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Mounted N-BK7 Reflective Neutral Density Filters


  • Optical Densities from 0.1 to 4.0
  • N-BK7 Substrate with Inconel Coating
  • Mounts Engraved with Optical Density

ND01A

Ø25 mm Filter in
SM1-Threaded Mount

ND510A

Ø1/2" Filter in
SM05-Threaded Mount

ND10A

Ø25 mm Filter in 
SM1-Threaded Mount

ND2R40A

Ø2" Filter in
SM2-Threaded Mount

NDK01

Kit Containing 10 Ø25 mm ND Filters (Not to Scale)

Related Items


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Selection Guide for Neutral Density Filters
Absorptive
Uncoated (400 - 650 nm) Mounted
Unmounted
Uncoated (800 - 2600 nm) Mounted
Unmounted
AR-Coated (350 - 700 nm) Mounted
Unmounted
AR-Coated (650 - 1050 nm) Mounted
Unmounted
AR-Coated (1050 - 1700 nm) Mounted
Unmounted
Reflective
N-BK7 (350 - 1100 nm) Mounted
Unmounted
UV Fused Silica (200 - 1200 nm) Mounted
Unmounted
ZnSe (2 - 16 µm) Mounted
Unmounted
Wedged Reflective
Variable Reflective
Neutral Density Filter Kits
Optic Cleaning Tutorial


Click to Enlarge

ND06A ND Filter in
an SM1L20 Lens Tube

Features

  • Ø1/2" (12.7 mm) Filters in SM05-Threaded Cells
  • Ø25 mm Filters in SM1-Threaded Cells
  • Ø50 mm Filters in SM2-Threaded Cells
  • Mount is Engraved with Item Number and Optical Density
  • Attenuation in the Visible and NIR Spectral Regions (See Graphs Tab)
  • Optical Densities Ranging from 0.1 to 4.0

Thorlabs' Mounted N-BK7 Reflective (Metallic) Ø1/2", Ø25, and Ø50 mm Neutral Density (ND) Filters provide uniform attenuation over the broad spectral range from 350 nm to 1100 nm. These filters have optical densities ranging from 0.1 to 4.0; refer to the Specs tab above for detailed information about the average transmission obtained with each of our reflective neutral density filters. The Graphs tab contains plots of the transmission and reflection for each filter for a broad wavelength range. All of our mounted filters are housed in an SM-threaded housing for compatibility with our lens tube systems. For more information on the specifications of the housing's threads, see the Threading Specs tab. 

These filters consist of a N-BK7 glass substrate with a metal (Inconel) coating. Inconel is a metallic alloy that ensures flat spectral response from the UV to the near IR. Unprotected metal coatings like this should only be cleaned by blown air, never touched, as contact may cause scratching to the unprotected surface. Although these are reflective ND filters, the Inconel coating does absorb some of the incident light, which limits the use of these filters to low-power applications. Inconel is resistant to aging under normal conditions; however, it will oxidize at elevated temperatures. To prevent oxidation, Thorlabs recommends using these ND filters at temperatures below 100 °C. To achieve the best performance, light should be incident on the side with the Inconel coating.

We offer a variety of robust storage boxes designed to hold 25 mm and 50 mm mounted filters, which can be found at the bottom of this page. 

These filters are also available unmounted. Other reflective ND filters in Thorlabs' offering include UV fused silica filters and variable ND filters, as well as a complete line of absorptive ND filters in several sizes; the table to the right contains links to all of the available options.

Please note that Thorlabs' Neutral Density Filters are not designed as laser safety equipment. For lab safety, Thorlabs offers an extensive line of safety and blackout products, including beam blocks, that significantly reduce exposure to the stray or reflected light

