Bursting Balloon

absorption/reflection of colors - heating effect of radiation - color

What it shows:
Blue light is absorbed by a red filter or object, but reflected by a blue one. If the blue light is supplied by a high powered laser and the filters are blue and red balloons, the heating effect of absorption takes its toll on the red balloon.

How it works:
This demo utilizes the ability of a laser to focus its energy onto a very small area. An argon laser produces blue light, which will be absorbed by a red balloon with an intensity enough (see comments) to melt the balloon and so burst it. You can approach the balloon bursting in various ways:

1. Mount a blue balloon on the pole, show that the laser has no effect, then replace it with the red balloon.
2. Place the red balloon inside a clear, and burst just the red one!
3. Place a blue helium filled balloon inside the red. When the red is burst, the blue is released and floats to heaven!

Setting it up:
To allow time for a localized area of the surface to become sufficiently hot however, the balloon does need to be kept very still. Attach 1   the balloon to a 2m meter stick erected a few rows back into the audience (or about 3m from the laser), or to the side wall of the lecture hall. 2m up in the air also puts the powerful laser light above everyone's head. Use the 125mW argon lasertot with 7x beam expander. 2   The laser should be focused down onto the balloon before the lecture. Use low power for focusing and binoculars to view the focused spot for best results (otherwise it's a two person job to tweak the focus and check the progress).

Comments:
Your ability to burst a balloon obviously depends upon the lasers available to you. It can be tough with 125mW, so we must be pushing the low end, so anything higher than 125mW is going to be easier. Safety considerations are described with the laser in Tools of the Trade. When buying balloons, make sure the red ones are very opaque! Rating ***

1 use double stick foam tapetot
2 Spindler & Hoyer Cat. No. 038659 Spindler & Hoyer inc. Milford, MA 01757