NIR Air-Spaced Achromatic Doublets, AR Coated: 650 - 1050 nm

  • Minimal Focal Shift Over the Design Wavelength Range
  • Superior Performance When Compared to Cemented Doublets
  • 1" Outer Diameter Aluminum Housing



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

Related Items

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Coating Range 650 - 1050 nm
Design Wavelengths 706.5, 855, 1015 nm
Surface Quality 20-10 Scratch-Dig
(to Prevent Scattering from
High Power Sources)
Clear Aperture Ø20 mm
Irregularity per Surface <λ/4 at 633 nm
Focal Length Tolerance ±1% at 855 nm
Reflectance Ravg < 0.5% (650-1050 nm)
Housing Ø1" 6061-T6 Aluminum Barrel
Air-Spaced Doublet in a Lens Tube
Click to Enlarge

Air-Spaced Achromatic Doublet in an SM1L30C Slotted Lens Tube with Two SM1RR Retaining Rings


  • Air-Spaced Doublet Design Provides Superior Aberration Performance than Singlet Lenses
  • Ø20 mm Clear Aperture
  • 1" Outer Diameter for Mounting Inside a Ø1" Lens Tube
  • AR Coating for the 650 - 1050 nm Range

Thorlabs' Air-Spaced Achromatic Doublets are designed to provide superior spherical and chromatic aberration correction. Air-Spaced Doublets have two more degrees of freedom than cemented doublets because the interior lens surfaces do not need to have the same curvature. These extra variables allow the performance of these air-spaced doublets to exceed the performance of equivalent cemented doublets in some cases. For details, please see the Lens Comparison tab. The air-spaced design is also highly resistant to laser damage, since no cement is utilized in the fabrication process. They are designed for excellent performance across the 650 - 1050 nm range.

The doublets are pre-mounted in an aluminum barrel with tight tolerances on lens and barrel diameter to minimize the effects of lens decentering. Each mount includes an engraving with the part number, AR coating wavelength, focal length, and the direction of light propagation required to collimate a point source. The mount has a 1" outer diameter for mounting inside a Ø1" lens tube (as shown in the photo to the right).

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.

The table below contains links to pop-ups with plots containing a comparison of the theoretical performance of an air-spaced achromatic doublet and a cemented achromatic doublet with the same focal length. Comparisons are made for the transmitted wavefront error and spot radius. Raw data from each graph below can be downloaded by clicking here.

650 - 1050 nm Lenses

Cemented Item #a Air-Spaced Item #a Wavefront Error Plots Spot Diameter Plots
AC254-030-B ACA254-030-B 30 mm WFE 30 mm Spot Radius
AC254-050-B ACA254-050-B 50 mm WFE 50 mm Spot Radius
AC254-060-B ACA254-060-B 60 mm WFE 60 mm Spot Radius
AC254-075-B ACA254-075-B 75 mm WFE 75 mm Spot Radius
AC254-100-B ACA254-100-B 100 mm WFE 100 mm Spot Radius
AC254-150-B ACA254-150-B 150 mm WFE 150 mm Spot Radius
AC254-200-B ACA254-200-B 200 mm WFE 200 mm Spot Radius
  • For the f = 30 mm lenses, the clear aperture was measured with a Ø11 mm aperture. All other lenses were measured over the entire clear aperture.
Plot Key
Cemented Doublets Air Spaced
Air-Spaced Doublets Cemented Key
Diffraction Limit
Airy Disk