General Specifications
Filter ND5xxA NDxxA ND2RxxA
Substrate N-BK7a
Diameter
(Unmounted)
12.7 mm 25.0 mm 50.0 mm
Diameter Tolerance
(Unmounted)
+0.0 / -0.25 mm +0.0 / -0.5 mm +0.0 / -0.20 mm
Mountb SM05-Threading SM1-Threading SM2-Threading
Thickness
(Unmounted)
1.0 ± 0.25 mm  2.0 ± 0.10 mm
Clear Aperture 90% Outer Diameter
Surface Accuracy <2λ <5λ <2λc
Surface Quality 40-20 Scratch-Dig
Parallelism <3 arcmin <30 arcsec
Optical Density Tolerance ±5%
  • Click Link for Detailed Specifications on the Substrate
  • See the Threading Specs tab for dimensions and tolerances of these threads.
  • Over Ø25.0 mm Area within Clear Aperture
Mounted Item # Optical Density (@ 633 nm) Nominal Transmission
ND01A
ND501A
ND2R01A
0.1 79%
ND02A
ND502A
ND2R02A
0.2 63%
ND03A
ND503A
ND2R03A
0.3 50%
ND04A
ND504A
ND2R04A
0.4 40%
ND05A
ND505A
ND2R05A
0.5 32%
ND06A
ND506A
ND2R06A
0.6 25%
ND10A
ND510A
ND2R10A
1.0 10%
ND13A
ND513A
ND2R13A
1.3 5%
ND20A
ND520A
ND2R20A
2.0 1.0%
ND30A
ND530A
ND2R30A
3.0 0.10%
ND40A
ND540A
ND2R40A
4.0 0.01%
Optical Density Damage Thresholds
0.3 CWa 16 W/cm (532 nm, CW, Ø0.051 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.493 mm)
1.0 CWa 5 W/cm (532 nm, CW, Ø0.019 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.566 mm)
2.0 CWa 25 W/cm (532 nm, CW, Ø0.049 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.493 mm)
  • The power density of your beam should be calculated in terms of W/cm. For an explanation of why the linear power density provides the best metric for long pulse and CW sources, please see the Damage Thresholds tab.

Optical Density

Optical density (OD) indicates the attenuation factor provided by an optical filter, i.e. how much it reduces the optical power of an incident beam. OD is related to the transmission, T, by the equation
Optical Density Equation
where T is a value between 0 and 1. Choosing an ND filter with a higher optical density will translate to lower transmission and greater reflection of the incident light. For higher transmission and less reflection, a lower optical density would be appropriate. As an example, if a filter with an OD of 2 results in a transmission value of 0.01, this means the filter attenuates the beam to 1% of the incident power. Please note that the transmission data for our neutral density filters is provided in percent (%).

For Detailed Plot Information
 For More Info For individual transmission and optical density plots, as well as Excel files with raw data, click on this icon in the product tables below.
An Excel file with transmission and reflectance data for all N-BK7 Reflective ND filters is also available.
 Optical Density Transmission Reflectance
OD 0.1 - 0.6 Transmission OD 0.1 - 0.6
Click to Enlarge
Reflectivity OD 1.0 - 2.0
Click to Enlarge
OD 1.0 - 2.0 Transmission OD 0.1 - 0.6
Click to Enlarge
Visible transmission OD 1.0 - 2.0
Click to Enlarge
OD 3.0 - 4.0 Transmission OD 3.0 - 4.0
Click to Enlarge

Click for Transmission in the 400-700 nm Wavelength Range
Reflectivity OD 3.0 - 4.0
Click to Enlarge
Engraved Back of OAP
Click to Enlarge

Water Spectrum as Recorded Through a Standard and Wedged ND filter

Comparison of Standard and Wedged ND Filters
We present laboratory measurements on the difference in the etalon effect between our standard reflective neutral density (ND) filters and our wedged reflective ND filters. In many broadband scattering or absorption measurements, it is important to understand how intensity fluctuations through the utilized optics can impact the measurement. While it is known that parallel surfaces introduce significant wavelength-dependent intensity fluctuations, we find that utilizing a wedged geometry significantly reduces these etalon effects.

For our experiment we used the SLS202 Stabilized Light Source as the broadband, fiber-coupled light source. The F260FC-C Fiber Collimator, held in the KAD11F Kinematic Pitch/Yaw Adapter, collimates the light out of the fiber. The collimated light is incident upon the ND filter that is being investigated before entering the OSA203B Optical Spectrum Analyzer. The OSA has a spectral resolution of 7.5 GHz (0.25 cm-1) and the traces were averaged (>100 scans) in order to reduce noise and allow for more accurate analysis. The data focused on a wavelength range of 1820 - 1845 nm, which covers the NIR water spectrum. Since the absorption spectrum of water is well known, it is ideal to use as a comparison to evaluate the performance difference between these two styles of ND filter.

