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Laser pointer

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This is an old revision of this page, as edited by Pmurph5 (talk | contribs) at 11:52, 28 October 2009 (Added "Definition" section. This clarifies that there is no single definition of a "laser pointer", lists factors that may be included in a definition, and gives examples of different definitions). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A keychain laser pointer

A laser pointer is a small laser designed to highlight something of interest by projecting a small bright spot of coloured light onto it. Most laser pointers have low enough power that the projected beam presents a minimal hazard to eyes for incidental exposure. The laser beam is not in itself visible from the side, but is visible as a result of light scattered by dust particles along the beam path. The small width of the beam and low power of typical laser pointers makes the beam itself invisible in a reasonably clean atmosphere, showing a point of light when striking an opaque surface. Some higher powered laser pointers are faintly visible via Rayleigh scattering when viewed from the side in moderately to dimly lit conditions.

Definition

There is no single generally-accepted definition for the term "laser pointer". Different groups and jurisdictions may define "laser pointer" by one or more factors including size, power source (battery vs. mains), output power level, and intended use.

For example, in New South Wales, a laser pointer is "a hand-held battery-operated device, designed or adapted to emit a laser beam, that may be used for the purposes of aiming, targeting or pointing."[1] Australian import regulations omit the battery requirement and the intended use, but specify an output power level: "hand-held articles … designed or adapted to emit a laser beam with an accessible emission level of greater than 1 milliwatt."[2]

Under Food and Drug Administration (FDA) regulations, laser pointers are defined as "hand-held lasers that are promoted for pointing out objects or locations."[3] FDA limits such lasers to hazard Class IIIa: they cannot exceed 5 milliwatts output power in the visible wavelength range. Note that if a hand-held laser is not promoted for pointing purposes, then it may exceed 5 milliwatts and it may be legally sold (as long as it meets all labeling and safety requirements for its hazard class).

To give additional examples of how definitions may vary, Indiana, New York City and Oregon define "laser pointer" broadly as a device that emits laser light visible to the human eye[4][5][6] while Arizona includes the intended purpose: "any device that consists of a high or low powered visible light beam used for aiming, targeting or pointing out features."[7]

Types of laser pointer

The early laser pointers were helium-neon (HeNe) gas lasers and generated laser radiation at 633 nanometer (nm), usually designed to produce a laser beam with an output power no greater than 1 milliwatt (mW). The least expensive laser pointers use a deep red laser diode near the 670/650 nanometers (nm) wavelength. Slightly more expensive ones use a red-orange 635 nm diode, making them more easily visible than their 670 nm counterparts due to 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. In the past few years, yellow-orange laser pointers, at 593.5 nm, have been made available. In September 2005, handheld blue laser pointers at 473 nm have also become available. Very recently, blu-ray/violet lasers at 405 nm have also become available.

The apparent brightness of a spot from a laser beam depends not only on the optical power of the laser and the reflectivity of the surface, but also on the chromatic response of the human eye. For the same optical power, the green laser 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 redder or bluer wavelengths.

The output power of a laser pointer is usually measured in milliwatts (mW). In the US, lasers are classified by the American National Standards Institute[8] and by the FDA. 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 3R or IIIa. Under FDA regulations, Class 3B/IIIb lasers (operating between 5-500 mW) and Class 4/IV lasers (operating above 500 mW) can not be legally promoted as laser pointers.[9]

Red/red-orange laser pointer

These are the simplest pointers, as laser diodes are available in these wavelengths. The pointer is essentially no more than a battery-powered laser diode. The first red laser pointers were released in the early 1980s; they were large, unwieldy devices sold for hundreds of dollars.[10] Today, they are much smaller and generally cost very little. In the last years DPSS red laser pointers emitting at 671 nm have also become available. Although that wavelength can be obtained with an inexpensive laser diode, higher beam quality and narrower spectral bandwidth are achieved through DPSS.

Green laser pointer

A 5 mW green laser pointer directed at a palm tree at night. Note that the beam itself is visible through Rayleigh scattering and airborne dust.
Trails by a 15 mW green laser pointer in a time exposure of a living room at night.

Green laser pointers[11] appeared on the market circa 2000, and are the most common type of DPSS lasers (also called DPSSFD, diode pumped solid state frequency-doubled). They are much more complicated than standard red laser pointers, because laser diodes are not commonly available in this wavelength range. The green light is generated in an indirect process, beginning with a high-power (typically 100-300 mW) infrared AlGaAs laser diode operating at 808 nm. The 808 nm light pumps a crystal of neodymium-doped yttrium aluminum vanadate (Nd:YVO4) (or Nd:YAG or less common Nd:YLF), which lases deeper in the infrared at 1064 nm. The vanadate crystal is coated on the diode side with a dielectric mirror that reflects at 1064 nm and transmits at 808 nm. The crystal is mounted on a copper block, acting as a heat sink; its 1064 nm output is fed into a crystal of potassium titanyl phosphate (KTP), mounted on a heat sink in the laser cavity resonator. The orientation of the crystals must be matched, as they are both anisotropic and the Nd:YVO4 outputs polarized light. This unit acts as a frequency doubler, and halves the wavelength to the desired 532 nm. The resonant cavity is terminated by a dielectric mirror that reflects at 1064 nm and transmits at 532 nm. An infrared filter behind the mirror removes IR radiation from the output beam, and the assembly ends in a collimator lens.

