Features

Beam Collimation Information Available for Beams with
Ø1 - Ø40 mm
Magnetically Coupled Kinematic Design Allows Shear Plates
to be Interchanged Precisely
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.

The diffuser plate is used to view the interference fringes created by a coherent beam of light incident at an angle of 45° with respect to the normal of the optical flat (see the images below). 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. For each member of the SI series, the thickness and degree to which the optical flat is wedged is chosen such that 4-6 fringes will be seen on the diffuser plate.

N-BK7 Transmission Curve

Above is the transmission curve for N-BK7, a RoHS-compliant form of BK7. The data is shown for a 1 mm thick, uncoated sample and includes surface reflections.

Converging	Collimated	Diverging

The base is constructed from anodized aluminum, and the plate with the wedged optical flat is held in place magnetically so that it can be easily swapped out for a plate with a different wedged optical flat. Behind the wedged optical flat, a hole is bored through the base to allow the transmitted beam to pass through the optical flat unimpeded. The shearing interferometer has one 8-32 and one M4 threaded mounting hole on the bottom of the base as well as on each of the two sides (i.e., 6 holes total of which 3 are imperial and 3 are metric). The Specs Tab summarizes the compatibility between bases and plates and also lists the thread type associated with each item in the series.

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 1-10 mm.

Item #	Wedge Angle	Included Plate*	Compatible Plates	Compatible Accessories	Threaded Mounting Holes	Dimensions (L x W x H) (mm)
SI035	117 arcsec	SI035P	SI035P, SI050P, SI100P, and SI254P	SIVS, SITST^†	#8-32 and M4	50.8 x 48.3 x 55.9
SI050	83 arcsec	SI050P	SI035P, SI050P, SI100P, and SI254P	SIVS, SITST^†	#8-32 and M4	50.8 x 48.3 x 55.9
SI100	40 arcsec	SI100P	SI035P, SI050P, SI100P, and SI254P	SIVS, SITST^†	#8-32 and M4	50.8 x 48.3 x 55.9
SI254	18 arcsec	SI254P	SI035P, SI050P, SI100P, and SI254P	–	#8-32 and M4	50.8 x 48.3 x 55.9
SI500	10 arcsec	SI500P	SI500P	–	1/4"-20 and M6	116.8 x 133.4 x 134.6

* The wedged plates are made from N-BK7
^† Mechanical Dimensions: Ø30.5 mm x 50.0 mm

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Posted Comments:
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?