Knife-Edge Right-Angle Prism Mirrors

Overview
Specs
Graphs
Feedback

Right Angle Prism Mirror Selection Guide
Metallic Coatings (250 nm - 20 µm)
Dielectric Coatings (400 nm - 1100 nm)
Laser Line (532 and 1064 nm)
Knife Edge (250 nm - 20 µm)

Features

Right-Angle Prism with Mirror-Coated Legs
"Knife Edge" Between the Two Coated Surfaces for Combining or Separating Beams
25 mm x 25 mm Reflective Surfaces

Thorlabs' Knife-Edge Right-Angle Prism Mirrors feature reflective coatings on the two legs and offer a clear aperture extending across the 90° angle between the coated surfaces. They are manufactured from N-BK7 and have 25 mm x 25 mm reflective legs. These prism mirrors are offered with one of the following reflective coatings: UV enhanced aluminum, protected aluminum, protected gold, or protected silver. Please see the Specs and Graphs tabs above for details on the reflectivity of the various coatings.

Click to Enlarge

The precision corner between the two coated surfaces allows two counterpropagating beams to be made collinear with the output orthogonal to the input, as shown in the figure to the left. They can also be used to split a single input beam aimed directly at the knife edge. The prisms are ideal for situations where it is undesirable to use a beamsplitting cube, such as due to the geometry of the setup. Some diffraction and scatter will occur whenever a beam is split using these prisms.

These prisms feature a coating that extends to the edge of the optic. Care should be used when handling the prisms, as the coated edge is very delicate and can be chipped easily.

While the hypotenuse is polished, these mirrors are not intended for use as retroreflectors due to the adhesion layers used in the coating process. As a result, no specifications are given for the polished hypotenuse of the prism. For retroreflection applications we suggest the PS911K, an uncoated version of our knife edge prism, or our selection of mounted and unmounted retroreflectors. Thorlabs also offers a selection of hypotenuse-coated right-angle prism mirrors.

Care and Handling
Silver coated mirrors require additional care due to their susceptibility to damage from environmental conditions and improper handling. Fingerprints, contact with abrasive surfaces, and environments with high humidity or temperature will diminish the effectiveness of the protective overcoat leaving the silver coating susceptible to oxidation and degradation. When working with silver mirrors, follow standard practices for handling optics. Latex gloves or similar protective coverings are recommended to prevent oil and other residues on the user’s fingers from reaching the optical surface. Even with such precautions, care should be taken not to touch the mirrored face or edges. Silver mirrors should be used and stored in areas at room temperature with minimal humidity. For information on how to clean mirrors and other optics, visit our Optic Cleaning Tutorial.

Item #	MRAK25-F01	MRAK25-G01	MRAK25-P01	MRAK25-M01
Coating (On Legs)	UV Enhanced Aluminum	Protected Aluminum	Protected Silver	Protected Gold
Reflectance^a	R_avg > 90% (250 -450 nm)	R_avg > 90% (450 - 2000 nm) R_avg > 95% (2 - 20 µm)	R_avg > 97% (450 - 2000 nm) R_avg > 96% (2 - 20 µm)	R_avg > 96% (800 nm - 20 µm)
Substrate Material	N-BK7
L^b	25.0 mm
X^b	35.4 mm
Clear Aperture (Coated Surfaces)	Entire Face Length and Width, Excluding a 1.25 mm Border Along All Beveled Edges
Clear Aperture (Hypotenuse)	90% of Face Length and Width
Surface Flatness (All Surfaces)	λ/8 @ 632.8 nm Over the Clear Aperture (Peak to Valley)
Surface Quality	20-10 Scratch-Dig

For an angle of incidence from 0° to 45°.
Defined in the diagram below.

All data shown below is for unpolarized light, unless otherwise stated. The shaded regions in the graphs denote the ranges over which we guarantee the specified reflectance. Please note that the reflectance outside of these bands is typical and can vary from lot to lot, especially in out-of-band regions where the reflectance is fluctuating or sloped.

