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Calcium Fluoride Plano-Convex Lenses, AR Coated: 1.8 - 2.4 µm


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Calcium Fluoride Plano-Convex Lenses, AR Coated: 1.8 - 2.4 µm

Common Specifications
Substrate MaterialVacuum-Grade Calcium Fluoride
AR Coating Range1.8 - 2.4 µm
Reflectance Over
Coating Range (Avg.)
<0.50%
Damage Threshold2 J/cm²
(2.05 µm, 10 ns, 10 Hz, Ø0.186 mm)
Diameters Available1/2" or 1"
Diameter Tolerance+0.00/-0.10 mm
Thickness Tolerance±0.1 mm
Focal Length Tolerance±1%
Surface Quality40-20 Scratch-Dig
Surface Flatness (Plano Side)λ/2
Spherical Surface Powera
(Convex Side)
3λ/2
Surface Irregularity (Peak to Valley)λ/2
Centration≤3 arcmin
Clear Aperture>90% of Diameter
Design Wavelength588 nm
  • Much like surface flatness for flat optics, spherical surface power is a measure of the deviation between the surface of the curved optic and a calibrated reference gauge, typically for a 633 nm source, unless otherwise stated. This specification is also commonly referred to as surface fit.
Optical Coatings and Substrates
Optic Cleaning Tutorial

Features

  • Vacuum-Grade Calcium Fluoride Substrate
  • Ø1/2" and Ø1" Versions Available
  • Broadband AR Coatings for 1.8 - 2.4 µm
  • Focal Lengths from 20.0 - 1000.0 mm

Thorlabs' Ø1/2" and Ø1" Calcium Fluoride (CaF2) Plano-Convex Lenses are available with a broadband AR coating optimized for the 1.8 - 2.4 µm spectral range deposited on both surfaces. This coating greatly reduces the surface reflectivity of the substrate, yielding an average transmission in excess of 99% over the entire AR coating range. See the Graphs tab for detailed information.

Thorlabs also offers Uncoated CaF2 Plano-Convex Lenses, which can be used over the range of 0.18 - 8 µm, and E-Coated CaF2 Plano-Convex Lenses which have an AR coating for the 3 - 5 µm range.

CaF2 is commonly used for applications requiring high transmission in the infrared and ultraviolet spectral ranges. The material exhibits a low refractive index, varying from 1.35 to 1.51 within its usage range of 180 nm to 8.0 μm. Calcium fluoride is also fairly chemically inert and offers superior hardness compared to its barium fluoride, magnesium fluoride, and lithium fluoride cousins.

Plano-Convex lenses have a positive focal length and approach best form for infinite and finite conjugate applications. Please click here for details concerning Best Form Lenses. These lenses focus a collimated beam to the back focus and collimate light from a point source. They are designed with minimal spherical aberration and have a focal length which can be calculated using a simplified thick lens equation:

f= R/(n-1),

where n is the index of refraction and R is the radius of curvature of the lens surface.

Usage:
To minimize the introduction of spherical aberrations, light should be bent gradually as it propagates through the lens. Therefore, when using a plano-convex lens to focus a collimated light source, the collimated light should be incident on the curved surface. Similarly, when collimating a point source of light, the diverging light rays should be incident on the planar surface of the lens.

Selection Guide
Other CaF2 Lenses
Plano-ConvexUncoated
D Coated (1.8 - 2.4 µm)
E Coated (3 - 5 µm)
Bi-ConvexUncoated
E Coated (3 - 5 µm)
Plano-ConcaveUncoated
E Coated (3 - 5 µm)
Bi-ConcaveUncoated/AR Coated
Positive MeniscusUncoated
E Coated (3 - 5 µm)
Negative MeniscusUncoated
E Coated (3 - 5 µm)
Other MIR Lenses
Zinc Selenide (0.6 - 16.0 µm)Plano-Convex
Bi-Convex
Plano-Concave
Bi-Concave
Positive Meniscus
Negative Meniscus
Germanium (2.0 - 16.0 µm)Plano-Convex
Silicon (1.2 - 8.0 µm)Plano-Convex
Barium Fluoride (0.2 - 11.0 µm)Plano-Convex
Magnesium Fluoride (200 nm - 6 µm)Plano-Convex

1.8 - 2.4 µm AR Coating Graphs

CaF2 -D Reflectivity

Shown above is a graph of the measured percent reflectivity of the AR coating as a function of wavelength. The average reflectivity in the 1.8 - 2.4 μm range is <0.50%. The blue shading indicates the region for which the AR coating is optimized. Performance outside of the specified range is not guaranteed and varies from lot to lot.
Click Here for an Excel file with this plot data.

