Editing Laser pointer (section)

==Colors and wavelengths==
Early laser pointers were [[helium–neon laser|helium–neon (HeNe) gas lasers]] and generated laser radiation at 633 [[nanometer]]s (nm), usually designed to produce a laser beam with an output power under 1 milliwatt (mW). The least expensive laser pointers use a deep-red [[laser diode]] near the 650&nbsp;nm [[wavelength]]. Slightly more expensive ones use a red-orange 635&nbsp;nm diode, more easily visible because of the greater [[luminous efficiency function|sensitivity of the human eye]] at 635&nbsp;nm. Other colors are possible too, with the 532&nbsp;nm green laser being the most common alternative. Yellow-orange laser pointers, at 593.5&nbsp;nm, later became available. In September 2005 handheld blue laser pointers at 473&nbsp;nm became available. In early 2010 "[[Blu-ray]]" (actually violet) laser pointers at 405&nbsp;nm went on sale.

The apparent brightness of a spot from a laser beam depends on the optical power of the laser, the reflectivity of the surface, and the chromatic response of the [[human eye]]. For the same optical power, green laser light will seem brighter than other colors, because the human eye is most sensitive at low light levels in the green region of the spectrum (wavelength 520–570&nbsp;nm). Sensitivity decreases for longer (redder) and shorter (bluer) wavelengths. Additionally, the beam's brightness can be influenced by Rayleigh scattering, as shorter wavelengths such as blue and violet light are scattered more readily in the atmosphere making the beam more visible in the air.<ref>[https://405nm.com/laser-beam-and-dot-relative-brightness-comparison/ Laser Beam and Dot Relative Brightness Comparison by Wavelength]. 405nm.com. Retrieved on 8 April 2023.</ref>

The output power of a laser pointer is usually stated in milliwatts (mW). In the U.S., lasers are classified by the [[American National Standards Institute]]<ref>''ANSI classification scheme'' (ANSI Z136.1–1993, American National Standard for Safe Use of Lasers).</ref> and [[Food and Drug Administration]] (FDA)—see [[Laser safety#Classification]] for details. Visible laser pointers (400–700&nbsp;nm) operating at less than 1&nbsp;mW power are Class 2 or II, and visible laser pointers operating with 1–5&nbsp;mW power are Class 3A or IIIa. Class 3B or IIIb lasers generate between 5 and 500&nbsp;mW; Class 4 or IV lasers generate more than 500&nbsp;mW. The US FDA [[Code of Federal Regulations]] stipulates that "demonstration laser products" such as pointers must comply with applicable requirements for Class I, II, IIIA, IIIB, or IV devices.<ref>[https://web.archive.org/web/20020918110609/http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=1040.11 FDA Code of Federal Regulations Title 21, Subchapter J: Radiological Health, PART 1040 – PERFORMANCE STANDARDS FOR LIGHT-EMITTING PRODUCTS]. Accessdata.fda.gov. Retrieved on 15 October 2011.</ref>

{| class="wikitable"
!Color
!Wavelength(s)
|-
| Red
| 638&nbsp;nm,  650&nbsp;nm, 670&nbsp;nm
|-
| Orange
| 593&nbsp;nm
|-
| Yellow
| 589&nbsp;nm, 593&nbsp;nm
|-
| Green
| 532&nbsp;nm, 515/520&nbsp;nm
|-
| Blue
| 450&nbsp;nm, 473&nbsp;nm, 488&nbsp;nm
|-
| Violet
| 405&nbsp;nm
|}

===Red===
These are the simplest pointers, as laser diodes are available in these wavelengths. The pointer is most common and mostly low-powered.

The first red laser pointers released in the early 1980s were large, unwieldy devices that sold for hundreds of dollars.<ref>{{cite journal|title=Product Guide|date=November 1981|journal=[[Popular Science]]}}</ref> Today, they are much smaller and less expensive. The most common wavelengths are ca. 638 and 650&nbsp;nm.

===Green===
[[File:Greenlasertrails.jpg|thumb|Trails by a 15 mW green laser pointer in a time exposure of a living room at night]]
Green laser pointers<ref>[http://www.repairfaq.org/sam/laserpic/glpdpics.htm Sam's Laser FAQ: Dissection of Green Laser Pointer] {{Webarchive|url=https://web.archive.org/web/20130522190301/http://www.repairfaq.org/sam/laserpic/glpdpics.htm |date=22 May 2013 }}. repairfaq.org</ref> appeared on the market around 2000 and are the most common type of DPSS lasers (also called ''diode-pumped solid-state frequency-doubled'', DPSSFD). They are more complex than standard red laser pointers, because [[laser diode]]s are not commonly available in this wavelength range. The green light is generated through a multi-step process, usually beginning with a high-power (typically 100–300&nbsp;mW) [[infrared]] [[aluminium gallium arsenide]] (AlGaAs) laser diode operating at 808&nbsp;nm. The 808&nbsp;nm light [[laser pumping|pumps]] a neodymium doped crystal, usually [[Nd:YVO4|neodymium-doped yttrium orthovanadate]] (Nd:YVO<sub>4</sub>) or [[yttrium aluminium garnet#Nd:YAG|neodymium-doped yttrium aluminium garnet]] (Nd:YAG), or, less commonly, [[neodymium-doped yttrium lithium fluoride]] (Nd:YLF)), which lases deeper in the infrared at 1064&nbsp;nm. This lasing action is due to an electronic transition in the fluorescent [[neodymium]] ion, Nd(III), which is present in all of these crystals.

