The term LASER stands for Light by Amplification Stimulated Emission of Radiation; that is, light amplification obtained from the process of forced emission of radiation. This process gives the laser beam two important qualities: coherence and monochromaticity.
The laser beam is a "light" beam with a defined color, sent in a defined and identified direction in space. The practical result is the ability to perform efficient work with a laser beam which cannot be performed (or is very difficult to do) with other light sources. When passing laser light through an optical lens, the rays passing through it are focused into a spot with a very small diameter onto a target located at the focal plane of the lens. The density of power (or energy) of the ray on the target is directly proportional to the power (or energy) of the light ray passing through the lens, and inversely proportional to the square of the focal diameter. Therefore, all components of the laser beam, having the same wavelength and lens impact angle, will be focused on the focal length defined for the lens. The practical result is that the focused power density will be much higher than what can be achieved from other light sources.
Energy density and laser beam power
One of the features that distinguishes the laser beam from other light sources is its ability to emit extremely high power density (or energy). This feature is effectively applied to cutting materials, but it also makes the laser beam dangerous in the event of contact with the human body, especially the eyes.
The power density expresses the intensity of the power supply, and is measured in units of watts per square centimeter (W/cm2). A nominal 10 W laser beam can be focused into a tiny dot, only 0.2 mm in diameter, with a massive power density of 3∙104 W/cm2. Pulsed lasers can easily reach a power density (peak power within the pulse) in the range of 109 W/cm2 and even higher.
The nature of the laser beam
Laser radiation, in all its forms, belongs in the sphere of electromagnetic radiation, where the electric field and magnetic field propagate when they are coupled and orthogonal.
The laser systems with relevant applications produce radiation in the optical spectrum, including ultraviolet radiation, infrared radiation and the visible spectrum between them.
Ultraviolet (UV) radiation has the shortest wavelengths in the optical spectrum, from 400nm (near ultraviolet) to 10nm (deep ultraviolet).
Wavelengths in the visible spectrum range from 400nm (purple) to 700nm (red).
In the infrared spectrum, the wavelengths are longer, ranging from 700nm (near infrared) to 1mm (the limit of distant infrared).
The basic energy unit in the optical spectrum can be expressed via a light particle that is called a photon. The photon carries an energy value (a basic "radiation packet") that depends on its specific frequency (f).
This energy value (Ep) can be calculated by the following equation: Ep = h·f = h(c/l)
Where h represents the value 6.626x10-27 erg∙sec, known as the Planck constant (named after the physicist Max Planck).
The significance of this connection is that the energy contained in a photon increases as the photon’s oscillation frequency (f) increases. Similarly, it can be said that a photon’s energy increases as the wavelength (l) decreases. Photons in the ultraviolet range carry the most energy in the optical spectrum, and therefore, like IR light, pose serious potential risks requiring that safeguards be taken.