PBS CUBE: KEY PARAMETERS TO CONSIDER WHEN CHOOSING

PBS cubes can be specified through several key parameters. This Alien Photonics guide briefly covers each of the parameters of pbs cubes and explains why it matters to final application.

PBS cube material

Application wavelengths

UV grade Fused Silica- Alien Photonics suggested good option for ultraviolet applications (e.g. 266 nm, 343 nm, 355 nm, etc.). UVFS is often used in VIS (515, 532, 405, 633), but N-BK7 or similar glass might be good substitute as it is less expensive. For near infrared (1030, 1064, 1310, 1540 nm) wavelengths both N-BK7 and UVFS can be used. For further IR applications other materials can be used.

Material processing and quality

Different materials typically are processed differently, from cleaning to choosing correct polishing method. Some materials are easier to process than others. Furthermore, as PBS cube is both transmissive and reflective component – the inclusions inside the material volume can also impact the performance.

Index of refraction

While it might not look so important at first sight, the refraction index can limit the options for coating materials (high and low index layers). PBS cube material can impact adhesion of coating.

Price of material

The material itself can cost similarly, but the processing of material can impact the cost further. For small batches, the material can have noticeable impact on the overall price of PBS cubes. However, for larger batches the difference becomes smaller.

Dimensions of PBS cube

Alien Photonics cubes are made by combining two compatible prisms. Probably the best way to ensure that compatibility – to produce prisms at the same time (batch or lot), this would result in dimensions and tolerances as similar as possible.

Surface Quality

Polishing quality will impact pricing and performance of the PBS cube. Typically measured in scratches and digs (according to MIL standard). We recommend checking out Alien Photonics quick guide to surface quality or learning more about optical testing.

Flatness and wavefront distortion

PBS cube typically has 5 optical interfaces (4 enter – exit surfaces and 1 polarizing coating in the interface of prisms). Every surface contributes to overall wavefront distortion.

Flatness and reflective wavefront distortion

Flatness of specific surface impacts the reflected wavefront distortion. It is most important for beams that are reflected (polarizing coating on prisms hypotenuse).

Transmitted wavefront distortion

Transmitted wavefront distortion happens when beam is transmitted through the surface. This is especially important for AR coated surfaces, but also for the interface of prisms.

Combining – Glue vs optical contact

Alien Photonics PBS cubes are either optically contacted or combined using optical adhesives. Both options have some advantages and disadvantages, optical contact is for more precise applications, while adhesive option can be more economical solution. Check our guide glue or optical contact to compare.

Beam Deviation

While only the largest deviation is specified, two types of beam deviations should be taken into consideration.

Transmitted (P pol.) beam deviation

This deviation shows how beam deviates from original once it passes though the cube. The main causes are interface and how parallel are the enter and exit surfaces.

Reflected beam (S pol.) beam deviation

This deviation shows how beam deviates from theoretical 90° trajectory. The main cause is the 45° hypotenuse angle accuracy. However, 90° angle between enter and exit surfaces also has some effect.

Spectral characteristics of PBS coating

PBS cubes usually are specified by operating wavelength range, reflection (Rs) and transmission (Tp) values.

Wavelength range

PBS cubes can be designed to work at single wavelength (like low energy PBS cubes or high energy pbs cubes), two wavelengths, multiple wavelengths or fully broadband like broadband PBS cubes.

Reflection (Rs) and Transmission (Tp) values

The narrower the range, the better values can be achieved, as whole optimization priority is Rs and Tp.

Extinction ratio

While spectral characteristics might look good, extinction ratio shows how well the polarizations are separated. Alien Photonics offers standard PBS with 500:1 ratio, precision PBS cubes with 1000:1 ratio and broadband PBS with 250:1.

Laser Induced Damage Threshold - LIDT

Laser Induced Damage Threshold is another important parameter to consider. If your laser works at high powers – Alien Photonics high Energy PBS or high energy broadband PBS cube is recommended, while for low-medium power we suggest low energy PBS or low energy broadband PBS cubes

Final recommendations

Selecting the right PBS cube requires balancing several parameters depending on your specific application. If you are unsure which PBS cube fits your needs, contact Alien Photonics or browse our PBS cube selection.