A laser pointer or laser pen is a (typically battery-powered) handheld device that uses a laser diode to emit a narrow low-power visible laser beam (i.e. coherent light) to highlight something of interest with a small bright colored spot. The beam may be focused with lenses.
The small width of the beam and the low power of typical laser pointers make the beam itself invisible in a clean atmosphere, only showing a point of light when striking an opaque surface. Laser pointers can project a visible beam via scattering from dust particles or water droplets along the beam path. Higher-power and higher-frequency green or blue lasers may produce a beam visible even in clean air because of Rayleigh scattering from air molecules, especially when viewed in moderately-to-dimly lit conditions. The intensity of such scattering increases when these beams are viewed from angles near the beam axis. Such pointers, particularly in the green-light output range, are used as astronomical object pointers for teaching purposes.
Laser pointers make a potent signaling tool, even in daylight, and are able to produce a bright signal for potential search and rescue vehicles using an inexpensive, small and lightweight device of the type that could be routinely carried in an emergency kit.
There are significant safety concerns with the use of laser pointers. Most jurisdictions have restrictions on lasers above 5 mW. If aimed at a person's eyes, laser pointers can cause temporary visual disturbances or even severe damage to vision. There are reports in the medical literature documenting permanent injury to the macula and the subsequent permanent loss of vision after laser light from a laser pointer was shone at a human's eyes. In rare cases, a dot of light from a red laser pointer may be thought to be due to a laser gunsight. When pointed at aircraft at night, laser pointers may dazzle and distract pilots, and increasingly strict laws have been passed to ban this.
The low-cost availability of infrared (IR) diode laser modules of up to 1000 mW (1 watt) output has created a generation of IR-pumped, frequency doubled, green, blue, and violet diode-pumped solid-state laser pointers with visible power up to 300 mW. Because the invisible IR component in the beams of these visible lasers is difficult to filter out, and also because filtering it contributes extra heat which is difficult to dissipate in a small pocket "laser pointer" package, it is often left as a beam component in cheaper high-power pointers. This invisible IR component causes a degree of extra potential hazard in these devices when pointed at nearby objects and people.
Colors and wavelengths Early laser pointers were helium–neon (HeNe) gas lasers and generated laser radiation at 633 nanometers (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 nm wavelength. Slightly more expensive ones use a red-orange 635 nm diode, more easily visible because of the greater sensitivity of the human eye at 635 nm. Other colors are possible too, with the 532 nm green laser being the most common alternative. Yellow-orange laser pointers, at 593.5 nm, later became available. In September 2005 handheld blue laser pointers at 473 nm became available. In early 2010 "Blu-ray" (actually violet) laser pointers at 405 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 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.Laser Beam and Dot Relative Brightness Comparison by Wavelength. 405nm.com. Retrieved on 8 April 2023.
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 InstituteANSI classification scheme (ANSI Z136.1–1993, American National Standard for Safe Use of Lasers). and Food and Drug Administration (FDA)—see Laser safety#Classification for details. Visible laser pointers (400–700 nm) operating at less than 1 mW power are Class 2 or II, and visible laser pointers operating with 1–5 mW power are Class 3A or IIIa. Class 3B or IIIb lasers generate between 5 and 500 mW; Class 4 or IV lasers generate more than 500 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.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.
ColorWavelength(s) Red 638 nm, 650 nm, 670 nm Orange 593 nm Yellow 589 nm, 593 nm Green 532 nm, 515/520 nm Blue 450 nm, 473 nm, 488 nm Violet 405 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. Today, they are much smaller and less expensive. The most common wavelengths are ca. 638 and 650 nm.
Green
High power (W) Diode Pumped Green Lasers first appeared on the market in 1996 in laser photo-coagulation, once the "green problem" was solved. Much lower power (mW) green laser pointersSam's Laser FAQ: Dissection of Green Laser Pointer . repairfaq.org 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 diodes 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 mW) infrared aluminium gallium arsenide (AlGaAs) laser diode operating at 808 nm. The 808 nm light pumps a neodymium doped crystal, usually neodymium-doped yttrium orthovanadate (Nd:YVO4) or 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 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 2009Green diode lasers a big breakthrough for laser-display tech (i-micronews.com via arstechnica.com). 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, NichiaLASER Diode-NICHIA CORPORATION . nichia.co.jp and OSRAMGreen Laser, Visible Laser – OSRAM Opto Semiconductors. osram-os.com developed and manufactured merchant high-power green laser diodes (515/520 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 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
Blue laser pointers in specific wavelengths such as 473 nm usually have the same basic construction as DPSS green lasers. In 2006 many factories began production of blue laser modules for 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 nm, which is produced by frequency doubling of 946 nm laser radiation from a diode-pumped Nd:YAG or Nd:YVO4 crystal (Nd-doped crystals usually produce a principal wavelength of 1064 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, BBO crystals are used as frequency doublers; for lower powers, KTP is used. The Japanese company Nichia controlled 80% of the blue-laser-diode market in 2006.
Some vendors are now selling collimated diode blue laser pointers with measured powers exceeding 1,500 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 nm blue laser light in optimally configured DPSS modules is typically 10–13%, about half that typical for green lasers (20–30%).
Lasers emitting a violet light beam at 405 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 brighteners in the manufacture of products intended to appear brilliantly 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 nm directly without a frequency doubler, eliminating the possibility of accidental 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 nm blue-violet laser diode modules with an optical power of 250 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.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.
Applications
Pointing
Laser pointers are often used in educational and business presentations and visual demonstrations as an eye-catching pointing device. Laser pointers enhance verbal guidance given to students during surgery. The suggested mechanism of explanation is that the technology enables more precise guidance of location and identification of anatomic structures.
Red laser pointers can be used in almost any indoor or low-light situation where pointing out details by hand may be inconvenient, such as in construction work or interior decorating. Green laser pointers can be used for similar purposes as well as outdoors in daylight or for longer distances.