Zinc Selenide Negative Meniscus Lenses, AR Coated: 8 - 12 µm


  • AR Coating Optimized for the 8 - 12 µm Range
  • Ideal for CO2 Laser Applications Due to Low Absorption Coefficient
  • Decreases the NA of an Optical System

LF7601-F

(Ø1")

LF7185-F

(Ø1/2")

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Specifications
Substrate Material Laser-Grade Zinc Selenidea
AR Coating Range 8 - 12 μm
Reflectance over Coating
Range (Avg.)
<1.5%
Damage Thresholdb 5 J/cm2
(10.6 µm, 100 ns, 1 Hz, Ø0.478 mm)
Diameter Tolerance +0.00/-0.10
Thickness Tolerance ±0.2 mm
Focal Length Tolerance ±1%
Surface Quality 60-40 Scratch-Dig
Spherical Surface Powerc 3λ/2
Spherical Surface Irregularity
(Peak to Valley)
λ/2
Centration ≤3 arcmin
Clear Aperture 80% of Diameter
Design Wavelength 10.6 μm
  • Click Link for Detailed Specifications on the Substrate
  • Limited by the Antireflection Coating
  • 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.

Features

  • ZnSe Substrate
  • Broadband AR Coating for the 8 - 12 μm Range
  • Focal Lengths from -40 mm to -1000 mm Available

Thorlabs' Ø1/2" and Ø1" Zinc Selenide (ZnSe) Negative Meniscus Lenses are available with a broadband AR coating optimized for the 8 µm to 12 μm spectral range deposited on both surfaces. This coating greatly reduces the high surface reflectivity of the substrate, yielding an average transmission in excess of 97% over the entire AR coating range. See the Graphs tab for detailed information.

Negative meniscus (convex-concave) lenses, which are thinner in the middle than at the edges and cause light rays to diverge, are designed to minimize third-order spherical aberration. When used to diverge light, the convex surface should face the beam to minimize spherical aberration. They are often used in conjunction with other lenses to increase the focal length, and therefore decrease the numerical aperture (NA), of an optical assembly. ZnSe lenses are particularly well suited for use with high-power CO2 lasers.

When handling optics, one should always wear gloves. This is especially true when working with zinc selenide, as it is a hazardous material. For your safety, please follow all proper precautions, including wearing gloves when handling these lenses and thoroughly washing your hands afterward. Click here to download a pdf of the MSDS for ZnSe.

Thorlabs will accept all ZnSe lenses back for proper disposal. Please contact Tech Support to make arrangements for this service.

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.
Optic Cleaning Tutorial
Optical Coatings and Substrates
Selection Guide
Zinc Selenide Lenses
Other MIR Lenses
Other Spherical Singlets

Reflectance of BBAR F-CoatingClick to Enlarge
Click for Raw Data
Shown above is a graph of the reflectance of the -F antireflection coating as a function of wavelength. The average reflectance in the 8 - 12 μm range is <1.5%. The blue shaded region indicates the spectral range for which the AR coating is optimized. Please note that the reflectance values stated for wavelengths outside of the AR coating range are provided only for reference and can vary significantly by coating lot.

Total Transmission of ZnSeClick to Enlarge
Click for Raw Data
Shown above is a graph of the measured transmission of an AR-coated ZnSe Bi-Convex lens. The blue shaded region denotes the 8 - 12 μm spectral range where the AR coating is optimized. For this wavelength range, the transmission is in excess of 97%. Please note that the transmission values stated for wavelengths outside of the AR coating range are provided only for reference and can vary significantly by coating lot.

Damage Threshold Specifications
Coating Designation
(Item # Suffix)
Damage Threshold
-F 5 J/cm2 (10.6 µm, 100 ns, 1 Hz, Ø0.478 mm)

Damage Threshold Data for Thorlabs' F-Coated ZnSe Lenses

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

 

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).

