L4-22: MIRAGE - LASER AND HOT WIRE

ID Code: L4-22
Purpose: Demonstrate how an optical mirage is created
Description: A laser beam is spread into a horizontal line by a cylindrical lens, and passes over a current-carrying wire aligned along the original laser beam. The hot wire causes the air to have a very strong decreasing temperature gradient a long the central section of the laser light line, so that section bends upward. The bent laser line is displayed on the wall or screen across a long distance (perhaps the width of the room), as seen below.

Upward bending of blue light from the sky as it propagates along sun-heated sand in the desert causes blue light to appear to be coming from the ground, creating the classic illusion of a lake in the desert.

Availability: Available

See the Physics Question of the Week for 3/16/2015 for an example of how this demonstration can be used in class interaction and discussion: lecdem.physics.umd.edu/question-of-the-week-archive.html

A neat video of a temperature-inversion-based mirage in the wild: