Mounted Optical Slits

  • 10 Slit Widths Available Ranging from 5 - 200 µm
  • Ø1" Housing is SM1 Compatible


20 µm Slit Width


5 µm Slit Width

This image of an S100RD optical slit was taken with a scanning electron microscope.


150 µm Slit Width

Related Items

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Item # Slit Width Tolerance Pinhole Material Housing Material
S5RD 5 µm ±1 µm 302 Stainless Steel 6061-T6 Aluminum
S10RD 10 µm ±1 µm
S15RD 15 µm ±1.5 µm
S20RD 20 µm ±2 µm
S30RD 30 µm ±2 µm
S40RD 40 µm ±3 µm
S50RD 50 µm ±3 µm 316 Stainless Steel
S100RD 100 µm ±4 µm 302 Stainless Steel
S150RD 150 µm ±4 µm
S200RD 200 µm ±4 µm

Optical Slit Dimensions & Material

  • Slit Widths Available: 5 - 200 µm (See Table to the Right)
  • Slit Length: 3 mm
  • Slit Material: Stainless Steel with Black Oxide Finish
  • Housing: Black-Anodized Aluminum with Ø1" Outer Diameter x 0.10" Thick
  • Unmounted Slit: Ø3/8" (Ø9.5 mm)

These optical slits are mounted in a Ø1" plate, perfect for mounting in our SM1-series lens tubes (SM1L03). The slit in the foil is not necessarily aligned horizontally or vertically relative to the housing during the assembly process.

If you do not see what you need in our stocked offerings below, it is possible to special order slits that are fabricated from different substrate materials, have different slit sizes, incorporate multiple slits in one foil, or provide different slit configurations. Customized housings are also available. Please contact Tech Support to discuss your specific needs.

In order to illustrate the process of determining whether a given laser system will damage an optic, a number of example calculations of laser induced damage threshold are given below. For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. To use the calculator, enter the specified LIDT value of the optic under consideration and the relevant parameters of your laser system in the green boxes. The spreadsheet will then calculate a linear power density for CW and pulsed systems, as well as an energy density value for pulsed systems. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. This calculator assumes a Gaussian beam profile, so a correction factor must be introduced for other beam shapes (uniform, etc.). The LIDT scaling laws are determined from empirical relationships; their accuracy is not guaranteed. Remember that absorption by optics or coatings can significantly reduce LIDT in some spectral regions. These LIDT values are not valid for ultrashort pulses less than one nanosecond in duration.

Intensity Distribution
A Gaussian beam profile has about twice the maximum intensity of a uniform beam profile.

CW Laser Example
Suppose that a CW laser system at 1319 nm produces a 0.5 W Gaussian beam that has a 1/e2 diameter of 10 mm. A naive calculation of the average linear power density of this beam would yield a value of 0.5 W/cm, given by the total power divided by the beam diameter:

CW Wavelength Scaling

However, the maximum power density of a Gaussian beam is about twice the maximum power density of a uniform beam, as shown in the graph to the right. Therefore, a more accurate determination of the maximum linear power density of the system is 1 W/cm.

An AC127-030-C achromatic doublet lens has a specified CW LIDT of 350 W/cm, as tested at 1550 nm. CW damage threshold values typically scale directly with the wavelength of the laser source, so this yields an adjusted LIDT value:

CW Wavelength Scaling

The adjusted LIDT value of 350 W/cm x (1319 nm / 1550 nm) = 298 W/cm is significantly higher than the calculated maximum linear power density of the laser system, so it would be safe to use this doublet lens for this application.

Pulsed Nanosecond Laser Example: Scaling for Different Pulse Durations
Suppose that a pulsed Nd:YAG laser system is frequency tripled to produce a 10 Hz output, consisting of 2 ns output pulses at 355 nm, each with 1 J of energy, in a Gaussian beam with a 1.9 cm beam diameter (1/e2). The average energy density of each pulse is found by dividing the pulse energy by the beam area:

Pulse Energy Density

As described above, the maximum energy density of a Gaussian beam is about twice the average energy density. So, the maximum energy density of this beam is ~0.7 J/cm2.

The energy density of the beam can be compared to the LIDT values of 1 J/cm2 and 3.5 J/cm2 for a BB1-E01 broadband dielectric mirror and an NB1-K08 Nd:YAG laser line mirror, respectively. Both of these LIDT values, while measured at 355 nm, were determined with a 10 ns pulsed laser at 10 Hz. Therefore, an adjustment must be applied for the shorter pulse duration of the system under consideration. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration:

Pulse Length Scaling

This adjustment factor results in LIDT values of 0.45 J/cm2 for the BB1-E01 broadband mirror and 1.6 J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm2 maximum energy density of the beam. While the broadband mirror would likely be damaged by the laser, the more specialized laser line mirror is appropriate for use with this system.

