Selection Guide for Neutral Density Filters
Selection Guide for Neutral Density Filters		Absorptive
Uncoated (400 - 650 nm)	Mounted
Uncoated (400 - 650 nm)	Unmounted
Uncoated (800 - 2600 nm)	Mounted
Uncoated (800 - 2600 nm)	Unmounted
AR-Coated (350 - 700 nm)	Mounted
AR-Coated (350 - 700 nm)	Unmounted
AR-Coated (650 - 1050 nm)	Mounted
AR-Coated (650 - 1050 nm)	Unmounted
AR-Coated (1050 - 1650 nm)	Mounted
AR-Coated (1050 - 1650 nm)	Unmounted
Reflective
N-BK7 (350 - 1100 nm)	Mounted
N-BK7 (350 - 1100 nm)	Unmounted
UV Fused Silica (200 - 1200 nm)	Mounted
UV Fused Silica (200 - 1200 nm)	Unmounted
ZnSe (2 - 12 µm)	Mounted
ZnSe (2 - 12 µm)	Unmounted
Variable Reflective
Neutral Density Filter Kits

Features

Available with 25 mm or 1/2" Diameter
N-BK7 Substrate Attenuates Over the 350 to 1100 nm Wavelength Range
Optical Densities Ranging from 0.1 to 4.0

Thorlabs' Reflective (or Metallic) Neutral Density (ND) Filters provide uniform attenuation over the broad spectral range from 350-1200 nm. Our reflective ND 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.

These filters consist of a N-BK7 glass substrate with a metal (Inconel) coating. Inconel is a very hard metallic alloy that ensures flat spectral response from the UV to the mid IR and 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^oC.

Our N-BK7 reflective ND filters are also avaliable mounted in SM1-threaded (Ø25 mm) or SM05-threaded (Ø1/2") lens tubes. Thorlabs also offers UV fused silica and variable reflective ND filters, as well as a complete line of absorptive ND filters in several sizes; the table above 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, such as beam blocks, that significantly reduce exposure to the stray or reflected light.

General Specifications
Filter	NDxxB	ND5xxB
Substrate	N-BK7 Glass
Diameter	25.0 +0.0 / -0.5 mm	12.7 +0.0/-0.25mm
Thickness	1.0 ± 0.25 mm
Clear Aperture	90% Outer Diameter
Surface Accuracy	<5λ	<2λ
Surface Quality	40-20 Scratch-Dig
Parallelism	<3 arcmin

Item #	Optical Density (@ 633 nm)	Nominal Transmission
ND01B ND501B	0.1	79%
ND02B ND502B	0.2	63%
ND03B ND503B	0.3	50%
ND04B ND504B	0.4	40%
ND05B ND505B	0.5	32%
ND06B ND506B	0.6	25%
ND10B ND510B	1.0	10%
ND13B ND513B	1.3	5%
ND20B ND520B	2.0	1.0%
ND30B ND530B	3.0	0.10%
ND40B ND540B	4.0	0.01%

Item #	Damage Thresholds
ND503B ND03B	1000 W/cm² (532 nm, CW, Ø0.051 mm)
ND503B ND03B	0.025 J/cm² (532 nm, 10 ns, 10 Hz, Ø0.493 mm)
ND510B ND10B	1000 W/cm² (532 nm, CW, Ø0.019 mm)
ND510B ND10B	0.025 J/cm² (532 nm, 10 ns, 10 Hz, Ø0.566 mm)
ND520B ND20B	1000 W/cm² (532 nm, CW, Ø0.049 mm)
ND520B ND20B	0.025 J/cm² (532 nm, 10 ns, 10 Hz, Ø0.493 mm)

Optical Density

The optical density, OD, is defined in terms of transmission T by the following equation:
Optical Density Equation
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.

For Detailed Plot Information
	For plots for each item in terms of % transmission and derived optical density, as well as Excel files with plot data, click on this icon in the product tables.
An Excel file with transmission and reflection data for all BK7 Reflective ND filters is also available.

	Transmission	Reflectivity
OD 0.1-0.6	Click to Enlarge	Click to Enlarge
OD 1.0-2.0	Click to Enlarge	Click to Enlarge
OD 3.0-4.0	Click to Enlarge Click for Transmission in the 400-700 nm Wavelength Range	Click to Enlarge

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Posted Comments:

Poster: tcohen

Posted Date: 2013-02-21 14:55:00.0

Response from Tim at Thorlabs to Ryan: Thank you for contacting us. We have reflectivity data past 1100nm on the “Graphs” tab and I will contact you directly to provide typical plots on %T extended past 1100nm.

Poster: tcohen

Posted Date: 2012-05-22 11:55:00.0

Response from Tim at Thorlabs: Thank you for your interest in our Reflective ND Filters. We are able to quote many custom optics and I will contact you directly to get more information so that we may provide pricing and lead time.

Poster: yu.zhang

Posted Date: 2012-05-21 02:34:51.0

N-BK7 Reflective Neutral Density Filters We are interested in this product. But we need the size to be 180 mm x 180 mm. Can thorlab customize for us? What will be the piece price (10 pieces for example)? Thanks!

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Unmounted N-BK7 Reflective Neutral Density Filters

Features

Optical Density