000:1 (T_p:T_s) extinction ratio. As a guideline, the reflected beam will have an extinction ratio of roughly 100:1. The entrance and exit faces of this cube have broadband antireflective coatings that minimize losses due to reflections. The dielectric beamsplitting coating is applied to the hypotenuse of one of the two prisms that make up the cube. Then, cement is used to bind the two prism halves together. In order to achieve the desired 50:50 split ratio, the light must enter through the entrace face, as depicted by the engraving on the mount (similar to that shown to the right).

	CM1-PBS251	CM1-PBS252	CM1-PBS253	CM1-PBS254
AR-Coating Range	420 - 680 nm	620 - 1000 nm	900 - 1300 nm	1200 - 1600 nm
AR Coating (0° Incident Angle)	R_avg < 0.5%	R_avg < 0.5%	R_avg < 0.5%	R_avg < 0.5%
Ports	4 Ports With SM1 (1.035"-40) Thread
Beamsplitter Material	N-SF1
Extinction Ratio	T_p:T_s >1,000:1
Transmission Efficiency*	T_p > 90%
Reflection Efficiency*	R_s > 99.5%
Transmitted Beam Deviation	<5 arcmin
Reflected Beam Deviation	90° ± 20 arcmin
Clear Aperture	>80% of Dimension
Surface Flatness	λ/10 @ 633 nm
Wavefront Distortion**	<λ/4 @ 633 nm
Durability	MIL-M-13508C, MIL-C-675C, MIL-C-14806
Surface Quality	40-20 Scratch-Dig

* Transmission and reflection data is based on that of the beamsplitter coating and does not account for the BBAR surface coating.
** Wavefront distortion is for both transmitted and reflected beams.

Thorlabs offers three types of mounted beamsplitters: Polarization Insensitive Beamsplitting Cubes, Polarizing Beamsplitting Cubes (presented below), and the Pellicle Beamsplitters. A large variety of unmounted beamsplitters are also available.

Click to Enlarge

Legend for Beam Diagrams

Reflected Beam:

Transmitted Beam:

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 Beamsplitter

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.