Brewster Windows

Uncoated UV Fused Silica Brewster Windows
Parallelism: ≤5 arcsec
Zero Reflection Loss for P-Polarized Light

BW0801

BW1602

BW0601

BW2502

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Overview
Graphs
Brewster Windows
Feedback
BS Selection Guide

Click to Enlarge
This graph shows the calculated reflectance of uncoated UV fused silica for polarized light at various angles of incidence. The reflectance for p-polarized light goes to zero at Brewster's angle.

Features

Ideal for Laser Cavities
UV Fused Silica Substrate
Available Minor Diameters: 6 mm, 8 mm, 13 mm, 16 mm, 20 mm, and 25 mm
P-Polarized Light is Transmitted without Reflection Losses
Brewster Window Mounts Available

Brewster Windows are uncoated substrates that can be used in series as polarizers, or to clean up a partially polarized beam. When positioned at Brewster's Angle, the p-polarized component of the light enters and exits the window without reflection losses, while the s-polarized component is partially reflected. The graph to the right shows reflectance for both s- and p-polarization through UV fused silica at 633 nm. The 20-10 scratch-dig surface quality and λ/10 transmitted wavefront error of our Brewster windows make them an ideal choice for laser cavities.

These Brewster windows are manufactured from UV fused silica, which exhibits virtually no laser-induced fluorescence (as measured at 193 nm), making it an ideal choice for applications from the UV to the near IR; please see the Graphs tab for a transmission plot of UV fused silica. Since the index of refraction of UV fused silica varies with wavelength, Brewster's angle is wavelength dependent; the Graphs tab also contains details on this dependence.

We offer mounting options for 8 mm, 13 mm, 16 mm, 20 mm, and 25 mm minor diameter Brewster windows. These mounts are engineered with a 55° 32’ mounting angle (Brewster’s Angle at 633 nm) with an exit port for the reflected S-polarized light so that the mount may be used in either direction.

We also offer a Brewster Window View Port for use in vacuum systems and Empty Glass Cells with Brewster Windows for spectroscopy applications. In addition to Brewster windows, Thorlabs also offers High Precision Windows, Narrowband Laser Windows, and a complete line of polarization optics.

UV Fused Silica Transmission, Index of Refraction, and Brewster's Angle

Click to Enlarge
This graph shows the calculated reflectance of uncoated UV fused silica for polarized light as a function of angle of incidence. The reflectance for p-polarized light goes to zero at Brewster's angle.

Click to Enlarge
This graph shows the transmission of a 1 mm thick UV fused silica sample, including surface reflections, with the incident light normal to the surface.

$UVFS Index of Refraction$
Click to Enlarge
This graph shows the calculated index of refraction of UV fused silica as a function of wavelength from 200 nm to 2.2 μm.

Click to Enlarge
This graph shows the calculated value of Brewster's angle as a function of wavelength when light is passing from air to UV fused silica.

The index of refraction for UV fused silica is wavelength dependent, as shown in the graph above, and expressed by the following formula:

$Index of Refraction for Fused Silica wavelength dependency$ .

Please note that that the wavelength needs to be in microns when using the formula above. Brewster's angle is given by

Brewster's Angle Equation .

Here, θ_B is Brewster's angle, n_i is the index of refraction of the incident medium (1.0003 for air), and n_t is the index of refraction of the transmitting medium (1.45701 for fused silica at 633 nm). Hence, Brewster's angle also displays a wavelength dependence, as shown in the plot above.

The image above shows the reflection of s-polarized light and transmission of p-polarized light through a Brewster window. Some s-polarized light will be transmitted through the window.

Brewster Windows

Brewster windows are typically used as polarizers within laser cavities. When positioned at Brewster's angle (55° 32' at 633 nm), the p-polarized portion of the light will pass through the window with no losses, while a fraction of the s-polarized portion will be reflected off the Brewster window. When used in a laser cavity, the Brewster window essentially acts as a polarizer.

Brewster's angle is given by

θ_B is Brewster's angle.
n_i is the index of refraction of the incident medium, which is 1.0003 for air.
n_t is the index of refraction of the transmitting medium, which is 1.45701 for fused silica at 633 nm

It should be noted that the index of refraction is wavelength dependent. For fused silica, the index of refraction can be expressed as

$Index of Refraction for Fused Silica wavelength dependency$ .