Posted Comments:
Tomer Cohen  (posted 2020-05-24 13:36:02.033)
Hello, Please provide external dimensions tolerances of the Doublet, i would like to implement the lens in my system and tolerance value is ambiguous. Thanks in advance
YLohia  (posted 2020-06-02 01:18:36.0)
Hello, thank you for contacting Thorlabs. Are you requesting the outer diameter tolerances for the housing or the actual lenses themselves? If it's the latter, please note that we do not recommend disassembling the lens from the housing as that can affect the performance. I have reached out to you directly to clarify these points.
kz  (posted 2018-09-21 10:23:46.773)
I am planning to use the ACA254-050-B doublet with pulsed IR laser, pulse length is 33 ns and laser power is 20 W (pulse energy is 0.64 mJ). I was wondering if the doublet I am planning to use can withstand such laser power? I did not find any information about LIDT for the doublet. Please, verify for me that this doublet can be used. Best regards, Kirill Zhuravlev
nbayconich  (posted 2018-09-28 01:44:09.0)
Thank you for contacting Thorlabs. We have not performed LIDT tests on these items. We will need to know more information about your source such as the beam diameter, and wavelength to determine if the pulsed energy density is suitable for these lenses. I will reach out to you directly to discuss your application.
Xiaomin.Nie  (posted 2017-04-10 00:14:31.313)
when I download zemax file of ACA254-030-B and check chromatic focus shift, I found very large shifts (-94um@0.7um and 84um@1um). Should I do something instead of opening and file and checking chromatic focus shift directly? Could you please explain a little bit?
tfrisch  (posted 2017-04-27 01:55:32.0)
Hello, thank you for contacting Thorlabs. I see you are already communicating with a member of our Tech Support Team about this focal shift. We can continue the discussion by email.
barry.luther-davies  (posted 2017-03-14 19:31:00.173)
Is there a reason why you do not offer air spaced achromatic doublets with c-coating for 1050-1700nm?
tfrisch  (posted 2017-03-15 08:51:17.0)
Hello, thank you for contacting Thorlabs. We have been able to offer air spaced achromats for 1050-1700nm in the past, so I will reach out to you directly about your requirements.
chad.e.ogden  (posted 2014-09-24 18:24:53.56)
I purchased 3 of the ACA254-100-B doublets in January 2014. I found that the optical axis of the doublet was far off enough from the mechanical axis of the cell that when I built a small telescope with them in an SM1 lens tube, it had severe coma, even after centering the lens cell with 3 shims. I disassembled the doublets and inspected the fit tolerances, to see if I could shim the optics within the cells to improve the alignment of the optical axis to the cell. The fit was tight enough that I could not slide a 1 mil shim in the gap, but the upper lens did have a little bit of wiggle room. When I carefully reassembled the doublet, I found that almost all of the coma had vanished. I hypothesize that perhaps the cell was assembled without the proper care. If it was held at an angle while tightening the retaining ring, the twp optics could seat slightly off-center. I found that by carefully disassembling each cell and reassembling it, I was able to dramatically reduce the coma in each case. I also noticed that the spacer ring between the two optics has a bevel on one side only, only noticeable under magnification. Doubtless this is intended to seat inside the concave optic. Due to the small size of this bevel, it would be very easy for the assembler to install the ring upside-down without noticing, which could prevent the optics from auto-centering as the retaining ring is tightened. I recommend that you check your assembly process, because the doublets I received were not performing to the design parameters due most likely to erroneous assembly.
jlow  (posted 2014-10-02 03:07:12.0)
Response from Jeremy at Thorlabs: Thank you very much for the detailed feedback about the air-spaced doublets. As you had mentioned in your feedback, the tolerance of the lenses to the inner diameter of the housing are held pretty tightly. This was done in order to limit the amount aberrations in the system. Obviously this is not enough and a good alignment process is required. As a result from your feedback, we have identified some areas to improve our assembly process and we will be testing these during production in an interferometric setup to verify good alignment.
clarafly  (posted 2014-01-03 13:29:02.59)
Why don't you offer -C version of these air-spaced doublets?
tcohen  (posted 2014-01-03 12:20:31.0)
Response from Tim at Thorlabs: Our production team is constantly engaged in new product designs and so we choose the most popular versions to release first. As we receive feedback and see demand, we continue to fill out the line. Thanks for taking the time to post your inquiry. As a large part of our catalog is shaped by our customers' feedback, we appreciate these inquiries to keep us continually moving towards manufacturing what our customers need.
tvandersar  (posted 2013-12-02 21:35:58.59)
I think it is very strange that, according to your graphs, all 2.54cm diameter air-spaced achromatic doublets (except the 200mm) actually have larger focal shift than the cemented achromatic doublets. Could you please comment?
tcohen  (posted 2014-01-03 12:19:25.0)
Response from Thorlabs: The Air-Spaced Achromatic Doublets were designed to provide diffraction limited performance at discrete wavelengths for high powered applications. The slightly higher focal shift is a by-product of the design. However, we are currently working on new air-spaced designs to provide the same optical performance while maintaining or reducing the focal shift.
user  (posted 2013-10-27 17:14:01.063)
In terms of focusing a laser beam, what is the difference between the Air-Spaced Doublets and the Aspheric Lenses? Thank you
tcohen  (posted 2013-10-29 13:12:00.0)
Response from Tim at Thorlabs: Thank you for contacting us. The Air-Spaced Doublets are achromatic, so they provide diffraction limited performance for more broadband sources than an aspheric lens would, which is only corrected for spherical aberrations. Your actual spot size will depend on your wavelength spread, diameter and incoming collimation quality so to provide further details it would be best to discuss it particular to your source. I don’t see that you left any contact info, so to discuss this further, please contact us at
zczeng  (posted 2013-06-05 13:49:51.133)
with the lens comparasion information, the scale bar of the Aberration Information is not the same. and for A coating, the lens with small focal length have big focus spot than long focal length, please check it.
sharrell  (posted 2013-06-17 15:24:00.0)
Response from Sean at Thorlabs: Thank you for your feedback. After internal discussion, we have decided to remove the aberration plots from our website, as they seemed to have caused more confusion than they have helped our customers understand the optic performance. Our decision is supported by the fact that spherical aberration is practically the sole contributor to the error in these systems. Spherical aberration is manifested and better communicated in both the spot size and wavefront error plots that we are continuing to provide. For your second question, as the NA of the lens increases, it becomes more difficult to manage spherical aberration. This leads to larger spot sizes for lenses with shorter focal lengths. In reviewing your feedback, we also noticed that the sopt size and wavefront error plots had been plotted with the lens refocused at each wavelength; we are working on getting these plots updated with the lens held at a static location and I will update this post when those plots are available.
jlow  (posted 2012-09-26 13:17:00.0)
Response from Jeremy at Thorlabs: These thermally conductive tape are also electrically conductive.
luolcc  (posted 2012-09-26 12:10:59.0)
Is it okay to apply on conductor? i.e. is the tape insulating on the surface?
Thorlabs  (posted 2010-11-29 09:34:47.0)
Response from Javier at Thorlabs to tmpest1: the operating temperature range of the TCDT1 and TCDT2 double-sided tape is -30 to 125 degrees Celsius.
tmpest1  (posted 2010-11-29 01:30:07.0)
Tyler@Thorlabs "Unfortunately we dont know the working temperature range of this thermal tape" Do you have temperature ratings for this double-sided tape since that was written 2 years ago? I just require "normal" temperatures 0-130C.
Tyler  (posted 2008-11-05 16:09:05.0)
A response from Tyler at Thorlabs to denisel: Unfortunately we dont know the working temperature range of this thermal tape. However, we will send you a sample to test in your setup. If you dont mind, please post your findings about how this thermal tape performed in your cryostat.
denisel  (posted 2008-11-04 02:47:50.0)
Would like to find out ratings of this tape at low temperatures? Does it still maintain holding and thermal conductivity say at 77K?
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650 - 1050 nm Air-Spaced Achromatic Doublets

