Converging or Diverging
Converging Light

Collimated
Collimated Light

Features

Qualitative Beam Collimation Test for Beams with Diameters from 1 to 50 mm
Magnetically Coupled Kinematic Design Allows Shear Plates to be Interchanged Quickly
Imperial and Metric Threaded Mounting Holes

The SI Series of shearing interferometers can be used to determine if a coherent beam of light is collimated. The design consists of a wedged optical flat mounted at 45° and a diffuser plate with a ruled reference line down the middle. This interferometer is designed to provide qualitative analysis of a beam's collimation.

The diffuser plate is used to view the interference fringes created by Fresnel reflections from the front and back surfaces of the optical flat. If the beam is collimated, the resulting fringe pattern will be parallel to the ruled reference line. In addition to the degree of collimation, the fringes will also be sensitive to spherical aberration, coma, and astigmatism.

The wedged optical flat is made of uncoated UV fused silica. The wedge angle for each plate size is optimized for the range of the acceptable beam sizes; see the Specs tab for details. Since the light is incident on the plate at a 45° angle, the intensity of the fringe pattern is dependent on the polarization of the light. Maximum intensity will occur when the polarization is perpendicular to the plane of incidence.

In order to observe interference fringes, the coherence length of the incident light must be longer than the change in optical path length caused by the shear plate. See the table footnote on the Specs tab for more information.

Construction
The shearing interferometers come in an aluminum case as a set of three pieces: a base, a plate with the wedged optical flat, and a plate with the diffuser viewing screen. To set up the interferometer, attach the viewing screen plate to the base using the included 4-40 screws and hex key. The shear plate is held in place magnetically, allowing it to be easily swapped out for a plate with a different wedged optical flat.

The base is constructed from anodized aluminum and features tapped holes for mounting to Ø1/2" posts. Behind the wedged optical flat, a hole is bored through the base to allow the transmitted beam to pass through the optical flat unimpeded. For all models except the SI500, this hole is SM1-threaded (1.035"-40). The cross-sectional view to the right illustrates how the shearing interferometer is constructed as well as the laser beam's propagation path.

Accessories
For small beam diameters, the corresponding fringe pattern will also be small, which can make it difficult to see. For these situations, the SIVS Magnified Viewing Screen accessory can be purchased to replace the standard diffuser plate viewing screen, thereby increasing the size of the fringes on the diffuser plate. The SIVS consists of a mounted diverging lens and diffuser plate and can be used for beam diameters ranging from 1 mm to 10 mm. The plates containing the wedged optical flats are also available individually so that various beam sizes can be tested using a single base unit.

Item #	Wedge Angle	Diameter +0/-0.25 mm	Thickness ±0.25 mm	Approximate ΔOPL*	Dimensions (L x W x H) (mm)
SI035	117 arcsec	5.28 mm	0.75 mm	1.91 mm	50.8 x 48.3 x 55.9
SI050	83 arcsec	7.94 mm	1.30 mm	3.31 mm	50.8 x 48.3 x 55.9
SI100	40 arcsec	15.60 mm	2.60 mm	6.62 mm	50.8 x 48.3 x 55.9
SI254	18 arcsec	38.00 mm	6.35 mm	16.18 mm	50.8 x 48.3 x 55.9
SI500	10 arcsec	78.00 mm	13.00 mm	33.12 mm	116.8 x 133.4 x 134.6

*In order to ensure interference takes place, check to see that the effective coherence length of your source is longer than the approximate change in optical path length (ΔOPL). As the coherence length of your source approaches a few multiples of ΔOPL, the contrast of the interference fringes will decrease. Once the coherence length reaches the ΔOPL, you are effectively imaging incoherent light. This ΔOPL was calculated for UVFS (n=1.457 @ 632.8 nm) with the assumption of parallel reflective surfaces seperated by the thickness listed above.

Item #	Included Plate^a	Beam Diameter for Included Plate^b	Compatible Plates	Compatible Accessories	Threaded Mounting Holes
SI035	SI035P	1 - 3 mm	SI035P, SI050P, SI100P, and SI254P	SIVS, SITST^c	8-32 and M4
SI050	SI050P	2.5 - 5 mm	SI035P, SI050P, SI100P, and SI254P		8-32 and M4
SI100	SI100P	5 - 10 mm	SI035P, SI050P, SI100P, and SI254P		8-32 and M4
SI254	SI254P	10 - 25.4 mm	SI035P, SI050P, SI100P, and SI254P	SIVS^d	8-32 and M4
SI500	SI500P	25.4 - 50 mm	SI500P		1/4"-20 and M6

^a The wedged plates are made from UVFS
^b Different plates with differing wedge angles are offered for different sized beams. This is to optimize the separation between the plates for particular beam diameters, and thus produce an interference pattern.
^c Mechanical Dimensions: Ø30.5 mm x 50.0 mm
^d The SIVS is designed for viewing the small fringes created by small-diameter beams. It is compatible with the SI254, but is not intended or necessary for viewing the fringes of the larger diameter beams that the SI254 is intended for use with.

