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Double Glan-Taylor Calcite Polarizers


  • Excellent for Use with Broadband Sources
  • Compatible with SM1-Compatible Optomechanics
  • Extinction Ratio Greater than 100 000:1

DGL10

DGL10 Polarizer Mounted in an SM1L20 Ø1"
Lens Tube and PRM1 Rotation Mount

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Specifications
Extinction Ratioa 100 000:1
Substrate Laser Quality Natural Calciteb
Designc Air-Spaced Design for Maximum
Laser Damage Threshold
Wavefront Distortion ≤λ/4 Over Clear Aperture
Quality of Input
and Output Faces
20-10 Scratch-Dig Surface
Transmission Range 350 nm - 2.3 µm
Damage Thresholdc 20 J/cm2 (1064 nm, 10 ns, 10 Hz, Ø0.433 mm)
Mechanical Aperture 12 mm x 12 mm
Clear Aperturec 9 mm x 9 mm
Housing Diameter 25.4 mm
Housing Length 33 mm
  • The extinction ratio (ER) is the ratio of the maximum transmission of a sufficiently linearly polarized signal when the polarizer’s axis is aligned with the signal to the minimum transmission when the polarizer is rotated by 90°.
  • Click Link for Detailed Specifications on the Substrate
  • Care should be taken to ensure that the polarizer's clear aperture is large enough for your beam, and that the polarizer is well aligned. While each polarizer is air-spaced within the clear aperture, the prisms composing the polarizer are separated by an epoxied photo-etched spacer that is not designed to withstand high laser powers. Using these parts outside of the clear aperture can result in catastrophic damage and failure.
Warning: Calcite is a temperature-sensitive crystal and will crack if it is exposed to thermal shock. Allow the shipping packaging to reach complete thermal equilibrium before opening (6 - 8 hours).

Features

  • Extinction Ratio of 100 000:1
  • Large, Symmetric Field of View (FOV)
  • Triple Prism, Air-Spaced Design
  • 0.35 - 2.3 μm Transmission Range
  • Laser Quality, Low Scatter, Natural Calcite

Our Double Glan Taylor Polarizers offer an ideal solution for high-quality polarization with extinction ratios greater than 100 000:1 for laser beams in the 0.35-2.3 μm wavelength range. These triple prism, air-spaced polarizers are made from the highest optical grade of calcite. Unpolarized light enters the polarizer and is split at the two internal interfaces between crystals. The ordinary rays are reflected at each interface, causing them to be scattered and partially absorbed by the polarizer housing. The extraordinary rays pass straight through the polarizer, providing a polarized output.

The triple prism design of the polarizer gives it a larger field of view (FOV) than standard Glan-Taylor polarizers. Unlike standard Glan-Taylor designs, this double Glan-Taylor prism also has a symmetric FOV. This polarizer is only 33 mm long and features a large clear aperture that measures 9 mm x 9 mm.

The DGL10 is compatible with our Ø1" optomechanical mounting hardware. Ø1" Stackable Lens Tubes can be used to mount the DGL10 in our manual, motorized, high precision, or cage system rotation mounts.

Zemax Files
Click on the red Document icon next to the item numbers below to access the Zemax file download. Our entire Zemax Catalog is also available.
Specifications
Extinction Ratioa 100 000:1
Substrate Laser Quality Natural Calciteb (see Calcite tab)
Design Air-Spaced Design for Maximum Laser Damage Threshold
Wavefront Distortion ≤λ/4 Over Clear Aperture
Quality of Input and Output Faces 20-10 Scratch-Dig Surface
Transmission Range 350 nm - 2.3 µm
Damage Thresholdc 20 J/cm2 (1064 nm, 10 ns, 10 Hz, Ø0.433 mm)
Aperture 12 mm x 12 mm
Clear Aperturec 9 mm x 9 mm
Housing Diameter 25.4 mm
Housing Length 33 mm
  • The extinction ratio (ER) is the ratio of the maximum transmission of a sufficiently linear polarized signal when the polarizer’s axis is aligned with the signal to the minimum transmission when the polarizer is rotated by 90°.
  • Click Link for Detailed Specifications on the Substrate
  • Care should be taken to ensure that the polarizer's clear aperture is large enough for your beam, and that the polarizer is well aligned. While each polarizer is air-spaced within the clear aperture, the prisms composing the polarizer are separated by an epoxied photo-etched spacer that is not designed to withstand high laser powers. Using these parts outside of the clear aperture can result in catastrophic damage and failure.
Polarization-Dependent Refraction - Glan-Laser Calcite Polarizer
Calcite Polarization

