Safety of Diode Laser

Though  their small size and low input power, diode lasers may still represent a significant hazard to vision. This is especially true where the output is collimated and/or invisible (near IR), and/or higher power than the typical 3 to 5 mW. At least you don’t have to worry about getting zapped by any high voltage (as in a HeNe or argon laser).

One should never look into the beam of any laser - especially if it is collimated. Use an indirect means of determining proper operation such as projecting the beam onto a white card, using an IR detector card or tester (where needed), or laser power meter.

  • Laser diodes in CD players operate at 780 nm (near IR, virtually invisible). While safely tucked away inside the optical pickup, risks are quite minimal because the output is usually less than 1 mW and the emerging beam is highly divergent. However, if modifications are made to the pickup (such as by removing the objective lens), a 5 mW collimated beam may be produced which can burn holes in the retina of your eye without you even being aware there is a problem.
  • Common visible red laser diodes, diode laser modules, and laser pointers produce 1 to 5 mW at various wavelengths between 670 and 635 nm. When collimated (as in the case of a module with internal optics or a laser pointer) the entire beam can enter the eye and burn holes in the retina. Note that light at 635 nm appears more than 5 times as intense as light at 670 nm. Therefore, the apparent brightness of a source is not a reliable indication of its actual optical power output.Currently, green laser pointers are not simple diode lasers but are Diode Pumped Solid State Frequency Doubled (DPSSFD) lasers (this may change in the future, however). For a given power, green appears substantially brighter than red wavelengths but are also limited a maximum power of 5 mW. However, since there is a high power IR laser diode inside a green pointer and not all include an adequate IR-blocking filter, there could be other dangers lurking even if the green output is weak or dead.According to a recent report by Dr. David Sliney, who is one of the leading “gurus” of laser safety, there are no confirmed accidents or injuries caused by laser pointer of 5 milliwatts radiant power or less. There is an awful lot of nonsense and false claims about this. Pointers are extremely bright, can cause visual distraction, afterimages, and other effects, such as headaches, but under most any typical usage condition, DO NOT cause eye injury. Dr. Sliney works for US Army, and has published papers and books on laser safety for over 20 years.

With both of these, the beam from the bare laser diode is highly divergent and therefore less of a hazard since the lens of the eye cannot focus it to a small spot. However, there is still no reason to look into the beam.

  • Writeable optical drives (WORM, CD-R) may use IR laser diodes producing 10s of mW. A typical CD-R drive sets the laser power at 3 to 5 mW for read and 25 to 30 mW for write. Various types of laser cameras and laser typesetters may use laser diodes of 100s of mW. These are extremely dangerous even if not that well collimated. Furthermore, since they also use near-IR wavelengths so that there is essentially no warning that a beam is present. In fact, since the response of the human eye to near-IR radiation results in an weak indication of red light, one may be led to the false conclusion that the output is a weak visible beam when the actual optical power is 10,000 times higher and the damage has already been done.
  • Much higher power visible and IR diode lasers are available and becoming much more common and affordable with the popularity of diode pumped solid state lasers (including green laser pointers which contain a high power IR laser diode). These represent even greater danger to vision and potentially even risk of heat damage or fire from a focused beam.With these high power laser diodes, even the divergent beam from the bare device is a definite hazard at close range. Where there are collimating optics (even an almost invisible microlens), the result is a mostly or totally invisible beam that can be dangerous to vision from direct exposure and specular reflection at distances of several feet. These are particularly scary especially for people who have become complacent about diode laser safety due to their expectation of a widely diverging beam.

For IR laser diodes in particular, especially if you are considering selling a product:

You need to take a close look at the CDRH rules, because there is no blink reflex in the IR. IR diode lasers are considered much more dangerous and therefore are in a higher class. CDRH has a curve of power versus wavelength that is used for determining safety classes. The only way a IR laser gets less then a IIIb rating (read: dangerous) is if the beam is totally enclosed or of very low power. Go to CDRH, call them and request a manufacturers’ packet by mail. It’s huge and confusing, but covers the requirements for products using IR laser diodes such as 3-D scanners, perimeter sensors, and so forth.

http://www.photon-zone.com/photon-theory/the-safety-of-diode-laser.html

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