Editing Laser diode (section)

=== Electrical and optical pumping ===
Laser diodes form a subset of the larger classification of semiconductor ''p''–''n'' junction diodes. Forward electrical bias across the laser diode causes the two species of [[charge carrier]] – [[electron hole|holes]] and [[electron]]s – to be ''injected'' from opposite sides of the PIN junction into the depletion region. Holes are injected from the ''p''-doped into the undoped (i) semiconductor, and electrons vice versa. (A [[depletion zone|depletion region]], devoid of any charge carriers, forms as a result of the difference in electrical potential between ''n''- and ''p''-type semiconductors wherever they are in physical contact.) Due to the use of charge injection in powering most diode lasers, this class of lasers is sometimes termed ''injection lasers'', or ''injection laser diodes'' (ILD). As diode lasers are semiconductor devices, they may also be classified as semiconductor lasers. Either designation distinguishes diode lasers from [[solid-state laser]]s.

Another method of powering some diode lasers is the use of [[optical pumping]]. Optically pumped semiconductor lasers (OPSL) use a III-V semiconductor chip as the gain medium, and another laser (often another diode laser) as the pump source. OPSLs offer several advantages over ILDs, particularly in wavelength selection and lack of interference from internal electrode structures.<ref>Arrigoni, M. et al. (2009-09-28) [http://www.laserfocusworld.com/articles/2009/09/optically-pumped-semiconductor-lasers-green-opsls-poised-to-enter-scientific-pump-laser-market.html "Optically Pumped Semiconductor Lasers: Green OPSLs poised to enter scientific pump-laser market"], ''[[Laser Focus World]]''</ref><ref>[http://www.repairfaq.org/sam/laserdio.htm#dioopsl "Optically Pumped Semiconductor Laser (OPSL)"], Sam's Laser FAQs.</ref> A further advantage of OPSLs is invariance of the beam parameters – divergence, shape, and pointing – as pump power (and hence output power) is varied, even over a 10:1 output power ratio.<ref>[https://www.photonics.com/WhitePaper.aspx?WPID=1695 Coherent white paper (2018-05). "Advantages of Optically Pumped Semiconductor Lasers – Invariant Beam Properties"]</ref>