Cube-Mounted Pellicle Beamsplitters

Features

• Eliminates Ghosting
• No Chromatic Aberration with Focused Beams
• Minimal Change in Optical Path Length
• SM1-Threaded Entrance and Exit Ports
• 30 mm Cage System Compatible

Thorlabs' Ø1" mounted pellicle beamsplitters are ideal for use in applications where chromatic dispersion must be minimized (i.e. cases where focused beams are necessary). These beamsplitters virtually eliminate ghosting since the second surface reflection is superimposed on the first one. However, they are extremely fragile due to the nitrocellulose membrane being microns thick, which exhibits less than 1/2 wave of variation at 635 nm across its 25 mm diameter. To provide maximum protection from damage, these beamsplitters are housed inside a 30 mm cage-system-compatible cube. The cubes are post-mountable and have SM1-threaded access ports, making them compatible with our entire line of Ø1" lens tubes and accessories. The cubes are M6 x 0.5 threaded, but include 8-32 and M4 mounting adapters. These Beamsplitter cubes can also be connected to other cage cubes with cage rods and our ERSCA adapters.

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CM1-BP145B3 Shown with Two SM1CP2 Port Hole Covers (Sold Separately)

Please Note: Pellicle beamsplitters exhibit sinusoidal oscillations in the splitting ratio as a function of wavelength, due to thin film interference effects. See the Thin Film Tutorial tab for more details. These sinusoidal oscillations can be clearly seen in the plots below.

The engraving on the top of the mounts indicates the direction of incident light. This direction is consistent with the light being incident upon the coated surface of the beamsplitter first.

Thorlabs offers three types of mounted beamsplitters: Non-Polarizing Beamsplitting Cubes, Polarizing Beamsplitting Cubes, and the Pellicle Beamsplitters presented below. A large variety of unmounted beamsplitters are also available. For a direct comparison of the performance of our non-polarizing beamsplitting cube, plate, and pellicle at 633 nm, see the Lab Facts tab.

For a complete selection of our cube-mounted optics please see the Mounted Optics Guide tab.

Handling Precautions
Our pellicle beamsplitters are manufactured from an extremely thin and fragile membrane. Please do not touch the membrane under any circumstances. Compressed or canned air should also not be used on these beamsplitters, as the force of the air is large enough to damage the membrane. If the pellicle becomes damaged, please contact tech support for information about replacement of the beamsplitter; in these cases, we only charge for the cost of the pellicle.

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 former generation HRS015 stabilized HeNe laser (replaced by the HRS015B) 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 beam path, 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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30 mm Cage-Cube-Mounted Optics Selection Guide

The table below provides links to all of our 30 mm Cage-Cube-Mounted optics. For our selection of 16 mm Cage-Cube-Mounted Optics, please see our 16 mm Cage Systems guide.

Non-Polarizing Beamsplitter Cube	Polarizing Beamsplitter Cube	High-Power Polarizing Beamsplitter Cube
Pellicle Beamsplitters	Laser Line Polarizing Beamsplitter Cube	Circular / Variable Polarizers
Penta Prisms	Turning Mirrors	Variable Beamsplitters / Attenuators

30 mm Cage Cube Empty Optic Mounts Selection Guide

Rectangular Dichroic Mirrors and Filters	Empty Compact 30 mm Cage Cube

Thin-Film Interference Effect

The plots below, which show transmission as a function of wavelength, depict a sinusoidal fluctuation that is caused by interference effects. These effects will occur for all pellicle beamsplitters and are sometimes averaged out when data is displayed.

The graph to the right depicts the actual measured percent reflectance of an 8:92 beam sampler without averaging the sinusoidal oscillations that result from thin film interference. The frequency and amplitude of the pattern depends on four factors: the thickness of the film, the thickness of any coating present, the angle of incidence of the incoming light, and the polarization of the incoming light.

Q: What is a thin film?
A layer of material is referred to as a thin film if the thickness of the layer is on the order of the wavelength of incident radiation in the film medium. The relationship between the wavelength of light in air and that in the film is given by

For the pellicle beamsplitters featured here, the information under the Specs tab states that n_film = 1.5 at 550 nm. Therefore, for this incident wavelength, the wavelength in the pellicle membrane itself is