Nd:YVO4 is replacing Nd:YAG and Nd:YLF due to lower dependency on the exact parameters of the pump diode (therefore allowing for higher tolerances), wider absorption band, lower lasing threshold, higher slope efficiency, linear polarization of output light, and single mode output.[12] For frequency doubling of higher power lasers, LBO is used instead of KTP. Newer lasers use a composite Nd:YVO4/KTP crystal instead of two discrete ones.

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

The recent announcement[13] of a direct green laser (not requiring doubling) promises much higher efficiencies and could foster the development of new color video projectors.

Blue laser

Main article: Blue laser

Blue laser pointers, which became available around 2006, have the same basic construction as green lasers. They most commonly lase at 473 nm, which is produced by frequency doubling of 946 nm laser radiation from a diode-pumped Nd:YAG or Nd:YVO4 crystal. For high output power BBO crystals are used as frequency doublers, for lower powers KTP is used.

Blue lasers can also be fabricated with InGaN semiconductors, which emit a blue light beam at 405 nm wave length (close to ultraviolet) which can cause bright blue fluorescence on many white surfaces, including projection screens. On non-fluorescent materials, such as fog or dust, the color appears as a shade of violet that cannot be reproduced on monitors and print. An InGaN laser emits 405 nm directly without a frequency doubler such as 473 and 532 nm lasers, which means that accidental dangerous infrared emission is impossible. These laser diodes are used in the reading and writing of data in Blu-Ray drives. The Japanese company Nichia controlled 80% of the market in 2006.[14]

Yellow laser pointers

Yellow laser pointers emitting at 593.5 nm have become available to the market in the last few years. Although they are based on DPSS process, in this case two lasing lines of the ND:YVO4, 1064 nm and 1342 nm, are summed together with a nonlinear crystal. The complexity of this process makes these laser pointers inherently unstable and inefficient, with their outputs ranging from 1 mW to about 10 mW, varying a lot with temperature and usually mode-hoping if they get too hot or too cold. That's because such a complex process requires temperature stabilizers and active cooling, which can't be mounted into a small sized host. Also, most smaller 593.5 nm pointers work in pulsed mode so they can use smaller and less powerful pumping diodes.

Applications

Laser pointers are often used in educational and business presentations and visual demonstrations as an eye-catching pointing device. 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.

A laser pointer in operation, shown in light and darkness.
Green laser pointing Betelgeuse in Orion.

Laser pointers can be used as toys for pets, especially for cats in play. Some offer a selection of designs for the laser beam to project (e.g. images of butterflies, mice, or flowers), to provide variety. Opinions are divided on the safety of laser pointers used in this way. Some consider laser pointers to be a healthier alternative to the more traditional string for cats because they reduce the risk of choking on the string. Others are concerned that the laser beam may damage pets' eyes, or that the pet will develop frustration problems from not being able to catch the prey.[15]

An accurately aligned laser pointer can be used as a laser gunsight to aim a firearm.

Green laser pointers can also be used for amateur astronomy. On a moonless night, a green laser pointer beam can often be clearly seen, allowing someone to accurately point out individual stars to others nearby.

Some militaries use lasers to mark targets at night for aircraft. This is done to ensure that "friendly" and "enemy" targets are not mistaken. A friendly target may wear an IR emitting device that is only visible to those utilizing night vision (such as pilots.) To pinpoint the exact location of an enemy combatant, they would simply shine a powerful laser beam towards the target, displaying it openly to attack aircraft. This can be one of the most accurate ways of marking enemy targets.[16]

Hazards

Main articles: Laser safety and Lasers and aviation safety

The output of laser pointers available to the general public varies by country in order to prevent accidental damage to the retina of human eyes. The US FDA determined that Class IIIa lasers could cause injury to the eye if viewed directly for approximately 0.25 seconds, although it has cited evidence that exposure to visible lasers is "usually" limited by the blink reflex of the eye, which they have timed at just under 0.25 seconds.[17] More recent studies show that the risk to the human eye from accidental exposure to light from commercially available class IIIa laser pointers having powers up to 5 mW seems rather small, typically involving deliberate staring into the beam for 10 or more seconds.[18][19] Viewing of a laser pointer beam for more than 10 seconds can be harmful, however.[20][21]