Lab Facts Complete Summary

The figure to the right summarizes the measured results for etalon effects through reflective neutral density filters. The etalon effects are quite stark, and we can see in the case of the standard ND filters that details of the water spectrum are lost to the intensity fluctuations of the background levels. By contrast, the wedged ND filters have a relatively clean signal with well-defined peaks. Data is presented for unmounted standard and wedged ND filters, though the results hold for mounted filters as well. Data is also compared to the HITRAN water spectrum standard. For details on the experimental setup employed and the results summarized here, please click here.

Damage Threshold Specifications
Optical Density Damage Thresholds
0.3 CWa 16 W/cm (532 nm, CW, Ø0.051 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.493 mm)
1.0 CWa 5 W/cm (532 nm, CW, Ø0.019 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.566 mm)
2.0 CWa 25 W/cm (532 nm, CW, Ø0.049 mm)
Pulsed 0.025 J/cm2 (532 nm, 10 ns, 10 Hz, Ø0.493 mm)
  • The power density of your beam should be calculated in terms of W/cm. For an explanation of why the linear power density provides the best metric for long pulse and CW sources, please see the "Continuous Wave and Long-Pulse Lasers" section below.

Damage Threshold Data for Thorlabs' Reflective ND Filters

The specifications to the right are measured data for Thorlabs' reflective neutral density filters. Damage threshold specifications are constant for a given optical density coating, regardless of the size of the filter.

 

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).

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.

Thorlabs' Threading Specifications

Thorlabs' lens tubes utilize a series of non-standard threadings. Threading specifications are given below for our SM threadings utilized in our lens tube and cage system components so that you can machine mating components to suit your application. We also offer products with C-Mount and RMS threadings, and the specifications for these threadings are also given below. Please note that other manufacturers may have different tolerances for these threads. For other thread specifications that are not listed here, please contact Tech Support.

SM05 Threading: Ø1/2" Lens Tubes, 16 mm Cage Systems
External Thread, 0.535"-40.0, UNS-2A Internal Thread, 0.535"-40.0, UNS-2B
Max Major Diameter 0.5340" Min Major Diameter 0.5350"
Min Major Diameter 0.5289" Min Pitch Diameter 0.5188"
Max Pitch Diameter 0.5178" Max Pitch Diameter 0.5230"
Min Pitch Diameter 0.5146" Min Minor Diameter (and 83.3% of thread) 0.508"
Max Minor Diameter 0.5069" Max Minor Diameter (and 64.9% of thread) 0.514"
RMS Threading: Objective, Scan, and Tube Lenses
External Thread, 0.800"-36.0, UNS-2A Internal Thread, 0.800"-36.0, UNS-2B
Max Major Diameter 0.7989" Min Major Diameter 0.8000"
Min Major Diameter 0.7934" Min Pitch Diameter 0.7820"
Max Pitch Diameter 0.7809" Max Pitch Diameter 0.7866"
Min Pitch Diameter 0.7774" Min Minor Diameter (and 83.3% of thread) 0.770"
Max Minor Diameter 0.7688" Max Minor Diameter (and 64.9% of thread) 0.777"
C-Mount Threading: Machine Vision LensesCCD/CMOS Cameras
External Thread, 1.000"-32.0, UN-2A Internal Thread, 1.000"-32.0, UN-2B
Max Major Diameter 0.9989" Min Major Diameter 1.0000"
Min Major Diameter 0.9929" Min Pitch Diameter 0.9797"
Max Pitch Diameter 0.9786" Max Pitch Diameter 0.9846"
Min Pitch Diameter 0.9748" Min Minor Diameter (and 83.3% of thread) 0.966"
Max Minor Diameter 0.9651" Max Minor Diameter (and 64.9% of thread) 0.974"
SM1 Threading: Ø1" Lens Tubes, 30 mm Cage Systems
External Thread, 1.035"-40.0, UNS-2A Internal Thread, 1.035"-40.0, UNS-2B
Max Major Diameter 1.0339" Min Major Diameter 1.0350"
Min Major Diameter 1.0288" Min Pitch Diameter 1.0188"
Max Pitch Diameter 1.0177" Max Pitch Diameter 1.0234"
Min Pitch Diameter 1.0142" Min Minor Diameter (and 83.3% of thread) 1.008"
Max Minor Diameter 1.0068" Max Minor Diameter (and 64.9% of thread) 1.014"
SM30 Threading: Ø30 mm Lens Tubes
External Thread, M30.5x0.5 Internal Thread, M30.5x0.5
Max Major Diameter 30.480 mm Min Major Diameter 30.500 mm
Min Major Diameter 30.371 mm Min Pitch Diameter 30.175 mm
Max Pitch Diameter 30.155 mm Max Pitch Diameter 30.302 mm
Min Pitch Diameter 30.059 mm Min Minor Diameter (and 83.3% of thread) 29.959 mm
Max Minor Diameter 29.938 mm Max Minor Diameter (and 64.9% of thread) 30.094 mm
SM1.5 Threading: Ø1.5" Lens Tubes
External Thread, 1.535"-40, UNS-2A Internal Thread, 1.535"-40, UNS-2B
Max Major Diameter 1.5339" Min Major Diameter 1.535"
Min Major Diameter 1.5288" Min Pitch Diameter 1.5188"
Max Pitch Diameter 1.5177" Max Pitch Diameter 1.5236"
Min Pitch Diameter 1.5140" Min Minor Diameter (and 83.3% of thread) 1.508"
Max Minor Diameter 1.5068" Max Minor Diameter (and 64.9% of thread) 1.514"
SM2 Threading: Ø2" Lens Tubes, 60 mm Cage Systems
External Thread, 2.035"-40.0, UNS-2A Internal Thread, 2.035"-40.0, UNS-2B
Max Major Diameter 2.0338" Min Major Diameter 2.0350"
Min Major Diameter 2.0287" Min Pitch Diameter 2.0188"
Max Pitch Diameter 2.0176" Max Pitch Diameter 2.0239"
Min Pitch Diameter 2.0137" Min Minor Diameter (and 83.3% of thread) 2.008"
Max Minor Diameter 2.0067" Max Minor Diameter (and 64.9% of thread) 2.014"
SM3 Threading: Ø3" Lens Tubes
External Thread, 3.035"-40.0, UNS-2A Internal Thread, 3.035"-40.0, UNS-2B
Max Major Diameter 3.0337" Min Major Diameter 3.0350"
Min Major Diameter 3.0286" Min Pitch Diameter 3.0188"
Max Pitch Diameter 3.0175" Max Pitch Diameter 3.0242"
Min Pitch Diameter 3.0133" Min Minor Diameter (and 83.3% of thread) 3.008"
Max Minor Diameter 3.0066" Max Minor Diameter (and 64.9% of thread) 3.014"

