alpha-BBO Glan-Laser Polarizers
Alpha-BBO Glan-Laser Calcite Polarizers Divert P-Polarization, Leaving a Very Pure S-Polarized Beam (Aligned with the "Polarization Axis" Mark on the Housing) Passing Through the Polarizer
- Extinction Ratio: 100,000:1
- Fabricated from the Highest-Grade, Laser-Quality α-BBO
- Three Available Coatings
- 210 - 450 nm (centered at 266 nm), Ravg <1.5%
- 220 - 370 nm, Ravg < 0.5%
- VAR for 405 nm, Ravg <0.25%
- High Damage Threshold: 5 J/cm2 (10 ns pulse, 10 Hz, Ø0.347 mm Spot Size, @ 355 nm)
- Low Scatter
- Wavefront Distortion ≤ λ/8 Over Clear Aperture (Excluding Side Ports)
- Surface Quality
- 20/10 Scratch-Dig on Input and Exit Faces
- 40/20 Scratch-Dig on Side Ports
- Air-Spaced Design
The Glan-Laser α-BBO Polarizer is specifically designed to deal with high-energy, short-wavelength laser light. Like our Glan-Taylor and Glan-Laser Calcite Polarizers, these polarizers are ideal for applications requiring extremely high polarization purity (100,000:1), high damage threshold (5 J/cm2, 10 ns pulse, 10 Hz, 0.347 mm Spot Size, @ 355 nm), and transmisison in the UV (210 - 450 nm).
Two polished side exit ports are provided to allow bidirectional use of the prism polarizer. These side ports also ensure that the rejected light from high-power lasers can safely exit the polarizer. Glan-Laser Polarizers are designed to work with well collimated light beams. Divergent beams will produce multiple output beams.
The polarizers are available with three antireflection coatings: a single-layer MgF2 antireflection coating (SLAR-MgF2), a UV AR coating, or a V Coating optimized for 405 nm. The SLAR coating features good broadband UV performance with low reflectance (<1.5%) from 210 to 450 nm while the UV AR coating provides exceptionally low reflectance (<0.5%) from 220 to 370 nm. The 405 nm V coating provides even less reflectance (<0.25%) than the UV coating at 405 nm. See the Graphs tab for more information.
The input and output faces are polished to a laser quality 20-10 scratch-dig surface finish to minimize scattering of the transmitted P polarization component of the laser beam or light field. The S polarization component is reflected at a 61o angle (wavelength dependent) and exits the polarizer through one of the two side ports.
For compatibility with Thorlabs' selection of rotation mounts and other optomechanics, these polarizers can be mounted in our Polarizing Prism Mounts, which are available for both 5 mm (SM05PM5) and 10 mm polarizers (SM1PM10). Thorlabs also provides Glan-Taylor polarizers.
|Material||Laser Quality α-BBO|
|Design||High Laser Damage Threshold|
|Transmission Range||210 - 450 nm|
|Available AR Coatingsb||SLAR MgF2 (210 - 450 nm), Ravg<1.5%|
UV (220 - 370 nm), Ravg<0.5%
V-Coat (405 nm), Ravg<0.25%
|Damage Threshold||5 J/cm2 (10 Hz, Ø0.347 mm Spot Size, 10 ns Pulses @ 355 nm)|
|Wavefront Distortion||≤ λ/8 Over Clear Aperture|
|Surface Quality (Input and Output Faces)||20/10 Scratch/Dig|
|Surface Quality (Side Ports)||40/20 Scratch/Dig|
|Aperture||5 mm x 5 mm||10 mm x 10 mm|
|Prism Dimensions (W x L)||6.5 mm x 7.5 mm||12 mm x 13.7 mm|
a Extinction ratio is only for the output ray (see drawing below). Measured at 405 nm and 355 nm.
b The escape windows (perpendicular to input / exit faces) are not coated. See the Graphs Tab for more information.
Note: Since α-BBO is a relatively soft material, care must be taken when cleaning. The coated faces of the polarizer can be gently cleaned with solvent and air. The escape faces (uncoated and perpendicular to the input / exit faces) are extremely delicate and can be damaged very easily. Do not touch these faces if possible. Cleaning should be light and at a glancing angle. If these surfaces must be wiped, use only solvent-moistened cotton or untreated facial tissues.
Field of View Angle Orientation
A significant amount of scattered unpolarized light escapes the polarizers. As a result, the escape ray (o-ray) is not purely polarized and should not be used for polarization dependent applications.
The typical transmission and reflectivity of the α-BBO Glan-Laser polarizers are shown in the graphs below. The blue shading indicates the region for which the AR coating is optimized (see Specs tab for more information). The reflectivity plots represent the performance of the coating only, not including internal losses of the polarizer. The transmission plots include both both reflectivity and transmission through the polarizer (including any internal losses).
The plots below apply to the GLB10 and GLB5 α-BBO Glan-Laser polarizers.
The plots below apply to the GLB10-UV and GLB5-UV α-BBO Glan-Laser polarizers.
The plots below apply to the GLB10-405 and GLB5-405 α-BBO Glan-Laser polarizers.
Note: Short wavelength cutoff is due to the cut angle of the α-BBO prism not the reflectivity or transmission of the material.
Glan Laser Specifications
|W||6.5 mm||12 mm|
|L||7.5 mm||13.7 mm|
|A||9.5 mm||16 mm|
|B||12.7 mm||19.2 mm|
Polarization-Dependent Refraction - Glan Laser α-BBO Polarizer
Thorlabs uses only the highest quality synthetic α-BBO in our polarizing prisms. The transmission curves of the α-BBO polarizers are shown below. These curves also represent the transmission of the GLB5, GLB5-UV, and GLB5-405, respectively. Variations during the manufacturing of the α-BBO crystal affect the transmission curve and the damage threshold rating.
Thorlabs' α-BBO polarizers are all based on high-grade, birefringent, α-BBO crystals. Due to the birefringent structure of α-BBO, a differential delay is created between two orthogonally polarized waves traveling in the crystal. As shown in the image to the right, this birefringent structure creates a polarization-dependent refraction that effectively steers the polarization planes in two angles. While the extraordinary plane will travel straight through the crystal, the ordinary plane will exit the crystal at an angle proportional to the wavelength as well as the length of the crystal.
A Glan-Laser or Glan-Taylor polarizer can be designed as either a polarization splitter/combiner or as a polarizer element that removes the angled, orthogonally polarized component of a beam. Our polarizers are typically built out of two prisms, as shown in the drawing to the right. Since α-BBO is a soft crystal that is easily damaged, all of our α-BBO polarizers are offered in metal housings. With convenient threadings and adapters, these housings can easily be mounted into our opto-mechanical products.
Field of View
α-BBO polarizers feature a field of view (FOV) that varies with both wavelength and entrance orientation. The FOV of these prisms must be considered during alignment and collimation procedures. The FOV on the side which rejects the o-ray (FOV 1) has a decreasing FOV with increasing wavelength. The opposite side (FOV 2) has a FOV that increases at longer wavelengths.
Field of View Angle Orientation