PURPOSE: Show Shlieren image of a candle flame using TV.

DESCRIPTION: A Schlieren image optical system is set up as per the sketch below. The laser beam is expanded using a 40X beam expander and a razor edge is positioned at the focal point of the 12.7 cm focal length projection lens so that it cuts off part of the focus of the laser beam. Lens L2 casts an image of the razor edge onto a nearby screen (not seen at right in photograph). With the razor edge removed, a fine wire mesh is positioned about 5 to 10 cm in front of the first lens such that the lens combination casts an image of the mesh on the same screen. Remove the mesh and install a candle such that the flame lies along the optic axis of the laser beam. Move the razor edge in so that it cuts off most of the direct laser beam and the Schlieren image of the candle flame is visible on the screen. Then remove the screen, install the two crossed polaroids and the TV camera. Adjust the zoom and the focus on the camera to focus the Schlieren image of the candle flame. Rotate the polaroids to adjust the overall brightness of the image.

SUGGESTIONS: This one is nice for use with large groups.


EQUIPMENT: Laser cart with 40X beam expander, candle, fine wire mesh, 12.7cm projection lens, razor edge on double cross carriage positioner, 5cm focal length convex lens, crossed polaroids for decreasing light intensity, and TV camera with zoom lens.

SETUP TIME: 20 min.

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