Posted Comments:
Qian Li  (posted 2019-07-05 09:18:43.26)
Hi Thorlabs! About these reflective neutral density filters, is the transmission is constant for different input power? Of course this is under the assumption that the input power is below the damage threshold. Thank you very much! Best, Qian Li
nbayconich  (posted 2019-07-08 10:42:29.0)
Thank you for contacting Thorlabs. The transmission percentage vs. input power will be constant for these filters. As you can see from our plots there will be some dependence on the wavelength.
linlinchiayu  (posted 2018-06-28 23:59:33.017)
Hello, I also want to know the Angle of incidence (AOI) limitations for these N-BK7 reflective ND filters. Can you share me the information of transmission and reflection data at different AOI's? Thank you.
YLohia  (posted 2018-07-03 10:25:26.0)
Hello, I have reached out to you directly with that data.
akhil.kanthamneni  (posted 2018-05-25 09:34:59.75)
Hello Thorlabs, Could you please let me know Angle of incidence (AOI) limitations for these N-BK7 reflective ND filters? I could not find any information on this in the product overvire page. Thank you Akhil
nbayconich  (posted 2018-05-25 05:08:49.0)
Thank you for contacting Thorlabs. These filters can be used a larger angles of incident but the amount of S & P transmission and reflection will change with increasing AOI. These reflective ND filters will not have a polarization dependence for transmission and reflectance if used at zero degrees AOI. I will reach out to you directly to share some transmission and reflection data at different AOI's.
jjurado  (posted 2011-08-18 09:22:00.0)
Response from Javier at Thorlabs to meier: We have tested the laser induced damage threshold (LIDT) of these reflective neutral density filters with a pulsed 532nm source, and arrived at a value of 0.025J/cm^2 (10 ns pulse width, 10 Hz rep. rate). However, the LIDT cannot reliably be scaled for a 1 s pulse using this value. In this case, a CW threshold is more appropriate. We specify a CW damage threshold of 0.75 W/cm^2 for these ND filters. With a 0.8W beam and 0.25mm^2 diameter, the resulting power density is 320W/cm^2, which greatly exceeds the CW spec. I will contact you directly for further support.
meier  (posted 2011-08-17 16:44:47.0)
Hi, question about the damage threshold: will the filter be damaged by a "short" laser pulse (532 nm) of about 1 second with a power of approx. 0.8W on an area of 0.25mm^2 ?
bdada  (posted 2011-07-21 10:32:00.0)
Response from Buki at Thorlabs: Please refer to the “Threading Specs” tab in the web page linked below to get the specifications for the SMx series Thorlabs threads. http://www.thorlabs.de/NewGroupPage9.cfm?ObjectGroup_ID=3307&pn=SM1L03#3388
jan.grawe  (posted 2011-07-21 10:20:47.0)
Hello, I need the full ppecs of the SM1 thread in order to design a mating part. Could you sent it to me? Best regards, Jan Grawé
jjurado  (posted 2011-05-10 09:54:00.0)
Response from Javier at Thorlabs to Felice: Thank you for contacting us. We would recommend using our reflective ND filters for use in the IR region. Even though their performance is most uniform in the 350-1100 nm range, they can still be used up to ~2 um. See Graphs tab above for reference. I will contact you directly with more information regarding the reflectance of these filters.
fg2251  (posted 2011-05-09 23:07:58.0)
Hi I need neutral density filter to attenuate fs pulse in IR 1.1-2 micron coming from an OPA (tens of microJ) Should I buy the ND series or the Absorbitive series NE? Also can you provide the transmittance in IR region? up to 2 micron? Thanks Felice
apalmentieri  (posted 2010-03-01 10:52:52.0)
A response from Adam at Thorlabs to lyu: We can make 1/2" diameter reflective filters for you. The price would be depended upon the quantity you are looking for as these would need a reflective inconel coating. I will email you directly to find out your quantity so we can get you an accurate price quote.
lyu  (posted 2010-03-01 09:46:48.0)
can you make diameter 1/2 inch reflective ND2 (BK7) filters for me? If can, how about the price? Thanks in advance. Yu
Tyler  (posted 2009-01-26 11:36:08.0)
A response from Tyler at Thorlabs to shshim: I hope that the custom spacers are working out. If we can help in any other way, please let us know.
shshim  (posted 2008-11-21 13:00:09.0)
Do you have any angled adapter to mount the reflective neutral density filters? Currently, I am using a cage filter wheel to hold 6 reflective ND filters. I fear that the reflected beam bounce back into the laser. The cage filter wheel doesnt allow to tilt the filters. I wish you have a simple angled ring that sits between the filter and the mount. I found your angled mount (SM1L03T), but this cannot be mounted to the filter wheel. I hope you have a good solution for this issue. Thanks!

