Fluore-what?

     If you have read my previous posts, you know the basics of laser operation.  As usual, you can always get more information at the Wikipedia Laser page.  Now let me tell you about a neat phenomenon about certain materials called fluorescence.  When light hits a fluorescent material, the material can shine a different color.  This happens because the light that hits the material excites the atoms.  These excited atoms then release their pent up energy by releasing a different color of light than first hit the material.  The light produced is closer to the red side of what we can see as opposed to the violet side (remember ROYGBIV.  Take a look at About Physics for more info on the visible light spectrum).  You can think of the excited atoms as balls rolling up and down hills, a metaphor I use in my post “Can I make a laser from a flashlight?”  I demonstrate the wonder of fluorescence by using my violet laser pointer to excite various fluorescent materials, which glow a different color in the picture below:

Pretty cool, huh?  Fluorescence is the process that causes objects to light up under black lights.  So next time you go to a rave, you can tell all your friends there exactly why your bleached-white t-shirt and highlighters light up.