The UK Health Protection Agency warns against the high-power (over 5 milliwatt) typically-green laser pointers available over the Internet, with laser beam powers up to a few hundred milliwatts, since they are "extremely dangerous and not suitable for sale to the public."[22]

Regulations and misuse

Since laser pointers became readily available, they have been misused, leading to the development of laws and regulations specifically addressing use of such lasers. Their very long range makes it difficult to find the source of a laser spot. In some circumstances they make people fear they are being targeted by weapons, as they are indistinguishable from dot type laser reticles. The very bright, small spot makes it possible to dazzle and distract drivers and aircraft pilots, and they can be dangerous to sight if aimed at the eyes.

In January 2005, a New Jersey man was arrested for pointing a green laser pointer at a small jet flying overhead.[23]

In 2008, laser pointers were aimed at players' eyes in a number of sport matches worldwide. Olympique Lyonnais was fined by UEFA because of a laser pointer beam aimed by a Lyon fan at Cristiano Ronaldo.[24] In a World Cup final qualifier match held in Riyadh, Saudi Arabia between the home team and the South Korean team, South Korean goalkeeper Lee Woon-Jae was hit in the eye with a green laser beam.[25]

Despite legislation limiting the output of laser pointers in some countries (such as the United States and Australia), higher-power devices are currently produced in other regions (especially China and Hong Kong), and are frequently imported by customers who purchase them directly via internet mail order. The legality of such transactions is not always clear; typically, the lasers are sold as research or OEM devices (which are not subject to the same power restrictions), with a disclaimer that they are not to be used as pointers. DIY videos are also often posted on Internet video sharing sites like YouTube which explain how to make a high-power laser pointer using the diode from an optical disc burner. As the popularity of these devices increased, manufacturers (primarily Chinese) began manufacturing similar high powered pointers. The US FDA has published a warning on the dangers of such high powered lasers.[26] Despite the disclaimers, such lasers are frequently sold in packaging resembling that for laser pointers. Lasers of this type may not include safety features sometimes found on laser modules sold for research purposes.

Australia

In April 2008, following a series of coordinated attacks on passenger jets in Sydney, the Australian government announced that it would restrict the sale and importation of certain laser items. The government has yet to determine which classes of laser pointers to ban.[27] After some debate, Australian government voted to issue a nationwide ban on importing of lasers that emit a beam stronger than 1 mW, which was effective on July 1, 2008. Those whose professions require the use of a laser can apply for an exemption.[28]

In Victoria, New South Wales, and Canberra Australian Capital Territory, a laser pointer with an accessible emission limit greater than 1 mW is classified as a prohibited weapon and any sale of such items must be recorded.[29][30] In Western Australia, regulatory changes have classified laser pointers as controlled weapons and demonstration of a lawful reason for possession is required.[31] Also The State Government has banned as of 2000 the manufacture, sale and possession of laser pointers higher than class 2.[32] In New South Wales and the Australian Capital Territory, the product safety standard for laser pointers prescribes that they must be a Class 1 or a Class 2 laser product.[33][34]

In February 2009, South African cricketer Wayne Parnell had a laser pointer directed at his eyes when attempting to take a catch, which he dropped. He denied that it was a reason for dropping the ball, but despite this the MCG decided to keep an eye out for the laser pointers.

Canada

No regulations controlling the importation and sale of laser pointers have been established in Canada to date,[35] except for the federal regulation that manufacturers comply with the Radiation Emitting Devices Act. As of November 2008 only one person has been charged under the federal Aeronautics Act, which carries a maximum penalty is $100,000 and five years in prison, for attempting to blind a pilot with a laser. Other charges that could be laid include mischief and assault.[36]

Netherlands

Since 1998, the allowed class for laser pointers has been 2; before 1998, class 3a was allowed.[37]

United Kingdom

UK and most of Europe are now harmonized on Class 2 (<1 mW) for General presentation use laser pointers or laser pens. There are no specific UK laws relating to laser pointers; however, Health and Safety regulation insists on use of Class 2 anywhere the public can come in contact with laser light, and the DTI have urged Trading Standards authorities to use their existing powers under the General Product Safety Regulations 2005 to remove lasers above class 2 from the general market [38]

United States

Laser pointers are Class II or Class IIIa devices, with output beam power less than 5 milliwatts (<5 mW). According to U.S. Food and Drug Administration (FDA) regulations, more powerful lasers may not be sold or promoted as laser pointers.[39] Also, any laser with class higher than IIIa (more than 5 milliwatts) requires a key-switch interlock and other safety features.[40]

All laser products offered in commerce in the US must be registered with the FDA, regardless of output power.[41]

