Laser Issues

About LASER
LASER is an acronym and stands for Light Amplification by Stimulated Emission Radiation. Atoms of a crystal or gas contained in the device are stimulated by focused light waves leading to their amplification and concentration, eventually being emitted in narrow, very intense beams.

Specific features:
 * Very small beam divergence
 * Extremely high radiance
 * Monochromatic short pulses
 * High power

Injury & Absorption
Retina injury occurs only with 380–1400 nm wavelengths (where absorption occurs). The highest absorption occurs between the 400-800nm range. According to the power density flux (S), there is a maximum permissible exposure time (seconds) with the beam. A graph depicts this relationship. Exposure longer than this time is considered to cause damage.

where S – power flux density (W/m2), P – Power (W), r – radius of the eye aperture (m)

For example, permissible exposure time for a power flux density of 25 W/m2 is 0.25s.

Some laser pointers in the market have power flux density up to 5000 W/m2. That would give a maximum permissible exposure time of less than 10-6 seconds.

Green laser is most dangerous, as its not absorbed by the eye, so it causes retinal damage. Blindness! Cause you don’t have time to close your eyes in time, and the laser acts very fast. Kids using green lasers can potentially blind pilots in airplanes. Laser could cause thermal damage for example on the skin. The hazard can be reduced by:
 * 1) lowering the aperture, or
 * 2) changing the beam direction

LASER Types

 * Gas lasers
 * Helium-Neon Laser: holography, spectroscopy, presentation (pointers), barcode scanning
 * Argon laser: Used for coagulation, i.e. surgery. Ophthalmitic surgery, confocal microscopy, retinal phototherapy for diabetes
 * CO2 laser: Used to excise tissue. Ophthalmitic surgery. Cutting and welding material.
 * Chemical lasers: hydrogen fluoride laser, deuterium fluoride laser. Used in scientific research, weaponry. They are usually much more powerful than gas lasers (can reach mega watt values)
 * Dye lasers: dyes such as rhodamine, coumarin. They are used in medicine, spectroscopy, research.
 * Metal-vapor lasers: copper vapor laser is used in dermatology and high-speed photography.
 * Solid-state lasers: ruby laser is used in holography, tattoo removal. It was the first visible-light laser invented (1960).
 * Semiconductor lasers: Aluminium gallium indium phosphide (AlGaInP) laser is used for reading compact discs.