Laser Safety

Your eye is your important sensor, keep it safe!

Laser radiation safety is the safe design, use and implementation of lasers to minimize the risk 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 government regulations. Moderate and high-power lasers are potentially hazardous because they can burn the retina, or even the skin. To control the risk of injury, various specifications, for example 21 Code of Federal Regulations (CFR) Part 1040 in the US and IEC 60825 internationally, define "classes" of laser depending on their power and wavelength. These regulations impose upon manufacturers required safety measures, such as labeling lasers with specific warnings, and wearing laser safety goggles when operating lasers.

The eye focuses visible and near-infrared light onto the retina. A laser beam can be focused to an intensity on the retina which may be up to 200,000 times higher than at the point where the laser beam enters the eye. Most of the light is absorbed by melanin pigments in the pigment epithelium just behind the photoreceptors, and causes burns in the retina. Ultraviolet light with wavelengths shorter than 400 nm tends to be absorbed by lens and 300 nm in the cornea, where it can produce injuries at relatively low powers due to photochemical damage. Infrared light mainly causes thermal damage to the retina at near-infrared wavelengths and to more frontal parts of the eye at longer wavelengths.

Following wavelength ranges and their respective pathological damage e.g. on human tissue or eyes:

• 180–315 nm (UV-B, UV-C): Photokeratitis (inflammation of the cornea, equivalent to sunburn)
• 315–400 nm (UV-A): Photochemical cataract (clouding of the eye lens)
• 400–780 nm (visible): Photochemical damage to the retina, retinal burn
• 780–1400 nm (near-IR): Cataract, retinal burn
• 1.4–3.0 μm (IR): Aqueous flare (protein in the aqueous humour), cataract, corneal burn
• 3.0 μm – 1 mm: Corneal burn

Wikipedia

International laser safety classes and examples of associated laser systems:

Class	Description	Examples
1	(safe) Laser radiation not dangerous under reasonable operating conditions including using optical instruments for viewing. Higher-power lasers can be included if radiation is fully enclosed.	0.2-mW laser diode, enclosed 10-W Nd:YAG laser
1M	(low power) Same as Class 1 but with additional restriction that no optical instruments may be used which could focus radiation.
2	(low power) Laser radiation limited to visible spectral range (400-700 nm) with maximum output power < 1 mW. Due to the blink response, not dangerous for eye in case of limited exposure (up to 0.25 s).	Alignment HeNe lasers, many laser pointers, supermarket scanners
2M	(low power) Same as Class 2 but with additional restriction that no optical instruments may be used. Power may be higher than 1 mW but beam diameter must be large enough to limit intensity to levels which are safe for short-time exposure.
3R	(low power) Laser radiation may be dangerous for the eye with maximum output power < 5 mW (for visible radiation). Blink response of eye protects somewhat but use of optical instruments that could focus radiation is hazardous.	Some laser pointers
3B	(moderate power) Laser radiation dangerous for eye with direct viewing and for the skin under special conditions. Diffuse radiation, e.g., scattered from diffuse surface, is typically harmless. Maximum output power < 500 mW (for visible and non-visible radiation).	100 mW CW frequency doubled Nd:YAG laser
4	(high power) Laser radiation is very dangerous for the eye and for the skin. Even light from diffuse reflections may be hazardous for the eye. The radiation may cause fire or explosions.	40-W Q-switched Nd:YAG laser, 4-kW thin-disk laser in a non-encapsulated setup

Essentials of Laser Safety