Pulsed Nanosecond Laser Example: Scaling for Different Wavelengths
Suppose that a pulsed laser system emits 10 ns pulses at 2.5 Hz, each with 100 mJ of energy at 1064 nm in a 16 mm diameter beam (1/e2) that must be attenuated with a neutral density filter. For a Gaussian output, these specifications result in a maximum energy density of 0.1 J/cm2. The damage threshold of an NDUV10A Ø25 mm, OD 1.0, reflective neutral density filter is 0.05 J/cm2 for 10 ns pulses at 355 nm, while the damage threshold of the similar NE10A absorptive filter is 10 J/cm2 for 10 ns pulses at 532 nm. As described on the previous tab, the LIDT value of an optic scales with the square root of the wavelength in the nanosecond pulse regime:

Pulse Wavelength Scaling

This scaling gives adjusted LIDT values of 0.08 J/cm2 for the reflective filter and 14 J/cm2 for the absorptive filter. In this case, the absorptive filter is the best choice in order to avoid optical damage.

Pulsed Microsecond Laser Example
Consider a laser system that produces 1 µs pulses, each containing 150 µJ of energy at a repetition rate of 50 kHz, resulting in a relatively high duty cycle of 5%. This system falls somewhere between the regimes of CW and pulsed laser induced damage, and could potentially damage an optic by mechanisms associated with either regime. As a result, both CW and pulsed LIDT values must be compared to the properties of the laser system to ensure safe operation.

If this relatively long-pulse laser emits a Gaussian 12.7 mm diameter beam (1/e2) at 980 nm, then the resulting output has a linear power density of 5.9 W/cm and an energy density of 1.2 x 10-4 J/cm2 per pulse. This can be compared to the LIDT values for a WPQ10E-980 polymer zero-order quarter-wave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm2 for a 10 ns pulse at 810 nm. As before, the CW LIDT of the optic scales linearly with the laser wavelength, resulting in an adjusted CW value of 6 W/cm at 980 nm. On the other hand, the pulsed LIDT scales with the square root of the laser wavelength and the square root of the pulse duration, resulting in an adjusted value of 55 J/cm2 for a 1 µs pulse at 980 nm. The pulsed LIDT of the optic is significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. However, the large average linear power density of the laser system may cause thermal damage to the optic, much like a high-power CW beam.

