US: UPDATED - Danger of infrared light from some green laser pointers

Some green laser pointers may be emitting dangerous levels of invisible infrared light, in addition to the visible green light, according to a U.S. government agency. The National Institute of Standards and Technology purchased three low-cost 10 mW pointers and found that “one unit emitted dim green light but delivered infrared levels of nearly 20 mW -- powerful enough to cause retinal damage”. Tests by a second NIST team “found similarly intense infrared emissions in some but not all units.”

The NIST team came up with a simple “home test” so that interested persons can test their own laser pointers. The test requires a digital or cellphone camera, a compact disc used to spread out the wavelengths, a webcam to view infrared light, and an infrared TV remote control.

At top, light from a green laser pointer is diffracted (spread out) by a compact disc and viewed with a digital camera that can see only visible light. At bottom, a webcam with no infrared-blocking filter shows this laser also emits infrared laser light (white dots). For this unit, the invisible infrared light is more powerful than the visible green light. (NIST photo)

The unwanted and potentially hazardous infrared light is due to misaligned or missing filters in laser pointers that use infrared to generate visible green light. Low-cost pointers are at special risk, due to cutting corners in design, materials or manufacture to reduce costs.

The team warns that, whether or not a laser pointer emits dangerous levels of infrared, users should “never point the lasers at the eyes or aim them at surfaces such as windows which can reflect infrared light [as well as visible light] back to the user” or others in the area.

For more information:

• NIST press release summarizing the issue

• NIST technical note A Green Laser Pointer Hazard which includes instructions on how to test to see if a green laser pointer has unwanted or excess infrared light emission (PDF format)

UPDATE - March 2011: A laser expert has privately warned LaserPointerSafety.com that the CD technique requires caution. This is because when the laser light is diffracted, the infrared light is no longer co-linear (same path) as the visible light. Therefore, the viewer cannot know exactly where the IR light is going unless they are looking through an IR-sensitive camera or webcam.

Tags: NIST, Infrared laser, Photo