Disclaimer:

Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources.

Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA.

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CAUTION:  These are high power lasers.  Extreme care must be taken to insure that they are NEVER pointed at the audience, or more likely, impact the eyes of the lecturer.

The usual solution for the fish tank is to put 2 tablespoons of "Pine-Sol" into the 40 gallons of water that the tank holds.  1/4 bottle of the green fluorescent dye can also be added to enhance the laser beam viewing.  This solution will work with both green and red lasers.

A solution that will work only for red lasers is to put 3 to 4 teaspoons of water soluble Fluorescein into the 40 gallons of water the tank holds. 

The above solutions will only need to be emptied from the tank if the water become dirty of collects too much chalk.  Otherwise, they will remain good for this demonstration for up to a decade.