CaF2 -D Coated Transmission

Shown above is a graph of the measured transmission of an AR-coated calcium fluoride plano-convex lens. The blue shaded region denotes the 1.8 - 2.4 μm spectral range where the AR coating is optimized. For this wavelength range, the measured transmission is in excess of 99%. Performance outside of the specified range is not guaranteed and varies from lot to lot.
Click Here for an Excel file with this plot data.

Wavelength-Dependent Focal Length Shift

The paraxial focal length of a lens is wavelength dependent. The focal length listed below for a given lens corresponds to the value at the design wavelength (i.e., the focal length at 588 nm). Since CaF2 offers high transmission from 0.18 - 8.0 µm, users may wish to use these lenses at other popular wavelengths. Click on the icons below to view theoretically-calculated focal length shifts for wavelengths within the 0.18 - 8.0 µm range.

The blue shading indicates the region for which the AR coating is optimized. Please see the Graphs tab for more information.

Ø1/2" Plano-Convex Lenses

Item #LA5315-DLA5183-DLA5458-D
Focal Length @ 588 nm20.0 mm50.0 mm80.0 mm
Focal Length Shift
(Click for Details)
Raw Data
(Click to Download)
DataDataData

Ø1" Plano-Convex Lenses

Item #LA5370-DLA5763-DLA5042-DLA5817-DLA5012-DLA5714-DLA5255-DLA5464-DLA5956-DLA5835-D
Focal Length @ 588 nm40.0 mm50.0 mm75.0 mm100.0 mm150.0 mm200.0 mm250.0 mm500.0 mm750.0 mm1000.0 mm
Focal Length Shift
(Click for Details)
Raw Data
(Click to Download)
DataDataDataDataDataDataDataDataDataData
Damage Threshold Specifications
Coating Designation
(Item # Prefix)
Damage Threshold
-D2 J/cm2 (2.05 µm, 10 ns, 10 Hz, Ø0.186 mm)

Damage Threshold Data for Thorlabs' D-Coated CaF2 Lenses

The specifications to the right are measured data for Thorlabs' D-coated CaF2 lenses. Damage threshold specifications are constant for all D-coated CaF2 lenses, regardless of the size or focal length of the lens.

 

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).

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Posted Comments:
Poster: bdada
Posted Date: 2012-02-01 16:34:00.0
Response from Buki at Thorlabs: Thank you for using our feedback forum. We are currently testing this optic for damage threshold data and will post an update when we get the results.
Poster: manfrin
Posted Date: 2012-01-13 08:48:51.0
We do need the threshold damage, max peak power and max average power for AR coating 1.8-2.4um. Thank you
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Ø1/2" CaF2 Plano-Convex Lenses, AR-Coated: 1.8 - 2.4 µm
Item #DiameterFocal LengthRadius of CurvatureCenter ThicknessEdge ThicknessaBack Focal LengthbReference
Drawing
LA5315-D 1/2" (12.7 mm) 20.0 mm 8.7 mm 4.3 mm 1.5 mm 17.0 mm Plano-Convex Lens Drawing
LA5183-D 1/2" (12.7 mm) 50.0 mm 21.7 mm 2.5 mm 1.5 mm 48.3 mm
LA5458-D 1/2" (12.7 mm) 80.0 mm 34.7 mm 2.1 mm 1.5 mm 78.5 mm
  • Edge thickness given before 0.2 mm at 45° typical chamfer.
  • Measured at the design wavelength, 588 nm.