General

Our calcite polarizers are all based on high-grade, birefringent calcite crystals. Due to the birefringent nature of calcite, waves polarized in the direction of the optical axis propagate with a different index of refraction than waves polarized orthogonally to the optical axis. In our Double Glan-Taylor polarizers, this birefringence causes the selective reflection and absorption of one polarization state of an incident beam and the transmission of the other orthogonal polarization state. When unpolarized light is incident on the optic, extraordinary rays travel straight through the polarizer, while ordinary rays are reflected at each crystal interface within the polarizer. The reflected ordinary rays are then scattered and partially absorbed by the optic's housing, resulting in a highly polarized output.

A calcite 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 calcite polarizers are typically built out of two prisms, as shown in the drawing to the right. Since calcite is a soft crystal that is easily damaged, almost all of our calcite 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

Calcite 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. Unlike standard Glan-Taylor polarizers, our double Glan-Taylor polarizers have a symmetric field of view that increases with increasing wavelength.

Transmission

Thorlabs uses only the highest quality natural calcite in our polarizing prisms. Because calcite is a naturally occuring material, variations in the crystal affect the transmission curve and the damage threshold rating. Variations in the calcite transmission curve are typically limited to wavelengths > 2 μm, making calcite an excellent material to use in the visible and NIR.

Thorlabs' Calcite Polarizers
Glan-Laser Polarizers Glan-Taylor Polarizers Wollaston Polarizers
Glan-Thompson Polarizers
Mounted or Unmounted
Double Glan-Taylor Polarizer Beam Displacers
Frame B
lens tube mounted to PRM1
Frame A
inserting lens tube in PRM1
secure polarizer's position by using spanner wrench
Frame D
inserting polarizer in lens tube
Frame C

Mounting the DGL10

The DGL10 polarizer can be mounted to a PRM1 rotation mount by using a SM1L20 lens tube:

  1. Remove the SM1RR retaining ring that comes with the PRM1 rotation mount.
  2. Screw the threaded end of the lens tube into the rotation mount as shown in Frame A.
  3. Once the lens tube is threaded (Frame B), insert the mounted polarizer into the other end of the lens tube (see Frame C).
  4. Secure the polarizer into place using the retaining ring included with the lens tube.
  5. A SPW602 spanner wrench can be used to tighten the retaining ring (Frame D).

Note: The SM1P1 Ø1" to SM1 adapter can be used in place of the SM1L20 lens tube when space is not available for the extra length of the lens tube.

Damage Threshold Specifications
Coating Designation
(Item # Suffix)
Damage Threshold
(Uncoated) 20 J/cm2 (1064 nm, 10 ns, 10 Hz, Ø0.433 mm)

Damage Threshold Data for Thorlabs' Double Glan-Taylor Calcite Polarizers

The specifications to the right are measured data for Thorlabs' Double Glan-Taylor Calcite Polarizers.

Care should be taken to ensure that the polarizer's clear aperture is large enough for your beam, and that the polarizer is well aligned. While each polarizer is air-spaced within the clear aperture, the prisms composing the polarizer are separated by an epoxied photo-etched spacer that is not designed to withstand high laser powers. Using these parts outside of the clear aperture can result in catastrophic damage and failure.

 

Laser Induced Damage Threshold Tutorial

The following is a general overview of how laser induced damage thresholds are measured and how the values may be utilized in determining the appropriateness of an optic for a given application. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. The LIDT for an optic greatly depends on the type of laser you are using. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. Note that the guideline presented here assumes room temperature operation and optics in new condition (i.e., within scratch-dig spec, surface free of contamination, etc.). Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. For more information on cleaning optics, please see our Optics Cleaning tutorial.

Testing Method

Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.

First, a low-power/energy beam is directed to the optic under test. The optic is exposed in 10 locations to this laser beam for 30 seconds (CW) or for a number of pulses (pulse repetition frequency specified). After exposure, the optic is examined by a microscope (~100X magnification) for any visible damage. The number of locations that are damaged at a particular power/energy level is recorded. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. This process is repeated until damage is observed. The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. A histogram such as that below represents the testing of one BB1-E02 mirror.