In Utah it is a class C misdemeanor to point a laser pointer at a law enforcement officer and is an infraction to point a laser pointer at a moving vehicle.[42]

See also

References

  1. ^ New South Wales: Summary Offences and Law Enforcement Legislation Amendment (Laser Pointers) Bill 2008
  2. ^ Australian Customs Service: Import Controls on Laser Pointers
  3. ^ FDA: Important Information for Laser Pointer Manufacturers
  4. ^ Indiana IC 35-47.4.5 Regulation of Laser Pointers
  5. ^ New York City Administrative Code Section 10-134.2 Regulation of Laser Pointers
  6. ^ Oregon Statues Section 163.709 Unlawful directing of light from a laser pointer
  7. ^ Arizona Statues on aiming a laser pointer
  8. ^ ANSI classification scheme (ANSI Z136.1-1993, American National Standard for Safe Use of Lasers)
  9. ^ FDA: Important Information for Laser Pointer Manufacturers
  10. ^ Product Guide. Popular Science. November, 1981
  11. ^ Sam's Laser FAQ: Dissection of Green Laser Pointer.
  12. ^ Crystal manufacturer's website describing Neodymium Doped Yttrium Orthvanadate
  13. ^ [1] Green diode lasers a big breakthrough for laser-display tech (i-micronews.com via arstechnica.com)
  14. ^ Is the end in sight for Sony's laser blues? | Technology | The Guardian
  15. ^ "Laser Toys" by Jackson Galaxy, an article about cat play therapy with emphasis on use of lasers
  16. ^ Target Marking
  17. ^ Robert A.Moses., in Adler's Physiology of the eye clinical application, Robert A.Moses., Ed. (Mosby, 1981) ,chap. 1, pp. 1-15
  18. ^ Martin A. Mainster, Bruce E. Stuck, and Jeremiah Brown, Jr "Assessment of Alleged Retinal Laser Injuries" Arch Ophthalmol, Aug 2004; 122: 1210 - 1217
  19. ^ Dennis M. Robertson, MD; Jay W. McLaren, PhD; Diva R. Salomao, MD; Thomas P. Link, CRA, "Retinopathy From a Green Laser Pointer ," A Clinicopathologic Study, Arch Ophthalmol. 2005;123:629-633.
  20. ^ Sliney DH, Dennis JE. Safety concerns about laser pointers. J Laser Appl. 1994;6:159-164
  21. ^ Martin A. Mainster, Bruce E. Stuck, and Jeremiah Brown, Jr "Assessment of Alleged Retinal Laser Injuries" Arch Ophthalmol, Aug 2004; 122: 1210 - 1217
  22. ^ UK Health Protection Agency Information Sheet on Laser Pointers
  23. ^ USATODAY.com - More reports of lasers being shot into airplane cockpits
  24. ^ blog.wired.com – Laser Zap Leads to Soccer Fine
  25. ^ kfa.or.kr/sportalkorea – 사우디 관중, 이운재에 레이저 포인터 공격 (includes a photograph showing a laser beam shining upon the goalkeeper's face)
  26. ^ Consumer Safety Alert: Internet Sales of Laser Products
  27. ^ "Laser pointers restricted after attacks". Sydney Morning Herald. 2008-04-06. Retrieved 2008-04-06. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  28. ^ Official announcement of Australian laser ban
  29. ^ Control of Weapons Regulations 2000 S.R. No. 130/2000 Schedule 2 Number 33
  30. ^ [2]
  31. ^ Media Statements - Results
  32. ^ Media Statements - Results
  33. ^ Extract from New South Wales Fair Trading Regulation 2007
  34. ^ Fair Trading (Consumer Product Standards) Regulation 2002
  35. ^ Health Concerns of Hand Held Laser Pointers- RPS
  36. ^ http://www.mytelus.com/ncp_news/article.en.do?pn=regional/alberta&articleID=3035834
  37. ^ Verbod op verkoop van laserpointers. NVS Nieuws, 1998.
  38. ^ The UK Health Protection Agency's Laser Pointer Infosheet.
  39. ^ An FDA interpretation of its regulatory requirements for laser pointers, explaining the power limits for these products
  40. ^ U.S. Code of Federal Regulations, 21 CFR 1040.10(f), Food and Drug Administration regulations for Laser Products. Note that these regulations pre-date the availability of Laser Pointers and so do not reference them by name.
  41. ^ U.S. Code of Federal Regulations, 21 CFR 1040.10, Food and Drug Administration regulations for Laser Products
  42. ^ Utah State Legislature 76-10-2501 Unlawful use of a laser pointer Most states now have similar laws to Utah's making some uses of laser pointers (such as aiming it at police officer or an aircraft (federal law) a crime)
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