Why is laser radiation dangerous?

Powerful lasers can evaporate tissue, metal, or ceramics

The 'light' from powerful lasers can be concentrated to power densities (power per area or watts/cm²) that are high enough to evaporate tissue, metal or ceramics. In the medical field, laser radiation is used to remove tattoos or to cut human tissue. In applications such as these, which require a high power laser, there is a high potential risk of injury.

Because the eyes are sensitive to light, they are at increased risk. In fact, it is possible to cause irreversible ocular damage with just one glance into a direct or reflected laser beam, even at lower power output levels.

Physical background
Wave trains of any given laser radiation have a fixed relation to time and space (coherent) and are all of nearly the same wavelength (monochromatic). Laser light can travel over great distances as a nearly parallel (collimated) beam. This means that the power that can impact an area, such as the eye, is independent of the distance to the radiation source. You may have observed that a laser pointer creates a beam spot that remains about the same size over large distances, unlike a torch light.

If you compare a laser with a light bulb, you will notice several differences.

The light bulb emits light over a very broad spectrum of wavelengths with no specific direction of dispersion. The power of the bulb that can reach the eye decreases with distance because the bulb radiates in all directions (see picture). If a light bulb and a laser both emit 1 W of optical power, and there is a 1 metre distance between our eyes and the light source, then the quantity of light coming into our eyes from the laser would be 100,000 times greater than the light from the bulb (this assumes a normally dilated pupil diameter of 7 mm - i.e. eyes adapted to darkness).

Focusability
In addition to the quantity of light that can hit the eye, the high focusability of the coherent laser light is another danger. While the bulb creates an image on the retina of approximately 100 µm, the laser light is reduced to a spot of just a few micrometers (~ 10 µm) in diameter. A physicist would say that the bulb produces incoherent light. Therefore, the laser light that hits the eye is concentrated on a much smaller spot. The power density (power per area or watts/cm²) resulting from this concentration may be high enough to heat up and quickly destroy any tissue in the focus. Since the fovea (the part of the eye responsible for sharp central vision, located on the retina) also has a size of just a few micrometers, it is possible to lose your eyesight with a hit from a single laser pulse.

This information has been adapted from the LaserVision knowledge base. Laser 2000 is Platinum Partner of LaserVision.