Item # f
Air Gapc
ACA254-030-B 30 19.98 -26.89 -20.19 -37.31 7.79 9.26 1.24 19.5 20.2 Air-Spaced Doublet Drawing
ACA254-050-B 50 24.87 -31.87 -29.52 -271.16 6.64 10.97 0.64 20.9 36.4
ACA254-060-B 60 32.59 -32.59 -29.88 -140.76 6.10 10.97 1.15 21.4 47.4
ACA254-075-B 75 40.81 -40.81 -38.51 -197.03 7.00 10.14 1.08 22.2 62.0
ACA254-100-B 100 49.75 -49.75 -48.68 -135.69 7.00 9.98 1.02 21.8 89.1
ACA254-150-B 150 75.14 -75.14 -75.10 -213.62 7.15 9.85 1.00 22.5 139.0
ACA254-200-B 200 100.82 -100.82 -101.98 -292.29 7.05 9.96 0.99 22.8 189.1
  • Left lens center thickness in the reference drawing.
  • Right lens center thickness in the reference drawing.
  • Center air spacing between the lenses.
Item # Transmission Plotd Left Lens Materiale Right Lens Materiale Image Space NA Design RMS
Wavefront Error
ACA254-030-B Plot N-SSK2 N-SF57 0.334 <2λ
ACA254-050-B Plot N-SSK2 N-SF57 0.204 <λ/8
ACA254-060-B Plot N-SSK2 N-SF57 0.167 <λ/8
ACA254-075-B Plot N-SSK2 N-SF57 0.134 <λ/10
ACA254-100-B Plot N-K5 N-SF57 0.100 <λ/15
ACA254-150-B Plot N-K5 N-SF57 0.067 <λ/20
ACA254-200-B Plot N-K5 N-SF57 0.050 <λ/20

d. The shaded region represents the specified coating range of the lenses.
e. "Left" and "Right" refer to the orientations of the lenses in the Reference Drawing found by clicking on the Info Icon above.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ACA254-030-B Support Documentation
ACA254-030-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f=30 mm
ACA254-050-B Support Documentation
ACA254-050-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 50 mm
ACA254-060-B Support Documentation
ACA254-060-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 60 mm
ACA254-075-B Support Documentation
ACA254-075-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 75 mm
Lead Time
ACA254-100-B Support Documentation
ACA254-100-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 100 mm
ACA254-150-B Support Documentation
ACA254-150-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 150 mm
ACA254-200-B Support Documentation
ACA254-200-BAir-Spaced Achromatic Doublet, AR Coating: 650 - 1050 nm, f = 200 mm