The high-performance, multilayer broadband A coating deposited on each filter is designed to minimize surface reflections within the 350 - 700 nm range, thereby reducing the amount of stray light present. These coatings provide an average reflectance that is less than 0.5% per surface over the specified wavelength range when light is normally incident on the filter surface. Typical transmission data is shown by clicking on the blue info icons () in the tables below.
Unlike metallic neutral density filters, each absorptive ND filter is fabricated from one member of a family of Schott glasses (see the Specs tab for more information). Each Schott glass has a spectrally flat absorption coefficient. By varying the type of glass used and the thickness of that glass, we are able to produce our entire line of absorptive ND filters from just four types of Schott glass. See below for detailed information about the average transmission obtained with each of our AR-coated absorptive neutral density filters.
Optical Density and Transmission 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
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 absorption of the incident light. For higher transmission and less absorption, 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 (%).
Please note that these products are not designed for use 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 stray light.
Transmission and Optical Density of -A Coated ND Filters. The values in the legend are the typical optical densities at 633 nm for each optic prior to coating. The blue shaded region indicates the wavelength range for which the AR coating performance is specified.
Optical Density (OD)a
OD Tolerancea
Substrate
Substrate Thicknessb
Ø1/2" Item #
Ø25 mm Item #
0.1
±0.005
NG11
0.6 mm
NE501B-A
NE01B-B
0.2
±0.01
NG11
1.4 mm
NE502B-A
NE02B-B
0.3
±0.015
NG11
2.3 mm
NE503B-A
NE03B-B
0.4
±0.02
NG4
0.7 mm
NE504B-A
NE04B-B
0.5
±0.025
NG4
0.9 mm
NE505B-A
NE05B-B
0.6
±0.03
NG4
1.1 mm
NE506B-A
NE06B-B
0.7
±0.04
NG4
1.3 mm
NE507B-A
NE07B-B
0.8
±0.05
NG4
1.5 mm
NE508B-A
NE08B-B
0.9
±0.05
NG4
1.7 mm
NE509B-A
NE09B-B
1.0
±0.05
NG4
1.9 mm
NE510B-A
NE10B-B
1.3
±0.065
NG4
2.5 mm
NE513B-A
NE13B-B
1.5
±0.08
NG4
2.9 mm
NE515B-A
NE15B-B
2.0
±0.1
NG9
1.4 mm
NE520B-A
NE20B-B
3.0
±0.15
NG9
2.1 mm
NE530B-A
NE30B-B
4.0
±0.2
NG9
2.8 mm
NE540B-A
NE40B-B
5.0
±0.25
NG9
3.6 mm
NE550B-A
NE50B-B
6.0
±0.3
NG1
1.5 mm
NE560B-A
NE60B-B
Measured at 633 nm before the AR coating is applied. See the tables below for a plot of typical transmission for each filter.
Values given are typical. The actual thickness of each ND filter is dependent on the optical density of the lot of glass used to manufacture each lot of ND filters.
General Specifications
Diameter
12.7 mm
25.0 mm
Diameter Tolerance
+0.00 / -0.25 mm
Clear Aperture
>90% Outer Diameter
AR Coating Range
350 - 700 nm
Reflectance (Average)
<0.5% per Surfacea
Surface Flatnessb
<λ/4 (OD = 0.7, 0.8, 0.9, or 1.5) λ/4 (All Other ODs)
Surface Quality
40-20 Scratch-Dig
Parallelism
<3 arcmin (OD = 0.7, 0.8, 0.9, or 1.5); 3 arcmin (All Other ODs)
<10 arcsec (OD = 0.7, 0.8, 0.9, or 1.5) 10 arcsec (All Other ODs)
At 0° AOI
At 633 nm
The shaded regions in the graphs below denote the wavelength range for which the AR coating performance is specified. Click here to download optical density and transmission data. For the transmission and optical density of a particular filter, please click in the row corresponding to the filter in the tables below.
Click to Enlarge Click Here for Raw Data The blue shaded region indicates the specified 350 - 700 nm wavelength range for optimum performance.
Posted Comments:
n house
 (posted 2019-04-16 18:55:24.933)
I recently purchased these unmounted AR-coated ND filters. Are the OD plots you show on your website the plots I should expect, or can the intensity of transmission change slightly from batch-to-batch?
YLohia
 (posted 2019-04-17 09:08:16.0)
Hello, thank you for contacting Thorlabs. The plots shown on the website are typical, so there would be a slight batch-to-batch variation over the specified operating range. Since these are AR-coated, there may be more significant variations in the out-of-band regions between different batches.
gilliss
 (posted 2017-02-22 12:26:04.373)
Looking at plots such as
https://www.thorlabs.com/images/TabImages/ND_Filters_A-Coated_Optical_Density_All_780.gif
and then
https://www.thorlabs.com/images/TabImages/ND_Filters_A-Coated_Optical_Density_Rest_780.gif
I'm confused as to why all of the features in ND2.0 filters and up seem to shift over by 50nm. Could this be a measurement error? By these plots, all filters below OD2.0 seem appropriate for the stated wavelength range of 350 to 700, but the higher ones seem to only be useful above 400 nm.
jlow
 (posted 2017-03-01 04:46:47.0)
Response from Jeremy at Thorlabs: The reason there's a shift is because of the material used. The ND filters with OD2, 3, 4, and 5, are made from NG9 glass whereas the lower OD filters were made with NG4 or NG11 glass. You can see the type of glass used under the Specs tab.
Dear Sirs,
I would like to buy about 30 unmounted and AR-coated absorptive ND filters for both visible and NIR light at different OD, but I need bigger sizes, i.e. 37.0 +0.0/-0.2 mm: could it be possible to make such an order?
Thank you for your attention.
Best regards,
Michele Maiorano
besembeson
 (posted 2015-01-13 06:36:05.0)
Response from Bweh at Thorlabs: Yes we do provide custom sizes for these ND filters. I will followup with you by email for your OD, AR coating specifications and quotation.
Click the icon to view a plot of the typical filter transmission.
Measured before the AR coating is applied. See Transmission Data graphs for typical performance.
Values given are typical. The actual thickness of each ND filter is dependent on the optical density of the lot of glass used to manufacture each lot of ND filters.
Click the icon to view a plot of the typical filter transmission.
Measured before the AR coating is applied. See Transmission Data graphs for typical performance.
Values given are typical. The actual thickness of each ND filter is dependent on the optical density of the lot of glass used to manufacture each lot of ND filters.
Additional Neutral Density Filters: Absorptive/Reflective