Ø1/2" Mounted Reflective ND Filters

Item # Optical Densitya
(Transmission)
Transmission
Data
ND501A 0.1 (79%) info
ND502A 0.2 (63%) info
ND503A 0.3 (50%) info
ND504A 0.4 (40%) info
ND505A 0.5 (32%) info
ND506A 0.6 (25%) info
  • At 633 nm
Item # Optical Densitya
(Transmission)
Transmission
Data
ND510A 1.0 (10%) info
ND513A 1.3 (5%) info
ND520A 2.0 (1%) info
ND530A 3.0 (0.1%) info
ND540A 4.0 (0.01%) info

Click on More Info Icon for a plot and downloadable data. The black dashed line indicates the designated optical density.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ND501A Support Documentation
ND501AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.1
$43.56
Today
ND502A Support Documentation
ND502AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.2
$43.56
Today
ND503A Support Documentation
ND503AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.3
$43.56
Today
ND504A Support Documentation
ND504AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.4
$43.56
Today
ND505A Support Documentation
ND505AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.5
$43.56
Today
ND506A Support Documentation
ND506AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 0.6
$43.56
Today
ND510A Support Documentation
ND510AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 1.0
$43.56
Today
ND513A Support Documentation
ND513AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 1.3
$43.56
Today
ND520A Support Documentation
ND520AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 2.0
$49.23
Today
ND530A Support Documentation
ND530AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 3.0
$49.23
Today
ND540A Support Documentation
ND540AReflective Ø1/2" ND Filter, SM05-Threaded Mount, Optical Density: 4.0
$49.23
Today

Ø25 mm Mounted Reflective ND Filters

Item # Optical Densitya
(Transmission)
Transmission
Data
ND01A 0.1 (79%) info
ND02A 0.2 (63%) info
ND03A 0.3 (50%) info
ND04A 0.4 (40%) info
ND05A 0.5 (32%) info
ND06A 0.6 (25%) info
  • At 633 nm
Item # Optical Densitya
(Transmission)
Transmission
Data
ND10A 1.0 (10%) info
ND13A 1.3 (5%) info
ND20A 2.0 (1%) info
ND30A 3.0 (0.1%) info
ND40A 4.0 (0.01%) info

Click on More Info Icon for a plot and downloadable data. The black dashed line indicates the designated optical density.

