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Silicon Windows


  • Offered Uncoated or with AR Coating for 3 - 5 µm
  • Ø1/2" and Ø1" Sizes Available

WG81050-E

(Ø1")

WG81050

(Ø1")

WG80530-E

(Ø1/2")

WG80530

(Ø1/2")

Related Items

Precision Window Selection Guide
Wavelength RangeSubstrate Material
120 nm - 6 μmMagnesium Fluoride (MgF2)
150 nm - 5 μmSapphire
180 nm - 8 μmCalcium Fluoride (CaF2)
185 nm - 2.1 μmUV Fused Silica
200 nm - 11 μmBarium Fluoride (BaF2)
300 nm - 3 µmInfrasil®
350 nm - 2.0 μmN-BK7
600 nm - 16 µmZinc Selenide (ZnSe)
1.2 - 8 μmSilicon (Si)
2 - 16 μmGermanium (Ge)
Key Specificationsa
Diameter1/2"1"
Thickness3.0 mm5.0 mm
Clear Aperture>90% of Diameter
Surface Flatnessλ/2 over Clear Aperture
Surface Quality40-20 Scratch-Dig
SubstrateSiliconb
  • Please see the Specs tab for detailed specifications.
  • Click Link for Detailed Specifications on the Substrate

Features

  • 1/2" and 1" Diameters Available
  • Ideal for IR Applications in the 1.2 - 8 µm Spectral Range
  • Available Uncoated or AR Coated for <2% Average Reflectance from 3 - 5 µm

Thorlabs' Precision monocrystalline Silicon (Si) Windows are offered in Ø1/2" and Ø1" sizes. They are available uncoated or with an AR coating on both sides that provides <2% average reflectance from 3 - 5 µm (see graphs below). Silicon offers high thermal conductivity and low density, making it suitable for laser windows. However, since silicon has a strong absorption band at 9 µm, it is not suitable for use with CO2 laser transmission applications.

Optic Cleaning Tutorial

Thorlabs also offers precision windows fabricated from several other substrates for use in a large variety of laser and industrial applications. For our complete selection, see the Precision Window Selection Guide table to the right. We also offer laser windows, which have AR coatings centered around commonly used laser wavelengths, and Brewster windows, which are designed to eliminate P-polarized reflected light.

Si Window Transmission
Click to Enlarge

Excel Spreadsheet with Raw Data
This graph shows the measured transmission of an uncoated silicon window at normal incidence.
Antireflective Si Window Transmission
Click to Enlarge

Excel Spreadsheet with Raw Data
This graph shows the measured transmission of an AR-coated silicon window at normal incidence. The shaded region denotes the AR coating range, over which Ravg < 2%.
SpecificationWG80530WG81050WG80530-EWG81050-E
AR Coating RangeUncoated3 - 5 µm
(Ravg < 2% at Normal Incidence)
Diameter1/2"1"1/2"1"
Diameter Tolerance+0.0 / -0.2 mm
Thickness3.0 mm5.0 mm3.0 mm5.0 mm
Thickness Tolerance±0.1 mm±0.3 mm
Clear Aperture>90% of Diameter
Surface Flatness
(at 633 nm)
λ/2 over Clear Aperture
Surface Quality40-20 Scratch-Dig
Parallelism≤2 arcmin<3 arcmin
Damage Threshold-0.25 J/cm2
(3.3 μm, 6 ns, 30 kHz, Ø0.0483 mm)
SubstrateSilicona
  • Click Link for Detailed Specifications on the Substrate
Damage Threshold Specifications
Coating Designation
(Item # Suffix)
Damage Threshold
-E0.25 J/cm2 (3.3 μm, 6 ns, 30 kHz, Ø0.0483 mm)

Damage Threshold Data for Thorlabs' E-Coated Silicon Windows

The specifications to the right are measured data for Thorlabs' E-coated silicon windows. Damage threshold specifications are constant for all E-coated, silicon windows, regardless of the size of the window.

 

Laser Induced Damage Threshold Tutorial

This 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/DIS11254 specifications. A standard 1-on-1 testing regime is performed to test the damage threshold.

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 a set duration of time (CW) or number of pulses (prf 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 LocationsLocations with DamageLocations Without Damage
1.50 J/cm210010
1.75 J/cm210010
2.00 J/cm210010
2.25 J/cm21019
3.00 J/cm21019
5.00 J/cm21091

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 it is only representative of one coating run and that Thorlabs' specified damage thresholds 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. Additionally, when pulse lengths are between 1 ns and 1 µs, LIDT can occur either because of absorption or a dielectric breakdown (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 large 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. Linear power density of your beam (total power divided by 1/e2 spot size)
  3. Beam diameter of your beam (1/e2)
  4. Approximate intensity profile of your beam (e.g., Gaussian)

The power density of your beam should be calculated in terms of W/cm. The graph to the right shows why the linear power density provides the best metric for long pulse and CW sources. Under these conditions, linear power density scales independently of spot size; 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 consider hotspots in the beam or other nonuniform 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). 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 pulse lengths that our specified LIDT values are relevant for.

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 Durationt < 10-9 s10-9 < t < 10-7 s10-7 < t < 10-4 st > 10-4 s
Damage MechanismAvalanche IonizationDielectric BreakdownDielectric Breakdown or ThermalThermal
Relevant Damage SpecificationN/APulsedPulsed and CWCW

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 the energy density provides the best metric for short pulse sources. Under these conditions, energy density scales independently of spot size, 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 power 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 (1997).
[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).

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
WG80530 Support Documentation WG80530 : Ø1/2" Silicon Broadband Precision Window, Uncoated
WG80530-E Support Documentation WG80530-E : Ø1/2" Silicon Broadband Precision Window, AR Coated: 3 - 5 µm
WG81050 Support Documentation WG81050 : Ø1" Silicon Broadband Precision Window, Uncoated
WG81050-E Support Documentation WG81050-E : Ø1" Silicon Broadband Precision Window, AR Coated: 3 - 5 µm

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Posted Comments:
Poster: a.wienke
Posted Date: 2014-04-29 11:23:19.87
Hi, Do you also have any transmission data below 2.0 µm? Down to 1.9 µm would be fine for me.
Poster: jlow
Posted Date: 2014-04-29 05:08:28.0
Response from Jeremy at Thorlabs: I will send you this information directly.
Poster: elharel
Posted Date: 2014-02-11 17:32:46.72
Is this amorphous or crystalline silicon?
Poster: jlow
Posted Date: 2014-02-13 09:01:28.0
Response from Jeremy at Thorlabs: These are monocrystalline Si.
Poster: tcohen
Posted Date: 2012-05-09 16:09:00.0
Update from Tim at Thorlabs: Unfortunately, our standard –C coating is typically used with materials of much lower index and would not yield positive results on a Silicon substrate. I have contacted you to continue this discussion.
Poster: tcohen
Posted Date: 2012-05-09 14:12:00.0
Response from Tim at Thorlabs: Thank you for your feedback! We do have 1550 nm AR coated windows utilizing different substrates. For this substrate, we may be able to offer a special with our standard –C coating. I will contact you to get more information on your application and to continue this conversation.
Poster: goetz
Posted Date: 2012-05-08 11:24:40.0
This product would be useful to me if it were AR coated for 1550 nm.
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Silicon Windows, Uncoated

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Silicon Windows, AR Coated: 3 - 5 µm

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WG81050-E Ø1" Silicon Broadband Precision Window, AR Coated: 3 - 5 µm
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