Please note that that the wavelength needs to be in microns when using the formula above.

Posted Comments:

m lieb (posted 2023-11-30 13:51:35.523)

Hi, am I assuming correctly that only one of the "edges" of the window has a bevel whereas the other one is "pointy"?. I would like to transmit as close as possible to the edge

cdolbashian (posted 2023-12-15 09:15:31.0)

Thank you for reaching out to us with this inquiry. The obtuse angles of this element have no bevel, while the acute angles have a small bevel. I have contacted you directly with a drawing which will, hopefully, be helpful for clarity.

prathmesh ghag (posted 2022-04-22 16:04:17.86)

For BW 2502 the transmission wavefront error is λ/10. Kindly let me know the transmission wavefront error specification offered for this product.

jdelia (posted 2022-05-16 04:08:47.0)

Thank you for contacting Thorlabs. Like you mentioned, we specify the transmitted wavefront error as <λ/10. I have contacted you directly to clarify your inquiry further

Ramon.alvarez (posted 2018-05-14 20:58:04.127)

What is the roughness of you elliptical Brewster windows?

YLohia (posted 2018-05-15 10:10:42.0)

Hello, thank you for contacting Thorlabs. While we do not have an official specification for the surface roughness for these units, it is typically on the order of < 5 Å.

dt_m0hammed_temimi (posted 2016-08-21 11:19:12.747)

please I need a brewster window with amount using with intracavity Nd:YAG laser

jlipa (posted 2013-10-25 14:36:32.427)

I need some Brewster windows like BW1602, but made from IR grade fused silica. Can you supply them?

tcohen (posted 2013-10-29 13:11:00.0)

Response from Tim at Thorlabs: Yes, we can quote this. We will contact you to discuss your requirements.

jack (posted 2009-05-26 15:21:13.0)

Response from Jack at Techsupport: If you look at the surface at 0 deg. then youll see a circular surface, at any other angle the surface will appear to be elliptical. The models are fine but the front view in drawing needs to be corrected. Optic department has been informed.

csandberg (posted 2009-05-26 05:24:03.0)

The solid model for these brewster windows seem to be wrong. The flat surfaces of the window should be elliptical when viewed perpendicular, and circular when viewed from the brewster angle. PS. Also see Lars Sandtroms comment on BW0601 earlier. It goes for all windows in this section.

lsandstrom (posted 2009-05-26 02:34:45.0)

BW0601 seems to be associated with the wrong SolidWorks model. The front surface of the model is circular in the Solid model while elliptical on the real device.

Laurie (posted 2009-05-01 13:36:20.0)

Response from Laurie at Thorlabs to egualda: Thank you for your interest in our Brewster Windows. At this time, we do not carry a standard mount for these optics. However, I have emailed a member of our mechanics unit to see if he has any ideas that we can share with you or any previous prototypes that may work.

egualda (posted 2009-04-30 11:16:20.0)

Do you have any spetial holder for the following item: BW0801 Brewster Window, 8mm diameter 1 mm thickness?

Beamsplitter Selection Guide

Thorlabs' portfolio contains many different kinds of beamsplitters, which can split beams by intensity or by polarization. We offer plate and cube beamsplitters, though other form factors exist, including pellicle and birefringent crystal. For an overview of the different types and a comparison of their features and applications, please see our overview. Many of our beamsplitters come in premounted or unmounted variants. Below is a complete listing of our beamsplitter offerings. To explore the available types, wavelength ranges, splitting/extinction ratios, transmission, and available sizes for each beamsplitter category, click More [+] in the appropriate row below.

Plate Beamsplitters

Non-Polarizing Plate Beamsplitters

Polarizing Plate Beamsplitters

45° AOI Unless Otherwise Noted
30 arcmin Wedge on Round Optics Only
Designed for use with P-polarized light.

Cube Beamsplitters

Non-Polarizing Cube Beamsplitters

Polarizing Cube and Polyhedron Beamsplitters

Pellicle Beamsplitters

Non-Polarizing Pellicle Beamsplitters

Crystal Beamsplitters

Polarizing Crystal Beamsplitters

Mounted in a protective box, unthreaded ring, or cylinder.
Available unmounted or mounted in a protective box or unthreaded cylinder.