Kit Item # Included Filters
NDK01 ND01A, ND02A, ND03A, ND04A, ND05A, ND06A, ND10A, ND20A, ND30A, ND40A
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ND01A Support Documentation
ND01AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.1
$63.30
Today
ND02A Support Documentation
ND02AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.2
$63.30
Today
ND03A Support Documentation
ND03AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.3
$63.30
Today
ND04A Support Documentation
ND04AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.4
$63.30
Today
ND05A Support Documentation
ND05AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.5
$63.30
Today
ND06A Support Documentation
ND06AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 0.6
$63.30
Today
ND10A Support Documentation
ND10AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 1.0
$63.30
5-8 Days
ND13A Support Documentation
ND13AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 1.3
$69.26
Today
ND20A Support Documentation
ND20AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 2.0
$75.48
5-8 Days
ND30A Support Documentation
ND30AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 3.0
$75.48
Today
ND40A Support Documentation
ND40AReflective Ø25 mm ND Filter, SM1-Threaded Mount, Optical Density: 4.0
$75.48
Lead Time
NDK01 Support Documentation
NDK01Box with 10 Reflective ND Filters, Ø25 mm, SM1 Mounted, 350 - 1100 nm
$675.24
5-8 Days

Ø50 mm Mounted Reflective ND Filters

Item # Optical Densitya
(Transmission)
Transmission
Data
ND2R01A 0.1 (79%) info
ND2R02A 0.2 (63%) info
ND2R03A 0.3 (50%) info
ND2R04A 0.4 (40%) info
ND2R05A 0.5 (32%) info
ND2R06A 0.6 (25%) info
  • At 633 nm
Item # Optical Densitya
(Transmission)
Transmission
Data
ND2R10A 1.0 (10%) info
ND2R13A 1.3 (5%) info
ND2R20A 2.0 (1%) info
ND2R30A 3.0 (0.1%) info
ND2R40A 4.0 (0.01%) info

Click on More Info Icon for a plot and downloadable data. The black dashed line indicates the designated optical density.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ND2R01A Support Documentation
ND2R01ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.1
$98.41
Today
ND2R02A Support Documentation
ND2R02ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.2
$98.41
Today
ND2R03A Support Documentation
ND2R03ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.3
$98.41
Today
ND2R04A Support Documentation
ND2R04ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.4
$98.41
Today
ND2R05A Support Documentation
ND2R05ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.5
$98.41
Today
ND2R06A Support Documentation
ND2R06ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 0.6
$98.41
Today
ND2R10A Support Documentation
ND2R10ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 1.0
$98.41
Today
ND2R13A Support Documentation
ND2R13ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 1.3
$98.57
Today
ND2R20A Support Documentation
ND2R20ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 2.0
$110.76
Today
ND2R30A Support Documentation
ND2R30ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 3.0
$110.76
Today
ND2R40A Support Documentation
ND2R40ACustomer Inspired! Reflective Ø50 mm ND Filter, SM2-Threaded Mount, Optical Density: 4.0
$110.76
Today

Storage Boxes for SM-Mounted Lenses and Filters

Product Image
(Click to Enlarge)
KT01KT04KT06
Item #KT01KT04KT06
Capacity1035a10
Quantity111
Optic SizeØ1"Ø1"Ø2" (Thickness = 1/2")
  • 26 Optics with Thickness = 0.45" (11.4 mm); 9 Optics with Thickness = 0.65" (16.5 mm)
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
KT01 Support Documentation
KT01Storage Box for Mounted Ø1" (25 mm) Round Optics (Max. Capacity: 10)
$95.77
Today
KT04 Support Documentation
KT04Storage Box for Mounted Ø1" Round Optics (26 Slots: 0.45" Thick; 9 Slots: 0.65" Thick)
$141.76
Today
KT06 Support Documentation
KT06Storage Box for Mounted Ø2" Round Optics (Max. Capacity: 10)
$95.77
Today
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