UV-Enhanced Aluminum Coating (250 - 450 nm)

UV-Enhanced Aluminum at Near-Normal Incident Angle

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Excel Spreadsheet with Raw Data for UV-Enhanced Aluminum

UV-Enhanced Aluminum at 45 Degree Incident Angle

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Excel Spreadsheet with Raw Data for UV-Enhanced Aluminum

Protected Aluminum Coating (450 nm - 20 µm)

Protected Aluminum at Near-Normal Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Aluminum

Protected Aluminum at 45 Degree Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Aluminum

Protected Silver Coating (450 nm - 20 µm)

Protected Silver at Near-Normal Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Silver

Protected Silver at 45 Degree Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Silver

Protected Gold Coating (800 nm - 20 µm)

Protected Gold at Near-Normal Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Gold

Protected Gold at 45 Degree Incident Angle

Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Gold

Posted Comments:

Marshall Scott (posted 2019-10-21 14:37:34.193)

rstahl (posted 2018-05-01 14:47:00.51) How sharp is the knife edge? How small a beam diameter could I split with this part? YLohia (posted 2018-05-02 10:31:35.0) Hello, unfortunately, we do not specify an exact thickness of the knife edge on these prisms; we design the thickness of the edge as thin as our manufacturing abilities allow and is suited for general beamsplitting and beam combining applications. :(

YLohia (posted 2019-11-05 03:15:05.0)

We specify no chamfer on this surface to ensure working distance is available as close to the edge as possible. We are currently working on defining a specification as to how sharp that edge actually is. I will reach out to you via e-mail to discuss this further.

lebouquj (posted 2018-06-07 16:32:10.937)

Hello, Could you offer MRAK20-M01, that is with 20mm legs instead of 25mm ? Thanks, Jean-Baptiste

nbayconich (posted 2018-06-12 10:15:57.0)

Thank you for contacting Thorlabs. We can look into providing this custom for you. I will reach out to you directly with more information. For any custom requests please contact techsupport@thorlabs.com directly.

simon.neves (posted 2018-05-03 17:13:22.78)

Dear Sir/Madam, Do you provide a knife edge with dielectric coatic for 1550 nm wavelength ? Thank you for your help Simon Neves

YLohia (posted 2018-05-04 10:02:31.0)

Dear Simon, thank you for contacting Thorlabs. We do have the ability to provide these knife-edge right-angle prisms with our selection of dielectric coatings as specials. We will contact you directly for more details.

rstahl (posted 2018-05-01 14:47:00.51)

How sharp is the knife edge? How small a beam diameter could I split with this part?

YLohia (posted 2018-05-02 10:31:35.0)

Hello, unfortunately, we do not specify an exact thickness of the knife edge on these prisms; we design the thickness of the edge as thin as our manufacturing abilities allow and is suited for general beamsplitting and beam combining applications.

pierrick.cheiney (posted 2018-04-17 15:59:01.933)

Dear Sir/Madam, Could you provide knife-edge prism mirror in smaller size such as 5 or 10 mm width? Best regards, Pierrick Cheiney

YLohia (posted 2018-04-17 11:17:46.0)

Hello Pierrick, thank you for contacting Thorlabs. We will reach out to you directly to discuss the possibility of offering this.

yitzhak.malka (posted 2018-01-31 08:59:18.217)

Can you please indicate the 90degree angle accuracy?

nbayconich (posted 2018-02-07 04:19:12.0)

Thank you for contacting Thorlabs. The tolerance to the 90 degree angle is ±3 arcminutes.

cmullark (posted 2018-01-18 05:27:01.987)

I have a question: What is the thickness of the knife-edge? If I place the prism in the focal plane of a beam to split it than as I focus tighter and tighter there will be more scattering/loss determined primarily by the knife edge thickness. Would it be different between the dielectric coating and the protected silver? Thanks for any help you can provide in this matter.

nbayconich (posted 2018-03-30 04:25:50.0)

Thank you for contacting Thorlabs. We do not specify an exact thickness for either coating type of these knife edge prisms, we design the thickness of the edge as thin as our manufacturing abilities allow.

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