Click to Enlarge

Above is the transmission curve for UVFS, with light incident normal to the surface. The data shown is for a 1 mm thick, uncoated sample and includes surface reflections.

Please Give Us Your Feedback

Email		Feedback On
(Optional)
Contact Me:
Your email address will NOT be displayed.

Please type the following key into the field to submit this form:

Click Here if you can not read the security code.
This code is to prevent automated spamming of our site
Thank you for your understanding.

Would this product be useful to you? Little Use 1 2 3 4Very Useful

Enter Comments Below:

Characters remaining 8000

Posted Comments:

Poster: tcohen

Posted Date: 2013-01-02 09:47:00.0

Response from Tim at Thorlabs: Thank you for your request. We may be able to offer a modified SI035 with SIVS to suit your needs. There are manufacturing limits on the shear plate that will restrict the diameter from much smaller than 1mm. As you have not provided an email for us to contact you directly, please contact us at techsupport@thorlabs.com to discuss possible solutions for your beam diameter.

Poster:

Posted Date: 2012-12-19 07:26:57.45

Are there plans to offer plates for beam diameters < 1 mm?

Poster: rscholl

Posted Date: 2012-12-05 11:52:00.0

A response from Ryan at Thorlabs: Thank you for contacting us. It sounds like the issue is regarding the contrast of the stripes or interference fringes. This suggests the coherence length is less than several times the optical path length difference of the interfered beams. We will contact you directly for more information.

Poster: martin.vogel

Posted Date: 2012-11-23 14:35:06.927

Hi, I have a strange observation using the SI100: With a blue laser @ 488nm, I see a nice patterns of stripes. With a yellow laser @ 580nm, I also see a stripe pattern, but it is overlaid with a bright spot of light. Any idea what could be the cause for this? Many thanks, Martin

Poster: tcohen

Posted Date: 2012-09-13 13:09:00.0

Response from Tim at Thorlabs: When using the SI100, we would expect to see about ~2.8mm at your wavelength. You will notice the wedge angle increases for smaller beam diameters to reduce the fringe spacing and be discernible in the visible wavelengths. As the fringe spacing is directly proportional to wavelength, it will be larger for 1.55um. Currently, we are working on NIR shearing interferometers to be able to be detected with the same convenience as our visible versions.

Poster: ron.stahl

Posted Date: 2012-09-07 14:29:54.0

What fringe spacing can I expect from a 1.55micron wavelength beam with the SI100? I found a formula that suggests that it would only be a few microns and I'm concerned that I won't be able to see this with my InGaAs camera.

Poster: david.milne

Posted Date: 2011-08-17 15:19:02.0

Can you explain why you need different shear plates for different beam diameters? For instance if I use a large beam with the small diameter shear plate, will I still see fringes? If I use a small beam with a large diameter shear plate, will I still see fringes?

Poster: jjurado

Posted Date: 2011-08-17 13:51:00.0

Response from Javier at Thorlabs to david.milne: The reason why different plates are offered for different ranges of beam diameters is that, in order to observe the interference pattern of a particular beam generated by the front and back surfaces of the shear plate, the wedge angle of the optic needs to be carefully chosen. Launching a large beam onto a small diameter shear plate (and vice versa) will cause the front and back surface beams to be misaligned, preventing the formation of the interference pattern. I will contact you directly for further support.

Poster: jjurado

Posted Date: 2011-08-02 13:47:00.0

Response from Javier at Thorlabs to dcasale: In order to view the fringe pattern generated by the interferometer at 1064nm, it would be necessary to place a translucent fluorescing material on top of (or in place of) the diffuser plate, or to use an IR viewer or camera. We currently do not carry these product, but I will contact you directly with some suggestions.

Poster: dcasale

Posted Date: 2011-08-01 14:17:19.0

What is recommended when viewing 1064nm lasers? Should the top plat be replaced with a fluorescing material, or can it be laid directly on top/below?

Poster: jjurado

Posted Date: 2011-05-04 15:00:00.0

Response from Javier at Thorlabs to Eric Le Moal: Thank you very much for contacting us. I will contact you directly to help you troubleshoot your application.

Poster: eric.le-moal

Posted Date: 2011-05-04 09:09:45.0

Dear Sir/Madam, the shearing interferometer shows no fringe contrast with our laser source that emits 6 ps pulses at 1064 nm (I use a IR camera to look at the shear plate). As 6 ps pulses are relatively short (1.8 mm in vacuum), I wonder if this is a time coherence issue. Could you please tell me what is the thickness of the shear plate itself? (namely the length difference between the two interfering paths) Best regards, Eric Le Moal

Poster: jjurado

Posted Date: 2011-02-24 14:44:00.0

Response from Javier at Thorlabs to Sebastian Jaeger: Thank you for contacting us. In order to integrate our shearing interferometers into our cage systems, it is necessary to use the SITST plate. The current design does not feature additional holes for the 30 mm cage system.

