Diode lasers (laser diodes) use nearly microscopic chips of gallium arsenide or other exotic semiconductors to generate coherent light in a very small package. The energy level differences between the conduction and valence band electrons in these semiconductors are what provide the mechanism for laser action. Common features to consider for diode lasers include fiber pigtailed and array configuration.  A laser diode can have an optical fiber pigtail precisely aligned and attached for optimum coupling efficiency.  In an array laser diodes are packaged as multiples.  Laser diode arrays will contain a certain number of elements (diodes). 

Important laser performance parameters to consider when specifying diode lasers include wavelength, beam size, beam divergence, operating current range, operating temperature range, and pulsed.  The wavelength specifies the output wavelength of the laser diode.  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 operating current is the current range the laser diode is designed to operate in.  The operating temperature is the temperature range the laser diode is designed to operate in.  Average power is an important continuous wave laser specification to consider. Average Power is the power (in watts) of a continuous wave laser.  Some diode lasers are designed for pulsed operation.  Important pulsed laser specs to consider include pulse energy, pulse length, and repetition rate.  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.