Dipartimento di Fisica

PREMISE
The laser (Light Amplification by Stimulated Emission of Radiation) is a source of intense, coherent and directional electromagnetic radiation that can be ultraviolet (200 - 400 nm), visible (400 - 700 nm), or infrared (700 nm - 300 mm).
The risks associated with the use of lasers are both those related to the intrinsic characteristics of the beam, and those arising from equipment that allow to create and maintain this type of radiation. The direct interaction with the beam particularly affects the eyes and skin; for example, the radiation coming from a laser focuses on the retina in an extremely small image, so much so that the incident exposure is increased by almost 5 orders of magnitude, due to the effect of focusing the retina itself.
Even without this effect, of course, some types of lasers produce a sufficiently intense radiation to cause skin burns in case of direct contact. It should also be borne in mind that a laser requires a power supply, with all the consequent dangers associated with high power equipment. Often the active material is in a gaseous state, therefore more difficult to control than solid bars, and it is not always chemically inert or harmless. Sometimes dyes (dye lasers) and therefore solvents are used, and so on.
This brief reminder of things that are certainly known may seem trivial, but it wants to draw attention to aspects that, precisely because they are well known and always under the eyes, can be taken for granted and, therefore, ignored in the procedures of normal operation; this is an extremely dangerous attitude; if on the one hand it is good to acquire the familiarity and manual skills that allow you to carry out technical work safely, it is nevertheless essential not to take anything for granted.

DEFINITION AND CLASSIFICATION
The basis of laser operation is the quantum process of stimulated emission, which can be achieved in different ways, from different materials, with different geometries, and with different wavelengths of emitted radiation. There are therefore many types of lasers, which can be classified starting from:
type of operation (pulsed or continuous wave)
beam wavelength
beam power
The standards consider equipment falling into classes 1 and 2 as devices that can also be used for educational and entertainment purposes without the supervision of experienced personnel. However, the standard recommends that the class 2 laser beam should not be intentionally aimed at people.

New classification.
The new classification consists of seven classes

Class 1 - Lasers considered safe.
Class 1M - lasers emitting in the wavelength range between 302.5 nm and 4000 nm with power not exceeding 1mW. They are safe under normal operating conditions, but can be dangerous if the user uses optical instruments within the beam.
Class 2 - Lasers emitting visible radiation in the wavelength range between 400 and 700 nm, with a power not exceeding 1mW, for which eye protection is normally ensured by defensive reactions such as eyelid reflection, including the use of optical instruments for direct vision of the beam.
Class 2M - Lasers that emit visible radiation in the wavelength range between 400 and 700 nm, with a power not exceeding 1mW, for which the protection of the eye is normally ensured by the defense reaction, including the eyelid reflex. Observation can be dangerous with optical instruments for direct vision of the beam.
Class 3A - Lasers operating in the visible with optical power up to 5 mW, for which direct observation of the laser beam with the aid of amplification optics such as binoculars and telescopes can be dangerous. Accidental observation with the naked eye is not harmful due to the eyelid reflex.
Class 3B - Laser, with optical power up to 500 mW, dangerous in case of direct vision of the beam. Diffuse reflections are normally safe. A laser safety officer must be appointed to be responsible for compliance with precautionary measures.
Class 3R - Lasers that emit in the wavelength range between 302.5 and 106nm, with optical power up to 5 mW, for which direct vision of the beam is potentially dangerous, but the risk is lower than that of class 3B lasers.
Class 4 - Lasers capable of producing dangerous diffuse reflections. These lasers can cause injury to the eyes, skin and fire hazard. Their use requires extreme caution. They require a safety officer.

Old classification.
The old classification consisted of five classes:
Class 1 - Lasers that are safe under reasonably foreseeable operating conditions.
Class 2 - Lasers that emit visible radiation in the wavelength range between 400 and 700 nm; eye protection is normally provided by defensive reactions including the eyelid reflex.
Class 3A - Lasers that are safe for naked eye vision. For lasers emitting in the wavelength range between 400 and 700 nm, eye protection is provided by defensive reactions including the eyelid reflex; for other wavelengths, the risk to the naked eye is no greater than that of Class 1. Direct vision of the Class 3A laser beam with optical instruments (e.g. binoculars, telescopes, microscopes) can be dangerous.
Class 3B - Direct vision of the beam of these lasers is always hazardous; the vision of diffuse reflections is normally not hazardous.
Class 4 - Lasers that are also capable of producing dangerous diffuse reflections; they can cause skin damage and could also present a fire hazard. Their use requires extreme caution.