Poster:

Posted Date: 2011-02-24 05:21:47.0

Dear Sir or Madame, is it possible to mount the shearing interferometer in front of an cage-system (e.g. a 30mm cage system) or do I need to go over a SM1 thread by using the SITST plate? Best regards, Sebastian Jäger

Poster: Thorlabs

Posted Date: 2010-09-14 08:58:33.0

Response from Javier at Thorlabs to Holger Fischer: we will contact you directly in order to troubleshoot your application.

Poster: fischer

Posted Date: 2010-09-09 07:31:12.0

Dear Madame or Sir, we have purchased a shearing interferometer (SI100) to determine the collimation of a laser beam. Unfortunately we are not able to see any fringes on the screen of the assembly. The laser beam is well adjusted at 45° to the shear plate with a diameter of about 6-8mm. Different lasers (pulsed and cw) at different wavelengths (780nm, 532nm and 648nm) did not show any result. Do you have any proposition for getting fringes or any contact to get more information on the shearing interferometers? Best regards, Holger Fischer

Poster: apalmentieri

Posted Date: 2010-02-02 13:58:56.0

A response from Adam at Thorlabs to Nick: The wedge angle for these interferometers are 117 arcsec(SI035), 83 Arcsec(SI050), and 40 Arcsec(SI100).

Poster: nick

Posted Date: 2010-02-02 13:23:52.0

Hello, Can you please tell me the wedge angle in the SI035, SI050, and SI100 plates? This is useful in determining fringes across the 500-2000nm range that might be utilized. Thanks, Nick

Poster: Laurie

Posted Date: 2009-04-06 16:21:18.0

Response from Laurie at Thorlabs to msones: Thank you for your interest in our shearing interferometers. Unfortunately, at this time, we do not have the appropriate measurement equipment necessary to determine the degree of fringe tilt in terms of divergence. We regret that we are unable to help you determine this specification. Please let us know if you have additional questions.

Poster: msones

Posted Date: 2009-03-30 18:09:51.0

I need to know the sensitivity of this product: i.e. how many degrees of fringe tilt correspond to how many microradians of divergence (full angle). Assume wavelength = 635nm. Thank you, Mike

Poster: Laurie

Posted Date: 2008-07-15 16:31:43.0

Response from Laurie at Thorlabs to roedel: Dear Christian Rödel: Thank you for your inquiry about our shearing interferometers. I will be contacting you directly with some additional information about the SI750. The clear aperture is 115 mm and the wedge angle is 7 arcsec. If you should need more information, please dont hesitate to contact us.

Poster: roedel

Posted Date: 2008-07-15 14:59:12.0

Dear Sir or Madam, Id like to purchase a shearing interferometer with 50-75mm beam diameter. We want to use it to align collimation but it should be very sensitive. To calculate it can you please send me the parameters of the shearing plate. So the wedge thickness, aperture and angle should be useful. Thanks in advance, Christian Rödel

Poster: laurie

Posted Date: 2008-05-06 13:49:04.0

Response from Laurie at Thorlabs to nolan.real: If you purhcase the SI035 assembly, youll be able to measure beams ranging in diameter from 1-3 mm. Then, you can use the same subassembly (the plate comes off) and replace it with a SI050P to measure beams from 2.5-5mm. I would highly suggest that you also purchase the SIVS accessory. I have used our shearing interferometers personally for beams in this range, and the SIVS is very helpful for discerning the fringes. Thank you for your interest in our products!

Poster: nolan.real

Posted Date: 2008-05-06 11:24:16.0

trying to measure beams from 1-5mm. Do not understand what combination will allow this. will the si035 be able to measure up to 25.4mm with the different plates?

Poster: Tyler

Posted Date: 2008-03-13 08:33:19.0

Response from Tyler at Thorlabs: Dear tliu, thank you for interest in our product. The wedged plate in the interferometer is made from BK7 glass and as a result will absorb the 230 nm radiation. Please consider contacting our technical support department with your need; they can generate a quote for a custom interferometer made with a UV fused silica wedged plate.

Poster: tliu

Posted Date: 2008-03-13 05:41:03.0

Can this shearing Interferometer used for 230nm UV laser beam?

Click on any phrase below to search our site using our new Search Engine:

accessory beam BP109 VIS check coherent collimate collimated collimation collimation tester collimator detection diffuser examine fringe incident infra infrared interferometer ir kinematic laser laser interferometer plate qualitative red screen shear shear plate sheared shearing shearing accessory shearing interferometer shearing interferometer accessory shearing interferometers test view viewing wavefront wedge

View All »Matching Part Numbers

Shearing Interferometers

Features