Some green lasers operate in pulse or quasi-continuous wave (QCW) mode to reduce cooling problems and prolong battery life.

An announcement in 2009<ref>[https://arstechnica.com/science/news/2009/07/green-diode-lasers-a-big-breakthrough-for-laser-display-tech.ars Green diode lasers a big breakthrough for laser-display tech] (i-micronews.com via arstechnica.com).</ref> of a direct green laser (which does not require doubling) promises much higher efficiencies and could foster the development of new color video projectors.

In 2012, [[Nichia]]<ref>[http://www.nichia.co.jp/en/product/laser.html LASER Diode-NICHIA CORPORATION]. nichia.co.jp</ref> and [[OSRAM]]<ref>[http://www.osram-os.com/osram_os/en/products/product-catalog/laser-diodes/visible-laser/green-laser/index.jsp Green Laser, Visible Laser – OSRAM Opto Semiconductors]. osram-os.com</ref> developed and manufactured merchant high-power green laser diodes (515/520&nbsp;nm), which can emit green laser directly.

Because even a low-powered green laser is visible at night through [[Rayleigh scattering]] from air molecules, this type of pointer is used by astronomers to easily point out stars and constellations. Green laser pointers can come in a variety of different output powers. The 5&nbsp;mW green laser pointers (classes II and IIIa) are the safest to use, and anything more powerful is usually not necessary for pointing purposes, since the beam is still visible in dark lighting conditions.

===Blue===
{{Main|Blue laser}}
Blue laser pointers in specific wavelengths such as 473&nbsp;nm usually have the same basic construction as DPSS green lasers. In 2006 many factories began production of blue laser modules for [[optical disc|mass-storage devices]], and these were used in laser pointers too. These were DPSS-type frequency-doubled devices. They most commonly emit a beam at 473&nbsp;nm, which is produced by frequency doubling of 946&nbsp;nm laser radiation from a diode-pumped [[Nd:YAG]] or [[Nd:YVO4]] crystal (Nd-doped crystals usually produce a principal wavelength of 1064&nbsp;nm, but with the proper reflective coating mirrors can be also made to lase at other "higher harmonic" non-principal neodymium wavelengths). For high output power, [[beta barium borate|BBO]] crystals are used as frequency doublers; for lower powers, [[potassium titanyl phosphate|KTP]] is used. The Japanese company [[Nichia]] controlled 80% of the blue-laser-diode market in 2006.<ref>{{cite news| url=https://www.theguardian.com/technology/2006/sep/14/newmedia.media|work=The Guardian|location=London|title=Is the end in sight for Sony's laser blues?|date=14 September 2006|access-date=7 May 2010|first=Jane|last=Qiu|author-link=Jane Qiu}}</ref>

Some vendors are now selling collimated diode blue laser pointers with measured powers exceeding 1,500&nbsp;mW. However, since the claimed power of "laser pointer" products also includes the IR power (in DPSS technology only) still present in the beam (for reasons discussed below), comparisons on the basis of strictly visual-blue components from DPSS-type lasers remain problematic, and the information is often not available. Because of the higher neodymium harmonic used, and the lower efficiency of frequency-doubling conversion, the fraction of IR power converted to 473&nbsp;nm blue laser light in optimally configured DPSS modules is typically 10–13%, about half that typical for green lasers (20–30%).{{citation needed|date=June 2013}}

Lasers emitting a violet light beam at 405&nbsp;nm may be constructed with GaN ([[gallium nitride]]) semiconductors. This is close to ultraviolet, bordering on the very extreme of human vision, and can cause bright blue [[fluorescence]], and thus a blue rather than violet spot, on many white surfaces, including white clothing, white paper, and projection screens, due to the widespread use of [[optical brightener]]s in the manufacture of products intended to appear brilliantly {{nowrap|white{{hsp}}{{mdash}}}}{{hsp}}the brighteners are chemical compounds that absorb light in the violet (and [[ultraviolet]]) region of the [[electromagnetic spectrum]] and re-emit light in the blue region by fluorescence. On ordinary non-fluorescent materials, and also on fog or dust, the color appears as a shade of deep violet that cannot be reproduced on monitors and print. A GaN laser emits 405&nbsp;nm directly without a frequency doubler, eliminating the possibility of accidental [[#Infrared hazards of DPSS laser pointers|dangerous infrared emission]]. These laser diodes are mass-produced for the reading and writing of data in [[Blu-ray]] drives (although the light emitted by the diodes is not blue, but distinctly violet). In mid-to-late 2011, 405&nbsp;nm blue-violet laser diode modules with an optical power of 250&nbsp;mW, based on GaN violet laser diodes made for Blu-ray disc readers, had reached the market from Chinese sources for prices of about US$60 including delivery.<ref>In September 2011, GaN diode laser modules capable of operating at 250mW (or 300mW pulse) with a heatsink were offered on eBay in the Industrial Lasers category at around US$60.</ref>