Other

Other Beamsplitters

UV Fused Silica Brewster Windows, Uncoated

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Item #	BW0601	BW0801	BW0802	BW1302^a	BW1602	BW2002	BW2502
Minor Diameter	6.0 mm	8.0 mm	8.0 mm	13.0 mm	16.0 mm	20.0 mm	25.0 mm
Minor Diameter Tolerance	+0.00 / -0.10 mm
Thickness	1.0 mm		2.0 mm
Thickness Tolerance	±0.1 mm				±0.2 mm	±0.1 mm
Brewster Angle	55° 32' @ 633 nm
Clear Aperture	>90% of Minor Axis
Parallelism	≤5 arcsec
Transmitted Wavefront Error^b	<λ/10
Surface Quality	20-10 Scratch-Dig
Wavelength Range	185 nm - 2.1 μm (Uncoated)
Substrate	UV Fused Silica^c
Transmission Data

We also offer this window integrated into a viewport for use in vacuum systems (Item # GC05BP).
Measured at 633 nm.
Click link for detailed specifications on the substrate.

Brewster Window Mounts

Zoom

BW25M with SM1P1 Adapter mounted in a KS1RS

Click to Enlarge

View Imperial Product List

Item #	Qty	Description
BW2502	1	UVFS Brewster Window, 25.0 mm Minor Diameter, 2.0 mm Thick
BW25M	1	Brewster Window Mount, 25 mm Minor Axis Length, 2 mm Thick Optic
KS1RS	1	Kinematic Rotation Mount for Ø1" Optics
TR4	1	Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 4"

View Metric Product List

Item #	Qty	Description
BW2502	1	UVFS Brewster Window, 25.0 mm Minor Diameter, 2.0 mm Thick
BW25M	1	Brewster Window Mount, 25 mm Minor Axis Length, 2 mm Thick Optic
KS1RS	1	Kinematic Rotation Mount for Ø1" Optics
TR100/M	1	Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 100 mm

BW2502 Brewster Window in BW25M Mount with a KS1RS Kinematic Rotation Mount

These Brewster Window Optic Mounts are designed with steel flexure retention plates for holding the optics in place. The mounts feature a separate mounting surface for compatibility with Ø1/2" or Ø1" smooth bore mounts or internally SM1-threaded components. The exit port for the reflected S-polarized light allows the mount to be used in either direction. For more information, please see our full presentation here.

Brewster Window Mount Item #	Mounting Surface^a	Compatible Brewster Window
Brewster Window Mount Item #	Mounting Surface^a	Minor Diameter	Thickness	Brewster Window Item #
BW08M1	Ø1/2" Smooth Bore	8 mm	1 mm	BW0801
BW08M2	Ø1/2" Smooth Bore	8 mm	2 mm	BW0802
BW13M	Ø1" Smooth Bore	13 mm	2 mm	BW1302
BW16M		16 mm	2 mm	BW1602
BW20M		20 mm	2 mm	BW2002
BW25M	External SM1	25 mm	2 mm	BW2502

The mounting surface is the surface for attaching a Brewster window mount to a kinematic mount or other optomechanical device.

Type	Wavelength Range	Splitting Ratio (R:T)	Typical Reflectance^a (Click for Plot)	Typical Transmission^a (Click for Plot)	Backside AR Coating	Available Wedged	Available Sizes (Unmounted)
Economy	450 - 650 nm	30:70			No	No	Ø1" and Ø2"
Economy	450 - 650 nm	50:50			No	No	Ø1" and Ø2"
UV Fused Silica for UV	250 - 450 nm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
UV Fused Silica for UV to NIR	350 - 1100 nm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
UV Fused Silica for Visible	400 - 700 nm	10:90			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
		30:70
		50:50
		70:30
		90:10
UV Fused Silica for Visible to IR	600 - 1700 nm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
UV Fused Silica for NIR	700 - 1100 nm	10:90			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
		30:70
		50:50
		70:30
		90:10
UV Fused Silica for NIR	1.2 - 1.6 µm	10:90			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
		30:70
		50:50
		70:30
		90:10
IR Fused Silica for IR	0.9 - 2.6 µm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
CaF₂ for IR	1.0 - 6.0 µm	50:50			No	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
CaF₂ for IR	2.0 - 8.0 µm	50:50			No	Yes^b	Ø1/2", Ø1", and Ø2"
ZnSe for IR	1.0 - 12.0 µm	50:50			Yes	Yes^b	Ø1"
ZnSe for IR	7.0 - 14.0 µm	50:50			Yes	Yes^b	Ø1/2", Ø1", and Ø2"
Laser Line for Nd: YAG	532 nm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
Laser Line for Nd: YAG	1064 nm	50:50			Yes	Yes^b	Ø1/2", Ø1", 25 x 36 mm, and Ø2"
Polka Dot	250 nm - 2.0 µm	50:50	0° and 8° 45°		No	No	Ø1", 1" x 1", and Ø2"
	350 nm - 2.0 µm		0° and 8° 45°		No	No	Ø1", 1" x 1", and Ø2"
	180 nm - 8.0 µm		0° and 12° 45°		No	No	Ø1" and Ø2"
Ultrafast with Controlled GDD^c	600 - 1500 nm	20:80			Yes	No	Ø1"
		50:50
		80:20
		90:10
	1000 - 2000 nm	50:50

