6D10.10 - Interference - Laser and Cornell Plate (Db. Slit)

Code Number:
Demo Title:
Interference - Laser and Cornell Plate (Db. Slit)
Diffraction of Waves
Area of Study:
Optics, Astronomy
Helium-Neon Laser (2 to 5 mw.), Optics Bench, Cornell Plate, Razor Blade, and 7 cm Lens.

The slit plate has single, double, and multiple as well as variable slits on it.  With the laser as shown you can show a variety of diffraction and interference patterns.  Information on the plate is in the file.

Two variations of the laser and slit plate demo are as follows.  To easily see what the difference between a single and double slit diffraction pattern look like, shine the laser through the double slit pattern.  Then with a razor blade cover one of the slits.  In this way you can instantly see the difference between the two patterns.

Direct a diffuse laser beam onto the central diffraction pattern.  Using the 7 cm. lens you can focus two different images.  At the focal length you get a row of diffracted dots as if the laser beam was not expanded.  Outside the focal length you get an image of the diffraction pattern that is on the slit plate.

By using the pointer or the variable slit to block one or more of the diffraction nodes out of the transmitted image, the image will at times become more focused and at other times less focused depending on which nodes are blocked.

A simple reproduction of Thomas Young's original experiment is to place a 2 mm piece of note card edgewise into the beam of a laser pointer.  Use the variable focus laser pointer and adjust it to the narrowest beam possible.  You will get a double slit pattern on the screen that can be investigated in a variety of ways.

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