Posted Comments:
Francesco Leone  (posted 2020-08-07 03:38:37.0)
Hi I'd like to know if your slits can be used in vacuum or if you have and hoc product. Thanks Francesco
nbayconich  (posted 2020-08-07 02:39:53.0)
Thank you for contacting Thorlabs. These slits are not vacuum compatible, I will reach out to you directly to discuss other alternatives.
user  (posted 2019-08-15 01:55:38.38)
I read in the comments that you can provide slits longer than your standard 3mm; could you make a custom slit 13mm long, with a 5um opening? And 16mm long with the same 5um opening? How straight can the line be? All would be mounted in an SM1 tube. How much would it cost?
YLohia  (posted 2019-08-15 10:48:03.0)
Hello, thank you for contacting Thorlabs. Custom items can be requested by emailing us at We will reach out to you directly to discuss the possibility of offering this.
taeshinkim0426  (posted 2017-08-25 10:29:49.053)
Hi, I'm interested in the double slit and triple slit. 50 µm slits: 150 µm Spacing (Center to Center) Please contact me. thanks.
nbayconich  (posted 2017-08-29 08:04:35.0)
Thank you for contacting Thorlabs. I will reach out to you directly with a quote.
chiwon.lee  (posted 2017-05-24 20:38:06.847)
Hi, I need an unmounted 5 um wide slit made of just stainless steel without oxide, to make it conductive. Please contact me. Thanks
nbayconich  (posted 2017-06-06 09:06:51.0)
Thank you for contacting Thorlabs. We can provide a 5 µm slit without the black oxide finish. A Techsupport representative will contact you directly with more information.  (posted 2016-11-22 10:44:13.87)
To be able to decide if we can use the S150R I need to know more on the black oxide coating of the part. Specifically what is the type of black oxide used ? is it copper based (low Temperature blacking process) or high T Feoxide process. Could you sent additional info perhaps please ? Thank you .
tfrisch  (posted 2016-11-29 04:17:52.0)
Hello, I will contact you directly about the black oxide process.
thomas.hutterer  (posted 2014-06-11 14:34:16.987)
Hi, I would like to know if I could buy a slit without the mount, And if not, if it is possible to get the slit out of the mount by myself Regards Thomas Hutterer
jlow  (posted 2014-06-11 10:36:32.0)
Response from Jeremy at Thorlabs: We can provide these slits unmounted. You can also take the slit out of the mount easily by using a good pair of tweezers and carefully pulling out the split end retaining ring.
cdaly  (posted 2012-12-05 17:44:00.0)
Response from Chris at Thorlabs: Thank you for using our feedback. In this case, the slit you need would be a custom item, but one that I believe we can quote for you. I will contact you directly to discuss this further.
eric  (posted 2012-12-05 23:39:44.82)
I'm interested in getting 50 µm vertical slit that is unmounted and does not have the black oxide coating. Could you let me know if it is possible to get this custom part, and if so send me a quote? Thank you.
jlow  (posted 2012-11-12 17:05:00.0)
Response from Jeremy at Thorlabs: We could supply the mounted slits and pinholes with Ø1/2" outer diameter as a custom. I will get in contact with you directly regarding this.
acable  (posted 2012-11-08 14:17:43.457)
Is it possible to get these in a 1/2" diameter mount.
tcohen  (posted 2012-06-12 14:10:00.0)
Response from Tim at Thorlabs to Karsten: Thank you for contacting us! Although the housing is 1” diameter, the diameter of the standard unmounted slit is 9.5mm. To accommodate your 13mm requirement we will need to discuss your desired specifications. I will contact you directly to continue this conversation.
karsten.sperlich  (posted 2012-06-12 11:00:24.0)
Dear Thorlabs team, I need a 13 µm slit which is 14 mm tall. The S15R with 15 µm would be OK, but the height needs to be at least 13 mm. Furthermore I could use 20 µm, 25 µm and 30 µm. Each at least 13 mm long. If that is possible please send me a quote for these slits. Thanks in advance and best regards, Karsten
tcohen  (posted 2012-04-03 12:23:00.0)
Response from Tim at Thorlabs: We should be able to provide this custom slit for you. I have contacted you directly to get more information.
Simone.Rupp  (posted 2012-04-03 10:29:28.0)
Dear Thorlabs team, is it possible to get a 50µm or 100µm slit that is 6mm tall (instead of the offered 3mm)? If yes, could you contact me with a quote? Thanks!
jjurado  (posted 2011-08-29 09:28:00.0)
Response from Javier at Thorlabs to rmartin: Thank you very much for your feedback! We will review the design of our vertical slits and will let you know if we add this change.
rmartin  (posted 2011-08-22 13:56:50.0)
I have used your fixed vertical slits for spectroscopy and thought after many hours of assembly that if your slit discs had a small hole or dimple (on either side) on the aluminum substrate just inside the area taken up by the retaining ring it would make adjusting it to the opto-mechanical axes (vertical or horizontal) far easier. It would also allow the slit to be held in place while the retaining ring was tightened. Just a suggestion.
apalmentieri  (posted 2010-03-25 11:01:37.0)
A response from Adam at Thorlabs to Vitali: We can offer this quotation. I will contact you directly with a quote and instructions for ordering from South Korea.
yahtoug  (posted 2010-03-25 10:20:25.0)
Please, send me quotation for the customized versions: Two pieces of S100R modified to housing Ø 0.5". Two pieces of S150R modified to housing Ø 0.5". Please, advise how to order from South Korea. Thank you. Vitali.
yahtoug  (posted 2010-03-25 10:07:08.0)
Please, send me quotation for the customized versions: Two pieces of S100R modified to Ø 0.5". Two pieces of S150R also modified to Ø 0.5". Please, advise how to order from South Korea. A lot of thanks. Vitali.
jens  (posted 2010-02-11 17:41:59.0)
A reply from Jens at Thorlabs: yes, we can offer custom versions including unmounted versions. I will contact you regarding the details required for the quote.
wikszak  (posted 2010-02-11 17:07:05.0)
Is it possible to get umounted slits ? That would fit with the diameter of my application... Thanks !
james.harrison  (posted 2008-07-04 08:28:33.0)
Dear Sir/Madame I need to be able to mount an S125R within a 0.5" diameter lens tube, as I have very limited space requirements. Would it be possible to provide me just with the aperature disk to perhaps allow me to mount it within an LMR adapter? Many thanks, James
technicalmarketing  (posted 2007-12-27 12:29:00.0)
Thank you for pointing out that the specifications for the slits needed clarification. This has been done.
acable  (posted 2007-12-21 12:06:42.0)
Please indicate the slit hieght and clean up what you mean by diameter. It is given as 3/8" and 1", just need to note mounted versus unmounted.

Mounted Optical Slits

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
S5RD Support Documentation
S5RDØ1" Mounted Slit, 5 ± 1 µm Wide, 3 mm Long
S10RD Support Documentation
S10RDØ1" Mounted Slit, 10 ± 1 µm Wide, 3 mm Long
S15RD Support Documentation
S15RDØ1" Mounted Slit, 15 ± 1.5 µm Wide, 3 mm Long
S20RD Support Documentation
S20RDØ1" Mounted Slit, 20 ± 2 µm Wide, 3 mm Long
S30RD Support Documentation
S30RDØ1" Mounted Slit, 30 ± 2 µm Wide, 3 mm Long
S40RD Support Documentation
S40RDØ1" Mounted Slit, 40 ± 3 µm Wide, 3 mm Long
S50RD Support Documentation
S50RDØ1" Mounted Slit, 50 ± 3 µm Wide, 3 mm Long
S100RD Support Documentation
S100RDØ1" Mounted Slit, 100 ± 4 µm Wide, 3 mm Long
S150RD Support Documentation
S150RDØ1" Mounted Slit, 150 ± 4 µm Wide, 3 mm Long
S200RD Support Documentation
S200RDØ1" Mounted Slit, 200 ± 4 µm Wide, 3 mm Long
5-8 Days