CXY1A in 30 mm Cage System
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CXY1A Translation Mount and
SM1 Lens Tube Mounted in a
30 mm Cage System
Threaded Mounting Adapter
Click to Enlarge

Ø1" Optic Mounted in a
ST1XY-S XY Translator

Click to Enlarge

LMR1 Fixed Mount with Ø1" Lens

Click to Enlarge

LM2XY Translating Mount with Ø2" Lens
Recommended Mounting Options for Thorlabs Lenses
Item # Mounts for Ø2 mm to Ø10 mm Optics
Imperial Metric
(Various) Fixed Lens Mounts and Mini-Series Fixed Lens Mounts for Small Optics, Ø5 mm to Ø10 mm
(Various) Small Optic Adapters for Use with Standard Fixed Lens Mounts, Ø2 mm to Ø10 mm
Item # Mounts for Ø1/2" (Ø12.7 mm) Optics
Imperial Metric
LMR05 LMR05/M Fixed Lens Mount for Ø1/2" Optics
MLH05 MLH05/M Mini-Series Fixed Lens Mount for Ø1/2" Optics
LM05XY LM05XY/M Translating Lens Mount for Ø1/2" Optics
SCP05 16 mm Cage System, XY Translation Mount for Ø1/2" Optics
(Various) Ø1/2" Lens Tubes,
Optional SM05RRC Retaining Ring for High-Curvature Lenses (See Below)
Item # Mounts for Ø1" (Ø25.4 mm) Optics
Imperial Metric
LMR1 LMR1/M Fixed Lens Mount for Ø1" Optics
LM1XY LM1XY/M Translating Lens Mount for Ø1" Optics
ST1XY-S ST1XY-S/M Translating Lens Mount with Micrometer Drives (Other Drives Available)
CXY1A 30 mm Cage System, XY Translation Mount for Ø1" Optics
(Various) Ø1" Lens Tubes,
Optional SM1RRC Retaining Ring for High-Curvature Lenses (See Below)
Item # Mount for Ø1.5" Optics
Imperial Metric
LMR1.5 LMR1.5/M Fixed Lens Mount for Ø1.5" Optics
(Various) Ø1.5" Lens Tubes,
Optional SM1.5RR Retaining Ring for Ø1.5" Lens Tubes and Mounts
Item # Mounts for Ø2" (Ø50.8 mm) Optics
Imperial Metric
LMR2 LMR2/M Fixed Lens Mount for Ø2" Optics
LM2XY LM2XY/M Translating Lens Mount for Ø2" Optics
CXY2 60 mm Cage System, XY Translation Mount for Ø2" Optics
(Various) Ø2" Lens Tubes,
Optional SM2RRC Retaining Ring for High-Curvature Lenses (See Below)
Item # Adjustable Optic Mounts
Imperial Metric
LH1 LH1/M Adjustable Mount for Ø0.28" (Ø7.1 mm) to Ø1.80" (Ø45.7 mm) Optics
LH2 LH2/M Adjustable Mount for Ø0.77" (Ø19.6 mm) to Ø2.28" (Ø57.9 mm) Optics
VG100 VG100/M Adjustable Clamp for Ø0.5" (Ø13 mm) to Ø3.5" (Ø89 mm) Optics
SCL03 SCL03/M Self-Centering Mount for Ø0.15" (Ø3.8 mm) to Ø1.77" (Ø45.0 mm) Optics
SCL04 SCL04/M Self-Centering Mount for Ø0.15" (Ø3.8 mm) to Ø3.00" (Ø76.2 mm) Optics
LH160C LH160C/M Adjustable Mount for 60 mm Cage Systems,
Ø0.50" (Ø13 mm) to Ø2.00" (Ø50.8 mm) Optics
SCL60C SCL60C/M Self-Centering Mount for 60 mm Cage Systems,
Ø0.15" (Ø3.8 mm) to Ø1.77" (Ø45.0 mm) Optics

Mounting High-Curvature Optics

Thorlabs' retaining rings are used to secure unmounted optics within lens tubes or optic mounts. These rings are secured in position using a compatible spanner wrench. For flat or low-curvature optics, standard retaining rings manufactured from anodized aluminum are available from Ø5 mm to Ø4". For high-curvature optics, extra-thick retaining rings are available in Ø1/2", Ø1", and Ø2" sizes.