Suggested Fixed Lens Mount: LMR05

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal/Imperial Price Available / Ships
LA5315-D Support Documentation
LA5315-D Ø1/2" CaF2 Plano-Convex Lens, f = 20.0 mm, AR-Coated: 1.8 - 2.4 µm
$130.00
Today
LA5183-D Support Documentation
LA5183-D Ø1/2" CaF2 Plano-Convex Lens, f = 50.0 mm, AR-Coated: 1.8 - 2.4 µm
$130.00
Today
LA5458-D Support Documentation
LA5458-D Ø1/2" CaF2 Plano-Convex Lens, f = 80.0 mm, AR-Coated: 1.8 - 2.4 µm
$120.00
Today
Ø1" CaF2 Plano-Convex Lenses, AR-Coated: 1.8 - 2.4 µm
Item #DiameterFocal LengthRadius of CurvatureCenter ThicknessEdge ThicknessaBack Focal LengthbReference
Drawing
LA5370-D 1" (25.4 mm) 40.0 mm 17.4 mm 7.5 mm 2.0 mm 34.8 mm Plano-Convex Lens Drawing
LA5763-D 1" (25.4 mm) 50.0 mm 21.7 mm 6.1 mm 2.0 mm 45.7 mm
LA5042-D 1" (25.4 mm) 75.0 mm 32.5 mm 4.6 mm 2.0 mm 71.8 mm
LA5817-D 1" (25.4 mm) 100.0 mm 43.4 mm 3.9 mm 2.0 mm 97.3 mm
LA5012-D 1" (25.4 mm) 150.0 mm 65.1 mm 3.3 mm 2.0 mm 147.7 mm
LA5714-D 1" (25.4 mm) 200.0 mm 86.8 mm 2.9 mm 2.0 mm 198.0 mm
LA5255-D 1" (25.4 mm) 250.0 mm 108.5 mm 2.7 mm 2.0 mm 248.1 mm
LA5464-D 1" (25.4 mm) 500.0 mm 216.9 mm 2.4 mm 2.0 mm 498.3 mm
LA5956-D 1" (25.4 mm) 750.0 mm 325.4 mm 2.2 mm 2.0 mm 748.4 mm
LA5835-D 1" (25.4 mm) 1000.0 mm 433.9 mm 2.2 mm 2.0 mm 998.5 mm
  • Edge thickness given before 0.2 mm at 45° typical chamfer.
  • Measured at the design wavelength, 588 nm.

Suggested Fixed Lens Mount: LMR1

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal/Imperial Price Available / Ships
LA5370-D Support Documentation
LA5370-D Ø1" CaF2 Plano-Convex Lens, f = 40.0 mm, AR-Coated: 1.8 - 2.4 µm
$190.00
Lead Time
LA5763-D Support Documentation
LA5763-D Ø1" CaF2 Plano-Convex Lens, f = 50.0 mm, AR-Coated: 1.8 - 2.4 µm
$190.00
Today
LA5042-D Support Documentation
LA5042-D Ø1" CaF2 Plano-Convex Lens, f = 75.0 mm, AR-Coated: 1.8 - 2.4 µm
$190.00
Today
LA5817-D Support Documentation
LA5817-D Ø1" CaF2 Plano-Convex Lens, f = 100.0 mm, AR-Coated: 1.8 - 2.4 µm
$122.00
Today
LA5012-D Support Documentation
LA5012-D Ø1" CaF2 Plano-Convex Lens, f = 150.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
Today
LA5714-D Support Documentation
LA5714-D Ø1" CaF2 Plano-Convex Lens, f = 200.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
Today
LA5255-D Support Documentation
LA5255-D Ø1" CaF2 Plano-Convex Lens, f = 250.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
Today
LA5464-D Support Documentation
LA5464-D Ø1" CaF2 Plano-Convex Lens, f = 500.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
3-5 Days
LA5956-D Support Documentation
LA5956-D Ø1" CaF2 Plano-Convex Lens, f = 750.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
Today
LA5835-D Support Documentation
LA5835-D Ø1" CaF2 Plano-Convex Lens, f = 1000.0 mm, AR-Coated: 1.8 - 2.4 µm
$132.00
Today
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