Type	Center Wavelength	Extinction Ratio (T_P:T_S)	Typical Transmission^a (Click for Plot)	Backside AR Coated	Available Wedged	Available Sizes (Unmounted)
Standard	405 nm	>10 000:1		No	Yes^b	Ø1" and 25 mm x 36 mm
	532 nm
	633 nm
	780 nm
	808 nm
	1030 nm
	1064 nm
	1310 nm
	1550 nm

Type	Wavelength Range	Splitting Ratio (R:T)	Typical Transmission (Click for Plot)	AR Coated Faces (Click for Plot)	Cemented	Available Cube Side Length
Visible: Unmounted 16 mm Cage Cube 30 mm Cage Cube	400 - 700 nm	10:90			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		30:70			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		50:50			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1", and 2" Mounted: 20 mm in a 16 mm Cage Cube, 1" in a 30 mm Cage Cube
		70:30			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		90:10			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
NIR: Unmounted 16 mm Cage Cube 30 mm Cage Cube	700 - 1100 nm	10:90			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		30:70			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		50:50			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1", and 2" Mounted: 20 mm in a 16 mm Cage Cube, 1" in a 30 mm Cage Cube
		70:30			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		90:10			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
IR: Unmounted 16 mm Cage Cube 30 mm Cage Cube	1100 - 1600 nm	10:90			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		30:70			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		50:50			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1", and 2" Mounted: 20 mm in a 16 mm Cage Cube, 1" in a 30 mm Cage Cube
		70:30			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1"
		90:10			Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm,1"

Type	Wavelength Range	Extinction Ratio (T_P:T_S)	Typical Transmission	AR Coated Faces	Cemented	Available Cube/ Polyhedron Side Length
Standard: Unmounted 16 mm Cage Cube 30 mm Cage Cube	420 - 680 nm	>1000:1		Yes	Yes	Unmounted: 5 mm, 10 mm, 1/2", 20 mm, 1", and 2" Mounted: 20 mm in a 16 mm Cage Cube, 1" in a 30 mm Cage Cube
	620 - 1000 nm
	700 - 1300 nm
	900 - 1300 nm
	1200 - 1600 nm
Wire Grid: Unmounted 30 mm Cage Cube	400 - 700 nm	>1000:1 (AOI: 0° - 5°) >100:1 (AOI: 0° - 25°)	P-Pol. S-Pol.	Yes	Yes	Unmounted: 1" Mounted: 20 mm in a 16 mm Cage Cube, 1" in a 30 mm Cage Cube
High-Power Laser Line: Unmounted 30 mm Cage Cube	355 nm	>2000:1			No	Unmounted: 1/2" and 1" Mounted: 1" in a 30 mm Cage Cube
	405 nm
	532 nm
	633 nm
	780 - 808 nm
	1064 nm
Laser Line: Unmounted 30 mm Cage Cube	532 nm	>3000:1		Yes	Yes	Unmounted: 10 mm, 1/2", and 1" Mounted: 1" in a 30 mm Cage Cube
	633 nm
	780 nm
	980 nm
	1064 nm
	1550 nm
High-Power, Broadband, High Extinction Ratio Polarizers	700 - 1100 nm	>1000:1 (700 - 1100 nm) >5000:1 (750 - 1000 nm) >10 000:1 (800 - 900 nm)		Yes	No	12.7 mm (Input/Output Face, Square)
	900 - 1300 nm	>1000:1 (900 - 1300 nm) >10 000:1 (900 - 1250 nm) >100 000:1 (980 - 1080 nm)				10.0 mm and 5.0 mm (Input/Output Face, Square)
Laser-Line Variable	532 nm	Not Specified	No Graph Available	Yes	Yes	Assembly Mounted in a 30 mm Cage Cube
	633 nm
	780 nm
	1064 nm
	1550 nm
Broadband Variable	420 - 680 nm	Not Specified	No Graph Available	Yes	Yes	Assembly Mounted in a 30 mm Cage Cube
	690 - 1000 nm
	900 - 1200 nm
	1200 - 1600 nm
Circular Polarizer/Beamsplitter	532 nm	Not Specified	No Graph Available	Yes	Yes	Assembly Mounted in a 30 mm Cage Cube
	633 nm
	780 nm
	1064 nm
	1550 nm

