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The Wedged Optical Flat is Held in Place with Three Magnets.
These Shearing Interferometers can be used with incident beams as small as Ø1 mm and as large as Ø50 mm depending on which shear plate is used. The interference pattern is sensitive to the beam divergence and can be used to qualitatively determine whether the beam is collimated. As shown in the figure to the right, the plate has three steel balls fixated to the bottom of the plate, which attach magnetically to the base. This magnetic retention mechanism enables easy swapping of plates when different beam diameters are used. Please see the Specs tab for compatible plates and bases.
In addition, there is a hole drilled into the back of the base plate, thus enabling the light that is transmitted through the wedged optical flat to continue unimpeded. For all models except the SI500, this hole is SM1 threaded (1.035"-40). The SI500 output is a Ø2.95" (Ø75 mm) smooth bore. The base plate, diffuser plate, and shear plate come packaged in a carrying case.
Please note that due to the thickness of the shear plate optic in the SI100, SI254, and SI500, the back surface of the shear plate protrudes from the mounting plate as can be seen in the image to the right. Therefore, care should be taken when inserting or removing these plates from the base unit, especially if the SICP or SICPSM1 cage adapter plates are installed.
Thorlabs offers five interchangeable shear plates, which together are designed to be used with incident beam diameters ranging from 1 mm to 50 mm. The magnetically coupled kinematic design of these plates allows them to be precisely located on the shearing interferometer. Multiple plates are compatible with the same base (see the table below for compatibility), thus enabling the plate to be interchanged easily if the beam diameter being used for a particular experiment changes. Different shear plates are offered for different diameter beams due to the optimization of the wedge angle for the beam diameter.
Please note that due to the thickness of the shear plate optic in the SI100P, SI254P, and SI500P, the back surface of the shear plate protrudes from the mounting plate. Therefore, care should be taken when inserting or removing these plates from the base unit, especially if the SICP or SICPSM1 cage adapter plates are installed.
The SIVS accessory is helpful for viewing the fringe pattern created by a small diameter beam. By replacing the standard diffuser plate viewing screen on the SI035, SI050, SI100, or SI254a with this accessory, the size of the fringes will increase, thereby making it easier to determine if the light is collimated. The SIVS comes packaged with two 1/16" screws so that it can be secured to the shearing interferometer.
If desired, the mounting plate for the SIVS can be purchased separately (SITST). It features a standard Thorlabs SM1 (1.035"-40) thread, which is compatible with any of our SM1-threaded components.
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The SICP cage system adapter replaces the diffuser plate included with the shearing interferometer and can be secured using the two 4-40 screws.
These two adapter plates are designed to replace the standard diffuser plate viewing screen on the SI035, SI050, SI100, or SI254 and enable the input side of the shearing interferometer to be attached to a 30 mm cage or SM1 lens tube system. The SICP offers a diffuser for viewing the fringes. The SICPSM1 has an SM1-threaded bore, allowing a Ø1" lens tube such as the one included with the SIVS magnified viewing screen (above) to be attached where the fringes would normally be viewed.
Since these plates feature tapped 4-40 holes for attaching the cage system, the plate cannot be attached to an existing cage system. The ERSCA cage rod adapters will allow this plate to be inserted and removed without having to disassemble the cage system.