Extra-thick retaining rings offer several features that aid in mounting high-curvature optics such as aspheric lenses, short-focal-length plano-convex lenses, and condenser lenses. As shown in the animation to the right, the guide flange of the spanner wrench will collide with the surface of high-curvature lenses when using a standard retaining ring, potentially scratching the optic. This contact also creates a gap between the spanner wrench and retaining ring, preventing the ring from tightening correctly. Extra-thick retaining rings provide the necessary clearance for the spanner wrench to secure the lens without coming into contact with the optic surface.


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Ø1/2" Negative Meniscus Lenses

Limited Stock Icon

These items will be retired without replacement when stock is depleted. If you require these parts for line production, please contact our OEM Team.

Item # Diameter Focal
Length
Dioptera Radius of
Curvature 1
Radius of
Curvature 2
Center
Thickness
Edge
Thicknessb
Back Focal
Lengthc
Reference
Drawing
LF7185-F 1/2" -40.0 mm -25.0 10.9 mm 7.6 mm 3.0 mm 4.3 mm -33.6 mm Negative Meniscus Lens Drawing

Suggested Fixed Lens Mount: LMR05(/M)

  • Reciprocal of the Focal Length in Meters
  • Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
  • Measured at the Design Wavelength, 10.6 µm
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
LF7185-F Support Documentation
LF7185-FØ1/2" ZnSe Negative Meniscus Lens, f = -40.0 mm, ARC: 8-12 µm
$424.09
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Ø1" Negative Meniscus Lenses

Limited Stock Icon

These items will be retired without replacement when stock is depleted. If you require these parts for line production, please contact our OEM Team.

Item # Diameter Focal
Length
Dioptera Radius of
Curvature 1
Radius of
Curvature 2
Center
Thickness
Edge
Thicknessb
Back Focal
Lengthc
Reference
Drawing
LF7601-Fd 1" -50.0 mm -20.0 23.0 mm 15.6 mm 4.0 mm 6.7 mm -44.9 mm Negative Meniscus Lens Drawing
LF7053-Fd 1" -75.0 mm -13.3 21.0 mm 15.5 mm 4.0 mm 6.3 mm -66.6 mm
LF7321-Fd 1" -200.0 mm -5.0 57.7 mm 45.9 mm 4.0 mm 4.4 mm -191.9 mm
LF7639-Fd 1" -500.0 mm -2.0 146.1 mm 119.0 mm 4.0 mm 4.1 mm -492.0 mm
LF7589-Fd 1" -750.0 mm -1.3 219.6 mm 179.7 mm 4.0 mm 4.1 mm -742.0 mm
LF7573-Fd 1" -1000.0 mm -1.0 293.0 mm 240.5 mm 4.0 mm 4.1 mm -992.0 mm
  • Reciprocal of the Focal Length in Meters
  • Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
  • Measured at the Design Wavelength, 10.6 µm
  • Suggested Fixed Lens Mount: LMR1(/M)
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
LF7601-F Support Documentation
LF7601-FØ1" ZnSe Negative Meniscus Lens, f = -50.0 mm, ARC: 8-12 µm
$612.97
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LF7053-F Support Documentation
LF7053-FØ1" ZnSe Negative Meniscus Lens, f = -75.0 mm, ARC: 8-12 µm
$612.97
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LF7321-F Support Documentation
LF7321-FØ1" ZnSe Negative Meniscus Lens, f = -200.0 mm, ARC: 8-12 µm
$612.97
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LF7639-F Support Documentation
LF7639-FØ1" ZnSe Negative Meniscus Lens, f = -500.0 mm, ARC: 8-12 µm
$612.97
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LF7589-F Support Documentation
LF7589-FØ1"" ZnSe Negative Meniscus Lens, f = -750.0 mm, ARC: 8-12 µm
$612.97
Today
LF7573-F Support Documentation
LF7573-FØ1" ZnSe Negative Meniscus Lens, f = -1000.0 mm, ARC: 8-12 µm
$612.97
Today