Type	Wavelength Range	Splitting Ratio (R:T)	Typical Reflectance^a (Click for Plot)	Typical Transmission^a (Click for Plot)	Available Sizes
Pellicle: Unmounted 30 mm Cage Cube	400 - 2400 nm	8:92			Unmounted: Ø1/2", Ø1", and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	300 - 400 nm	45:55			Unmounted: Ø1" and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	400 - 700 nm	45:55			Unmounted: Ø1/2", Ø1", and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	635 nm	33:67			Unmounted: Ø1/2", Ø1", Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	635 nm	50:50			Unmounted: Ø1/2", Ø1", and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	700 - 900 nm	45:55			Unmounted: Ø1/2", Ø1", and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	1.0 - 2.0 µm	45:55			Unmounted: Ø1/2", Ø1", and Ø2" Mounted: Ø1" in a 30 mm Cage Cube
	3.0 - 5.0 µm	45:55			Unmounted: Ø1/2" and Ø1" Mounted: Ø1" in a 30 mm Cage Cube

Type	Wavelength Range	Splitting Ratio	Substrate Transmission	Typical Reflectance	Available Sizes (Unmounted)
Wedged Plate Beamsplitter	185 nm - 2.1 µm	-		-	2" x 1" (L x H) 8.0 mm (Middle Thickness) Wedge Angle: 5°
Brewster Windows	185 nm - 2.1 µm	-			6.0 mm, 8.0 mm, 13.0 mm, 16.0 mm, 20.0 mm, and 25.0 mm (Minor Diameters)

Type	Wavelength Range	Extinction Ratio (T_P:T_S)	Typical Beam Separation Angle (Click for Representative Diagram)	Typcial Substrate Transmission (Click for Plot)	Typical Coating Reflectance (Click for Plot)	Cemented	Available Sizes
Calcite Beam Displacers	350 nm - 2.3 µm	Not Specified	Parallel with 2.7 mm Spacing at 1500 nm		Uncoated	No	10 mm^a (Clear Aperture, Square)
			Parallel with 4.0 mm Spacing at 1500 nm				10 mm^a (Clear Aperture, Square)
Yttrium Orthovanadate Beam Displacer	488 nm - 3.4 µm	Not Specified	Parallel with 1.2 mm Spacing at 2000 nm		Uncoated	No	>3 mm x 5 mm^b (Clear Aperture, Ellipse)
	2.0 µm
Wollaston Prisms	400 nm - 2.0 µm	>10 000:1	1° at 633 nm		Uncoated	Yes	Ø10 mm^a (Clear Aperture)
	200 nm - 6.0 µm	>10 000:1	1° 20' at 633 nm		Uncoated		Ø10 mm^a (Clear Aperture)
	190 nm - 3.5 µm	>100 000:1	20° at 250 nm		Protective MgF₂ (No Data)		Ø10 mm^a (Clear Aperture)
	350 nm - 2.3 µm	>100 000:1	20° at 633 nm		Uncoated		Ø10 mm^b (Clear Aperture)
							Ø10 mm^a (Clear Aperture)
							Ø10 mm^a (Clear Aperture)
	900 nm - 3.4 µm	>100 000:1	20° at 633 nm		Uncoated		Ø10 mm^a (Clear Aperture)
Rochon Prisms	200 nm - 6.0 µm	>10 000:1	1.5° at 4 µm		Uncoated	Yes	10 mm x 10 mm^a (Min Clear Aperture)
	488 nm - 3.4 µm	>100 000:1	10.6° at 2 µm