Lasers are increasingly being used in a variety of workplace settings and their unique properties, physical environments and numerous applications present both direct beam exposure and non-beam hazards. Understanding and controlling hazards associated with laser systems is the responsibility of the designated Laser Safety Officer (LSO) or safety engineer to minimize their potential for causing injury, promote workplace safety and be in compliance with local, state and federal requirements. This overview will acquaint safety engineers with laser operation, hazard evaluation, recommended training, regulatory requirements, workplace safety audits and serve as a resource for developing appropriate engineering, administrative and procedural control measures.
Unlike conventional light sources lasers produce highly collimated, coherent and monochromatic beams of light by the process of light amplification by the stimulated emission of radiation (LASER). Lasers produce light (non-ionizing radiation) that is represented on the electromagnetic spectrum between ultraviolet at 180nm and far infrared at 103 micro m. Visible light is generally considered to be between 400-to-700nm wavelengths. Conditions necessary for stimulated emission of radiation to occur require that energy first be imparted to a suitable collection of atoms, ions or molecules known as an active medium. In typical gas laser systems for example this energy transfer usually results from direct currents passing through or RF signals across the laser tube whereas solid state and tunable liquid dye lasers are usually optically excited using flashlamps or light from other laser sources. Semiconductor lasers with their extremely high electrical efficiencies are essentially P-N junction diodes that emit light as a result of current passing through the device.
As a result of intense pulsed or continuous "pumping" or "excitation" absorbed energy raises the collective energy levels of the active medium well above their atomic ground state to upper level metastable states that have comparatively longer atomic lifetimes. Without the benefit of an outside influence or stimulus these charged atoms, ions or molecules will spontaneously decay and return to lower energy levels randomly emitting acquired energy in the form of photons and/or other radiationless transitions of energy during their downward transitions to atomic ground states.
Under very precise and controlled conditions within a laser cavity where the majority of atoms, ions or molecules within the active medium are charged to higher energy levels (i.e., population inversion) there is a higher probability that stimulated emission of radiation will prevail over spontaneous emission. During active pumping or excitation and while a population inversion exists, photons of emitted light become the stimulus for the premature release of potential energy stored in the highly charged active medium.