6D30.35 - Thin Film Interference - HeNe Laser and Glass Plates or Wedges

Code Number:
Demo Title:
Thin Film Interference - HeNe Laser and Glass Plates or Wedges
Thin Film Interference
Area of Study:
Two Glass Plates separated by a width of tape, Helium-Neon Laser (2 to 5 mw.), Diverging Lenses, Optics bench (in place of Stand and Holder), Concave Mirror, Focusable Laser Pointer.

Screw the lenses onto the laser for a large divergent beam.  Point this at the angled plates.  Observe the reflected patterns on a screen.  The interference patterns can be altered by squeezing the plates together.

NOTE: The optical flat is in 6D30.10  -  Newtons Rings box.

The concave mirror is thin plastic that will have reflections off of the back and front surfaces.  This will produce interference patterns on a screen located at least 3 meters from the mirror.  The laser used for this is a focusable laser.  Change the focus to give the best pattern in the particular room you are in.

  • Michele D'Anna and Tommaso Corridoni, "Thin Film Interference: An Experiment with Microwaves and Paraffin Oil", TPT, Vol. 53, #8, Nov. 2015, p. 475.
  • Thomas B. Greenslade Jr., "From our Files: Laser Interference by Convex Mirror", TPT, Vol. 41, #4, Apr. 2003, p. 250.
  • O-455: "Air Wedge Between Glass", DICK and RAE Physics Demo Notebook.
  • T. Kallard, "Interferometer for Measuring Parallelism and Small Wedge Angles", Exploring Laser Light, p. 120.
  • T. Kallard, "Thin Film Interference Using an Air Wedge", Exploring Laser Light, p. 132.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.