How Safe Are Heat Ray Guns? Could a little meddling with the frequencies of the Heat Ray Gun beam result in frying crowds rather than dispersing them? 
 A: Basically, no. I am no fan of the technology, but to answer your specific question, a little meddling with the frequencies should not yield physical damage. Wikipedia has a decent first introduction to dielectric heating by high-frequency electromagnetic radiation. Both deposited power and penetration length depend only weakly on the exact frequency. However, the energy transfer (and potential amount of skin or tissue damage) is directly proportional to the power of the RF wave, so I'd say that's the most direct threat.
A: To pick up from F'x's answer: the frequency has been chosen so it's absorbed very quickly by the skin. This means it is heating only a very thin layer of your skin so it doesn't need very much power to raise the skin temperature.
Suppose you changed the frequency so the radiation penetrated ten times as far into flesh. That means ten times as much flesh is being heated so the temperature increase would be a factor of ten smaller. You'd need to use ten times as much power to get the same temperature increase. That's why F'x says the most direct threat is the power of the beam rather than the exact frequency used.
