PURPOSE: To demonstrate how a laser cavity works.
DESCRIPTION: The laser beam enters the cavity through a hole in the mirror nearest the laser. The mounts are then adjusted to reflect the laser beam back and forth between the two mirrors. Using curved mirrors with long focal length the beam is seen to walk around the mirrors in an elliptical path. Use vapor from blowing across liquid nitrogen or a very small amount of chalk dust to make the beam visible.
REFERENCES: (PIRA unknown.) See Demonstration Reference File for an interesting article which discusses laser cavities using this idea.
EQUIPMENT: Laser on laser cart, two 30" focal length telescope mirrors.
SETUP TIME: 5 min.
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