LIDT metallic mirror
The photograph above is a protected aluminum-coated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm2 (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage.
LIDT BB1-E02
Example Test Data
Fluence # of Tested Locations Locations with Damage Locations Without Damage
1.50 J/cm2 10 0 10
1.75 J/cm2 10 0 10
2.00 J/cm2 10 0 10
2.25 J/cm2 10 1 9
3.00 J/cm2 10 1 9
5.00 J/cm2 10 9 1

According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, Ø0.803 mm). Please keep in mind that these tests are performed on clean optics, as dirt and contamination can significantly lower the damage threshold of a component. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances.

Continuous Wave and Long-Pulse Lasers

When an optic is damaged by a continuous wave (CW) laser, it is usually due to the melting of the surface as a result of absorbing the laser's energy or damage to the optical coating (antireflection) [1]. Pulsed lasers with pulse lengths longer than 1 µs can be treated as CW lasers for LIDT discussions.

When pulse lengths are between 1 ns and 1 µs, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). Absorption is either due to an intrinsic property of the optic or due to surface irregularities; thus LIDT values are only valid for optics meeting or exceeding the surface quality specifications given by a manufacturer. While many optics can handle high power CW lasers, cemented (e.g., achromatic doublets) or highly absorptive (e.g., ND filters) optics tend to have lower CW damage thresholds. These lower thresholds are due to absorption or scattering in the cement or metal coating.

Linear Power Density Scaling

LIDT in linear power density vs. pulse length and spot size. For long pulses to CW, linear power density becomes a constant with spot size. This graph was obtained from [1].

Intensity Distribution

Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. Unfortunately, this is highly dependent on factors such as absorption and thermal diffusivity, so there is no reliable method for determining when a high PRF laser will damage an optic due to thermal effects. For beams with a high PRF both the average and peak powers must be compared to the equivalent CW power. Additionally, for highly transparent materials, there is little to no drop in the LIDT with increasing PRF.

In order to use the specified CW damage threshold of an optic, it is necessary to know the following:

  1. Wavelength of your laser
  2. Beam diameter of your beam (1/e2)
  3. Approximate intensity profile of your beam (e.g., Gaussian)
  4. Linear power density of your beam (total power divided by 1/e2 beam diameter)

Thorlabs expresses LIDT for CW lasers as a linear power density measured in W/cm. In this regime, the LIDT given as a linear power density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size, as demonstrated by the graph to the right. Average linear power density can be calculated using the equation below. 

The calculation above assumes a uniform beam intensity profile. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right).

Now compare the maximum power density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. A good rule of thumb is that the damage threshold has a linear relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 10 W/cm at 1310 nm scales to 5 W/cm at 655 nm):

CW Wavelength Scaling

While this rule of thumb provides a general trend, it is not a quantitative analysis of LIDT vs wavelength. In CW applications, for instance, damage scales more strongly with absorption in the coating and substrate, which does not necessarily scale well with wavelength. While the above procedure provides a good rule of thumb for LIDT values, please contact Tech Support if your wavelength is different from the specified LIDT wavelength. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application. 

Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). Testing may result in additional costs or lead times. Contact Tech Support for more information.

Pulsed Lasers

As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Pulsed lasers often do not heat the optic enough to damage it; instead, pulsed lasers produce strong electric fields capable of inducing dielectric breakdown in the material. Unfortunately, it can be very difficult to compare the LIDT specification of an optic to your laser. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values.

Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. In this ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism [2]. In contrast, pulses between 10-7 s and 10-4 s may cause damage to an optic either because of dielectric breakdown or thermal effects. This means that both CW and pulsed damage thresholds must be compared to the laser beam to determine whether the optic is suitable for your application.

Pulse Duration t < 10-9 s 10-9 < t < 10-7 s 10-7 < t < 10-4 s t > 10-4 s
Damage Mechanism Avalanche Ionization Dielectric Breakdown Dielectric Breakdown or Thermal Thermal
Relevant Damage Specification No Comparison (See Above) Pulsed Pulsed and CW CW

When comparing an LIDT specified for a pulsed laser to your laser, it is essential to know the following:

Energy Density Scaling

LIDT in energy density vs. pulse length and spot size. For short pulses, energy density becomes a constant with spot size. This graph was obtained from [1].

  1. Wavelength of your laser
  2. Energy density of your beam (total energy divided by 1/e2 area)
  3. Pulse length of your laser
  4. Pulse repetition frequency (prf) of your laser
  5. Beam diameter of your laser (1/e2 )
  6. Approximate intensity profile of your beam (e.g., Gaussian)

The energy density of your beam should be calculated in terms of J/cm2. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. In this regime, the LIDT given as an energy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. This calculation assumes a uniform beam intensity profile. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. For reference a Gaussian beam typically has a maximum energy density that is twice that of the 1/e2 beam.

