LWIR Achromatic Doublets Optimized for 8 - 12 µm

  • AR Coating for 8 - 12 µm
  • Design Wavelengths at 8 µm, 10 µm, and 12 µm
  • 1" Outer Diameter


f = 75 mm


f = 50 mm

Each mount includes an engraved arrow
indicating the direction of light propagation
required to collimate a point source.

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General Specifications
Diameter Ø1" (Ø25.4 mm)
Dimension Tolerance +0.00/-0.10
Centration <3 arcmin
Clear Aperture Ø20 mm
Spot Size Diffraction Limited On Axis
Design Wavelengths 8 µm, 10 µm, and 12 µm
Antireflection Coating Ravg < 1.5% from 8 to 12 µm, 0° AOI
Substrates Zinc Selenideand Zinc Sulfide
Focal Length Tolerance ±1% at 10 µm
RMS WFE <λ/10 @ 10 µm
Surface Quality 60-40 Scratch-Dig
  • Click Link for Detailed Specifications on the Substrate


  • Air-Spaced Doublet Design Provides Superior Aberration Performance than Singlet Lenses
  • AR Coated for the 8 - 12 µm Range
  • Designs Incorporate Zinc Selenide (ZnSe) and Zinc Sulfide (ZnS) Substrates
  • Engraved Ø1" Mount for SM1 Compatiblity

These AR-coated, air-spaced achromatic doublet lenses provide excellent transmission in the 8 - 12 µm range (surface reflectance for each coating can be seen in the graph to the right). They incorporate two AR-coated lenses, one with a zinc selenide substrate and another with a zinc sulfide substrate. Each achromatic doublet on this page has three design wavelengths: 8 µm, 10 µm, and 12 µm. By optimizing the design for these three wavelengths, the focal shift across the 8 - 12 µm range will be minimized (see the graphs below for details), providing excellent on-axis performance.

Thorlabs' LWIR achromatic doublets are pre-mounted in engraved Ø1" outer diameter mounts, making it easy to incorporate these optics into your setup. Each engraving includes the part number, AR coating range, focal length, an arrow indicating the direction of light propagation to collimate a point source, and an infinity symbol denoting that this lens has an infinite conjugate ratio (i.e., if a diverging light source is placed one focal length away from the flat side of the lens, the light rays emerging from the curved side will be collimated).

Note: We do not recommend disassembly of these lenses, as this may affect performance.

Optic Cleaning Tutorial
Optical Coatings and Substrates
Zemax Files
Click on the red Document icon next to the item numbers below to access the Zemax file download.
Note: The optical coating on these lenses contains thorium tetrafluoride (ThF4) due to its superior performance in the IR. This is a radioactive material, and thus, these lenses should be handled with care. Additionally, ZnSe is a hazardous material. For your safety, please follow all proper precautions while handling any ZnSe products, including wearing gloves and thoroughly washing your hands afterward.

Posted Comments:
bdada  (posted 2011-12-20 17:37:00.0)
Response from Buki at Thorlabs: We expect the air spaced doublets to handle up to a linear power density of 35kW/cm. Please contact TechSupport@thorlabs.com if you have any questions.
manuel.uphoff  (posted 2011-12-12 06:26:00.0)
What is the damage threshold of these lenses for a cw CO2-Laser?
jjurado  (posted 2011-08-01 09:24:00.0)
Response from Javier at Thorlabs to nick: Thank you for contacting us. We will send you this information shortly.
nick  (posted 2011-07-25 08:35:22.0)
Can you please provide me with the optical prescription of this lens (radius, aspheric / conic terms, thickness, seperation distance)? Thank you in advance! Nick

8 - 12 µm Air-Spaced Achromatic Doublets

Item # f
Left Lens
Right Lens
AC254-050-F 50 15.0 37.2 Air-Spaced Doublet Drawing Plot Zinc Selenide Zinc Sulfide
AC254-075-F 75 12.1 65.1
AC254-100-F 100 11.5 90.5
AC254-200-F 200 10.0 194.3
  • "Left" and "Right" refer to the orientations of the lenses in the drawing found in the Reference Drawing column.
  • Click on for plots and downloadable data of the focal length shift and transmission for the lens.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
AC254-050-F Support Documentation
AC254-050-FZnSe-ZnS Air-Spaced Achromatic Doublet, ARC: 8-12 µm, f=50 mm
Lead Time
AC254-075-F Support Documentation
AC254-075-FZnSe-ZnS Air-Spaced Achromatic Doublet, ARC: 8-12 µm, f=75 mm
AC254-100-F Support Documentation
AC254-100-FZnSe-ZnS Air-Spaced Achromatic Doublet, ARC: 8-12 µm, f=100 mm
5-8 Days
AC254-200-F Support Documentation
AC254-200-FZnSe-ZnS Air-Spaced Achromatic Doublet, ARC: 8-12 µm, f=200 mm