Everyday Scientist

laser safety

July 31, 2006 at 1:22 pm | sam | lab safety

The Moerner lab had its annual laser-safety training (by W.E.), which is always interesting and exciting. I’ve calculated some safety parameters for one of the lasers I use: an Ar-ion laser operating at 11 W. First, it is important to know the minimum permissible exposure (MPE), or the amount of laser energy your eyes may receive without being damaged. This is deterimed by the color of the source and the viewing time. With visible light, assuming an exposure time equal to the blink response, the MPE = 2.1×10^-3 W/cm².

I can now use the MPE to determine safe viewing distances of intra-beam and diffuse reflections (e.g. off a card). The region where is it unsafe to view the beam—i.e. where you will exceed the MPE—is called the nominal hazard zone (NHZ). For intra-beam viewing, the NHZ = 2 km, so you have to be over 2 km away to be able to look directly in the beam for the time it takes you to blink. Our lab isn’t that big. To view the beam within the lab, you would need goggles with OD > 5 to avoid damage. Cool!

As for diffuse reflections, the NHZ is 40 cm. So if you hold the card at arms length, you should be ok. But use goggles, anyway!

The equations for all these calculations are found in the appendix in the American National Standards Institute book on laser safety. Have fun!