Respecting High Power Lasers

Written by Tom Nugent on Friday, January 30th, 2009

A couple of years ago, we noted the effects of intense laser beams on beam stops such as foamed carbon. In that post, we used a 1kW laser at low power, only a couple hundred watts if memory serves. It was also less than one meter from the target, and was on for less than a minute. Yet we still oxidized the carbon, which was evident before seeing the burn mark – it was glowing slightly orange with the laser on.

Last weekend we took our new 2kW+ laser and fired it near full power. It was above 50% power (we ramped up slowly from 50% to ~90%) for nearly five minutes. This time, the target was roughly 7 meters away, and the beam at the target was roughly 2 inches by 8 inches. Not only did we still oxidize the carbon, but we fried off some surface layers of carbon and then wound up cracking the block all the way through! You could still feel the heat coming off the back side of the block a couple of minutes later. Here’s what the block looked like a few seconds after we turned off the laser:

Yes, it’s still glowing red hot (the small red dot is our alignment laser pointer). And here’s a close-up a few minutes later, showing the oxidation damage as well as the crack (we’re pretty sure it was thermal stress that cracked the block):

These images just reinforce that the level of power we’re using for power beaming is beyond “just” eye danger and well into the realm of immediate skin danger – at the peak in the center of the beam, the power density was probably greater than 300 normal solar intensity. Our lasers from 2006 were powerful but the brightness was not as high as the new laser. Dilas has done an impressive job in increasing the brightness of the laser, and as a result the beam is much better collimated, so it stays very intense over a much longer distance. That is part of what enables us to beam adequate power over a kilometer away. It is also why so many safety precautions need to be taken in order to beam power outdoors (e.g., for the Beam Power competition).