Laser Safty

Laser safety is the avoidance of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to official regulations.

A person exposed to laser radiation (especially invisible radiation) may be unaware that damage is occurring. Some lasers are so powerful that even the diffuse reflection from a surface can be hazardous to the eye. Laser radiation predominantly causes eye injury via thermal effects on the retina. A transient increase of only 10 °C can destroy retinal photoreceptors.

The coherence, the low divergence angle of laser light and the focusing mechanism of the eye means that laser light can be concentrated into an extremely small spot on the retina. If the laser is sufficiently powerful, permanent damage can occur within a fraction of a second, faster than the blink of an eye. Sufficiently powerful visible to near infrared laser radiation (400-1400 nm) will penetrate the eyeball and may cause heating of the retina, whereas exposure to laser radiation with wavelengths less than 400 nm and greater than 1400 nm are largely absorbed by the cornea and lens, leading to the development of cataracts or burn injuries.

Infrared lasers are particularly hazardous, since the body's protective "blink reflex" response is triggered only by visible light. For example, some people exposed to high power Nd:YAG laser emitting invisible 1064 nm radiation, may not feel pain or notice immediate damage to their eyesight. A pop or click noise emanating from the eyeball may be the only indication that retinal damage has occurred i.e. the retina was heated to over 100 °C resulting in localized explosive boiling accompanied by the immediate creation of a permanent blind spot.

Since 1990 there have been 400 incidences of lasers directed at aircraft within the United States. Laser aviation safety concerns have led to an inquiry in the US congress. Exposure to hand-held laser light under such circumstances may seem trivial given the brevity of exposure, the large distances involved and beam spread of up to several metres. However, laser exposure may create dangerous conditions such as flash blindness. If this occurs during a critical moment in aircraft operation, the aircraft may be endangered. In addition, some 18 to 35% of the population possess the autosomal dominant genetic trait, Photic Sneeze, that causes the affected individual to experience an involuntary sneezing fit when exposed to a sudden flash of light. Some observers believe that the danger is greatly exaggerated, at least for small hand-held lasers.

Collected From Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Laser_safety

Posted on : 2008-7-24　【Return】