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MWIR Achromatic Doublets Optimized for 3 - 5 µm

  • AR Coating for 3 - 5 µm
  • Design Wavelengths at 3 µm, 4 µm, and 5 µm
  • 1" Outer Diameter


f = 100 mm


f = 200 mm

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

Related Items

Common Specifications
DiameterØ1" (Ø25.4 mm)
Dimension Tolerance+0.00/-0.10 mm
Centration<3 arcmin
Clear Aperture Ø20 mm
Spot SizeDiffraction Limited On Axis
Design Wavelengths3 µm, 4 µm, and 5 µm
Antireflection CoatingRavg < 1.5% from 3 to 5 µm, 0° AOI
SubstratesSilicon and Germanium
Focal Length Tolerance±1% at 4 µm
RMS WFE<λ/10 @ 4 µm
Surface Quality60-40 Scratch-Dig


  • Diffraction-Limited On-Axis Performance
  • AR Coated for the 3 - 5 µm Range
  • Designs Incorporate Si and Ge Substrates
  • Mounted in Engraved SM1-Compatible Housings

These AR-coated, air-spaced achromatic doublet lenses provide excellent transmission in the 3 - 5 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 germanium substrate and another with a silicon substrate.

Each achromatic doublet on this page has three design wavelengths: 3 µm, 4 µm, and 5 µm. By optimizing the design for these three wavelengths, the focal shift across the 3 - 5 µm range will be minimized (see Focal Shift tab for details), providing excellent on-axis performance.

Thorlabs' MWIR achromatic doublets are pre-mounted in engraved SM1-compatible 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. Our entire Zemax Catalog is also available.
Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part NumberProduct Description
AC254-050-E Support Documentation AC254-050-E:Si-Ge Achromatic Doublet, 50 mm EFL, ARC: 3-5 µm
AC254-075-E Support Documentation AC254-075-E:Si-Ge Achromatic Doublet, 75 mm EFL, ARC: 3-5 µm
AC254-100-E Support Documentation AC254-100-E:Si-Ge Achromatic Doublet, 100 mm EFL, ARC: 3-5 µm
AC254-200-E Support Documentation AC254-200-E:Si-Ge Achromatic Doublet, 200 mm EFL, ARC: 3-5 µm

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3 - 5 µm Air-Spaced Achromatic Doublets

Item #f
Reflectance PlotLeft Lens MaterialaRight Lens MaterialaGraphsb
AC254-050-E5010.040.4Air-Spaced Doublet DrawingPlotSiliconGermanium
  • "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/Imperial Price Available / Ships
AC254-050-E Support Documentation
AC254-050-ESi-Ge Achromatic Doublet, 50 mm EFL, ARC: 3-5 µm
AC254-075-E Support Documentation
AC254-075-ESi-Ge Achromatic Doublet, 75 mm EFL, ARC: 3-5 µm
AC254-100-E Support Documentation
AC254-100-ESi-Ge Achromatic Doublet, 100 mm EFL, ARC: 3-5 µm
AC254-200-E Support Documentation
AC254-200-ESi-Ge Achromatic Doublet, 200 mm EFL, ARC: 3-5 µm
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