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Laser pointer

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A keychain laser pointer.

A laser pointer is a portable, pen-sized laser designed to be held in the hand, and most commonly used to project a point of light to highlight items of interest during a presentation. Most laser pointers have low enough power that the projected beam presents a minimal hazard to eyes for incidental exposure. A beam of light is not in itself visible from the side, but only by light scattered by dust particles; 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 impinging on an opaque surface. Some higher powered laser pointers are faintly visible via Rayleigh[citation needed] scattering when viewed from the side in moderately to dimly lit conditions.

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.

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[1] and by the Food and Drug Administration (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. There are high power pointers operating between 5-500mW (class 3B/IIIb) but these are banned in many countries[citation needed] because they can present a variety of hazards to people through ocular exposure to direct beams. Much higher powers (Class 4/IV) are not allowed for laser pointers.

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.

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[2] 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 heatsink; its 1064 nm output is fed into a crystal of potassium titanyl phosphate (KTP), mounted on a heatsink 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.[3] 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.

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 405nm 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. The Japanese company Nichia controls (in 2006) 80% of the market.[4]

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.

In pointing applications such as these, natural hand tremor may cause unwanted jittery motion of the laser dot. Future laser pointers may solve this problem by stabilizing the laser beam from unwanted hand tremor.[5]

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.[6]

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.

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

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.[7] 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.[8][9] Viewing of a laser pointer beam for more than 10 seconds can be harmful, however.[10][11]

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.[12]

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.[13]

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 hazardous devices soared, many manufacturers (mainly in China) began manufacturing similar high powered pointers. The US FDA has published a warning on the dangers of such high powered lasers.[14] 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.[15] 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 user of a laser can apply for an exemption. [16]

Victoria: Importation, sale, manufacture, possession and use of laser pointers which emit a beam with an accessible emission limit greater than 1mW is prohibited.[17]

Western Australia: Regulatory changes have classified laser pointers as controlled weapons and demonstration of a lawful reason for possession is required.[18]Also The State Government has banned as of 2000 the manufacture, sale and possession of laser pointers higher than class 2.[19]

New South Wales & Australian Capital Territory: The product safety standard for laser pointers prescribes that they must be a Class 1 or a Class 2 laser product.[20][21]

you can have any type

Netherlands

Since 1998, the allowed class for laser pointers has been 2; before 1998, class 3a was allowed.[22]

United Kingdom

UK and most of Europe are now harmonized on Class 2 (<1mW) 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 [23]

United States

Laser pointers are Class II or Class IIIa devices, with output beam power less than 5 milliwatts (<5mW). According to FDA regulations, more powerful lasers may not be sold or promoted as laser pointers.[24] Also, any laser with class higher than IIIa (more than 5 milliwatts) requires a key-switch interlock and other safety features.[25]

All laser products offered in commerce in the US must be registered with the US FDA, regardless of output power.[26]

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.[27]

Warning about high-power laser pointers

The UK Health Protection Agency warns against the high-power 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. [28]

See also

References

  1. ^ ANSI classification scheme (ANSI Z136.1-1993, American National Standard for Safe Use of Lasers)
  2. ^ Sam's Laser FAQ: Dissection of Green Laser Pointer.
  3. ^ Crystal manufacturer's website describing Neodymium Doped Yttrium Orthvanadate
  4. ^ Is the end in sight for Sony's laser blues? | Technology | The Guardian
  5. ^ Laser Pointer Without Hand Tremor Jitter And Shake - Stabilized Laser Pointer, Range Finder
  6. ^ "Laser Toys" by Jackson Galaxy, an article about cat play therapy with emphasis on use of lasers
  7. ^ Robert A.Moses., in Adler's Physiology of the eye clinical application, Robert A.Moses., Ed. (Mosby, 1981) ,chap. 1, pp. 1-15
  8. ^ Martin A. Mainster, Bruce E. Stuck, and Jeremiah Brown, Jr "Assessment of Alleged Retinal Laser Injuries" Arch Ophthalmol, Aug 2004; 122: 1210 - 1217
  9. ^ 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.
  10. ^ Sliney DH, Dennis JE. Safety concerns about laser pointers. J Laser Appl. 1994;6:159-164
  11. ^ Martin A. Mainster, Bruce E. Stuck, and Jeremiah Brown, Jr "Assessment of Alleged Retinal Laser Injuries" Arch Ophthalmol, Aug 2004; 122: 1210 - 1217
  12. ^ UK Health Protection Agency Information Sheet on Laser Pointers
  13. ^ USATODAY.com - More reports of lasers being shot into airplane cockpits
  14. ^ Consumer Safety Alert: Internet Sales of Laser Products
  15. ^ "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)
  16. ^ Official announcement of Australian laser ban
  17. ^ Control of Weapons Regulations 2000 S.R. No. 130/2000 Schedule 2 Number 33
  18. ^ Media Statements - Results
  19. ^ Media Statements - Results
  20. ^ Extract from New South Wales Fair Trading Regulation 2007
  21. ^ Fair Trading (Consumer Product Standards) Regulation 2002
  22. ^ Verbod op verkoop van laserpointers. NVS Nieuws, 1998.
  23. ^ The UK Health Protection Agency's Laser Pointer Infosheet.
  24. ^ An FDA interpretation of its regulatory requirements for laser pointers, explaining the power limits for these products
  25. ^ 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.
  26. ^ U.S. Code of Federal Regulations, 21 CFR 1040.10, Food and Drug Administration regulations for Laser Products
  27. ^ [1]
  28. ^ HPA laser pointer information sheet
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