Editing Diode-pumped solid-state laser (section)

== Common DPSSL processes ==
[[File:YAG2.svg|thumb|300px|Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1,064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source. Selection of 946 nm transition light is possible, as well]]
The most common DPSSL in use is the 532&nbsp;nm [[wavelength]] '''green''' [[laser pointer]]. A powerful (>200 [[milliwatt|mW]]) 808&nbsp;nm wavelength [[infrared]] [[GaAlAs]] laser diode pumps a neodymium-doped [[yttrium aluminium garnet]] (Nd:YAG) or a [[neodymium-doped yttrium orthovanadate]] (Nd:YVO<sub>4</sub>) crystal which produces 1064&nbsp;nm wavelength light from the main spectral transition of [[neodymium]] ion. This light is then ''frequency doubled'' using a [[nonlinear optics|nonlinear optical]] process in a [[potassium titanyl phosphate|KTP]] crystal, producing 532&nbsp;nm light. Green DPSSLs are usually around 20% efficient, although some lasers can reach up to 35% efficiency. In other words, a green DPSSL using a 2.5 W pump diode would be expected to output around 500-900&nbsp;mW of 532&nbsp;nm light.

In optimal conditions, Nd:YVO<sub>4</sub> has a conversion efficiency of 60%,<ref>{{cite web|url=http://www.unitedcrystals.com/YVO4Prop.html|title=Nd:YVO4 Properties|website=www.unitedcrystals.com}}</ref> while KTP has a conversion efficiency of 80%.<ref>{{cite web|url=http://www.unitedcrystals.com/KTPProp.html|title=KTP Properties|website=www.unitedcrystals.com}}</ref> In other words, a green DPSSL can theoretically have an overall efficiency of 48%.

In the realm of very high output powers, the KTP crystal becomes susceptible to optical damage. Thus, high-power DPSSLs generally have a larger beam diameter, as the 1064&nbsp;nm laser is expanded before it reaches the KTP crystal, reducing the irradiance from the infrared light. In order to maintain a lower beam diameter, a crystal with a higher damage threshold, such as [[lithium triborate]] (LBO), is used instead.

'''Blue''' DPSSLs use a nearly identical process, except that the 808&nbsp;nm light is being converted by an Nd:YAG crystal to 946&nbsp;nm light (selecting this non-principal spectral line of neodymium in the same Nd-doped crystals), which is then frequency-doubled to 473&nbsp;nm by a [[beta barium borate]] (BBO) crystal or LBO crystal. Because of the lower gain for the materials, blue lasers are relatively weak, and are only around 3-5% efficient. In the late 2000s, it was discovered that [[bismuth triborate]] (BiBO) crystals were more efficient than BBO or LBO for second harmonic generation in mode-locked lasers and do not have the disadvantage of being [[hygroscopy|hygroscopic]],<ref name=redop>{{cite web|url=http://www.redoptronics.com/BIBO-crystal.html|title=BIBO Crystal for Blue Laser|website=www.redoptronics.com}}</ref> which degrades the crystal if it is exposed to moisture. In continuous-wave laser applications, however, BiBO may exhibit instabilities which degrade its performance.<ref>{{Cite journal |last1=Ruseva |first1=Valentina |last2=Hald |first2=Jan |date=2004-06-01 |title=Generation of UV light by frequency doubling in BIBO |url=https://linkinghub.elsevier.com/retrieve/pii/S0030401804002986 |journal=Optics Communications |language=en |volume=236 |issue=1–3 |pages=219–223 |doi=10.1016/j.optcom.2004.03.033|bibcode=2004OptCo.236..219R |url-access=subscription }}</ref>

'''Yellow''' DPSSLs use an even more complicated process: An 808&nbsp;nm pump diode is used to generate 1,064&nbsp;nm and 1,342&nbsp;nm light, which are summed in parallel to become 593.5&nbsp;nm. Due to their complexity, most yellow DPSSLs are only around 1% efficient, and usually more expensive per unit of power.

Another method is to generate 1,064 and 1,319&nbsp;nm light, which are summed to 589&nbsp;nm.<ref name=aip75>{{Cite web |url=http://jap.aip.org/resource/1/japiau/v75/i12/p8240_s1?isAuthorized=no |title=589 nm light generation by intracavity mixing in a Nd:YAG laser &#124; Browse Journal - Journal of Applied Physics |access-date=2010-11-17 |archive-url=https://web.archive.org/web/20110722192236/http://jap.aip.org/resource/1/japiau/v75/i12/p8240_s1?isAuthorized=no |archive-date=2011-07-22 |url-status=dead }}</ref> This process is more efficient, with about 3% of the pump diode's power being converted to yellow light.<ref>Yellow lasers with 2.5 W pump diodes have reached up to around 80 mW</ref>