Excimer Lasers

Excimer lasers are rare-gas halide or rare-gas metal vapor lasers emitting in the ultraviolet, that operates on electronic transitions of molecules, up to that point diatomic, whose ground state is essentially repulsive. Excitation may be by E-beam or electric discharge.  Excimer lasers can be one of four main types.  These include ArF (193nm), KrF (248nm), XeCl (308nm), and XeF (351nm).

Important geometry considerations for Excimer lasers include length, width, height, and weight.  Laser performance parameters to consider when searching for Excimer lasers include beam size, beam divergence, pulse energy, pulse length, and repetition rate.  The beam size refers to the largest dimension of the beam when exiting the laser.  The beam divergence refers to the change in beam diameter as a function of distance from the laser.  The pulse energy is the energy per pulse of the laser.  The pulse length is the length in time of a pulse.  The repetition rate is the number of pulses per second.

The Center for Devices and Radiological Health (CDRH), part of the Food and Drug Administration (FDA), has a laser safety classification scheme.  Classes for lasers include Class I, Class II, Class IIa, Class IIIa, Class IIIb, and Class IV.  Class I include lasers that are not hazardous for continuous viewing or are designed in such a way that prevent human access to laser radiation. These consist of low power lasers or higher power embedded lasers (i.e. laser printers).  Class II cover lasers emitting visible light, which because of normal human aversion responses, do not normally present a hazard, but would if viewed directly for extended periods of time (like many conventional light sources).  Class IIa lasers emit visible light not intended for viewing, and under normal operating conditions would not produce an injury to the eye if viewed directly for less than 1000 seconds (i.e., bar code scanners).  Class IIIa lasers normally would not cause injury to the eye if viewed momentarily but would present a hazard if viewed using collecting optics.  Class IIIb covers lasers that present an eye and skin hazard if viewed directly. This includes both intrabeam viewing and specular reflections. Class IIIb lasers do not produce a hazardous diffuse reflection except when viewed at close proximity.  Class IV refers to lasers that present an eye hazard from direct, specular and diffuse reflections. In addition such lasers may be fire hazards and produce skin burns.