Now compare the maximum energy density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately [3]. A good rule of thumb is that the damage threshold has an inverse square root relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 1 J/cm2 at 1064 nm scales to 0.7 J/cm2 at 532 nm):

Pulse Wavelength Scaling

You now have a wavelength-adjusted energy density, which you will use in the following step.

Beam diameter is also important to know when comparing damage thresholds. While the LIDT, when expressed in units of J/cm², scales independently of spot size; large beam sizes are more likely to illuminate a larger number of defects which can lead to greater variances in the LIDT [4]. For data presented here, a <1 mm beam size was used to measure the LIDT. For beams sizes greater than 5 mm, the LIDT (J/cm2) will not scale independently of beam diameter due to the larger size beam exposing more defects.

The pulse length must now be compensated for. The longer the pulse duration, the more energy the optic can handle. For pulse widths between 1 - 100 ns, an approximation is as follows:

Pulse Length Scaling

Use this formula to calculate the Adjusted LIDT for an optic based on your pulse length. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. Keep in mind that this calculation is only used for pulses between 10-9 s and 10-7 s. For pulses between 10-7 s and 10-4 s, the CW LIDT must also be checked before deeming the optic appropriate for your application.

Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. Contact Tech Support for more information.


[1] R. M. Wood, Optics and Laser Tech. 29, 517 (1998).
[2] Roger M. Wood, Laser-Induced Damage of Optical Materials (Institute of Physics Publishing, Philadelphia, PA, 2003).
[3] C. W. Carr et al., Phys. Rev. Lett. 91, 127402 (2003).
[4] N. Bloembergen, Appl. Opt. 12, 661 (1973).


Posted Comments:
youngwookjun  (posted 2017-07-25 19:42:29.413)
I also observed beam displacement while rotating the laser beam. My application is very sensitive to the beam displacement, so do you have any other recommendation of polarizer eliminating beam displacement?
tfrisch  (posted 2017-09-05 04:05:00.0)
Hello, thank you for contacting Thorlabs. It would be helpful to know if this deviation is linear or angular. I will reach out to you directly about your application.

Polarizer Selection Guide

Thorlabs offers a diverse range of polarizers, including wire grid, film, calcite, alpha-BBO, rutile, and beamsplitting polarizers. Collectively, our line of wire grid polarizers offers coverage from the visible range to the beginning of the Far-IR range. Our nanoparticle linear film polarizers provide extinction ratios as high as 100 000:1. Alternatively, our other film polarizers offer an affordable solution for polarizing light from the visible to the Near-IR. Next, our beamsplitting polarizers allow for use of the reflected beam, as well as the more completely polarized transmitted beam. Finally, our alpha-BBO (UV), calcite (visible to Near-IR), rutile (Near-IR to Mid-IR), and yttrium orthovanadate (YVO4) (Near-IR to Mid-IR) polarizers each offer an exceptional extinction ratio of 100 000:1 within their respective wavelength ranges.

To explore the available types, wavelength ranges, extinction ratios, transmission, and available sizes for each polarizer category, click More [+] in the appropriate row below.

Wire Grid Polarizers
Film Polarizers
Beamsplitting Polarizers
alpha-BBO Polarizers
Calcite Polarizers
Quartz Polarizers
Magnesium Fluoride Polarizers
Yttrium Orthovanadate (YVO4) Polarizers
Rutile Polarizers
  • Click on the graph icons in this column to view a transmission curve for the corresponding polarizer. Each curve represents one substrate sample or coating run and is not guaranteed.
  • Mounted in a protective box, unthreaded ring, or cylinder.
  • Available unmounted or in an SM05-threaded (0.535"-40) mount that indicates the polarization axis.
  • Available unmounted or in an SM1-threaded (1.035"-40) mount that indicates the polarization axis.
  • Available unmounted or mounted in cubes for cage system compatibility.
  • Calcite's transmittance of light near 350 nm is typically around 75% (see Transmission column).
  • Available unmounted or in an unthreaded Ø1/2" housing.
  • The transmission curves for calcite are valid for linearly polarized light with a polarization axis aligned with the mark on the polarizer's housing.
  • The 1064 nm V coating corresponds to a -C26 suffix in the item number.
  • Available unmounted or mounted in a protective box or unthreaded cylinder that indicates the polarization axis.
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DGL10Double Glan-Taylor Polarizer
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