Laser pointer

From Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2007)

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. Consequently, beams from laser pointers are generally not visible from the side in normal clear air, but only visible as a point of light where the beam strikes a diffusely reflective surface. Some higher powered laser pointers are faintly visible via Rayleigh scattering when viewed from the side in moderately to dimly lit conditions.

[edit] 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. Recently (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 color 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 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 II and visible laser pointers operating with 1-5 mW power are Class IIIa. Class IIIb lasers emit power between 5 mW and 500 mW (0.5 watt) and are not allowed for laser pointers. Class IIIb lasers can present a variety of hazards to personnel through ocular exposure to direct beams.

[edit] 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.

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 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. The output power of most green laser pointers is on the scale of 5 mW.

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.

[edit] 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, although the light is more violet than blue (405nm). In this case, no frequency doubler is needed. The Japanese company Nichia controls (in 2006) 80% of the market.^[4]

[edit] Applications

Laser pointers are often used in school 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 skygazing. 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.

[edit] Hazards

Main articles: Laser safety and Lasers and aviation safety

The output of laser pointers available to the general public is generally limited to 1 mW or 5 mW (varies by country) in order to prevent accidental damage to the retina of human eyes. In 1981 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 "the risk to the human eye from transient exposure to light from commercially available class IIIa laser pointers having powers of 1, 2, and 5 mW seems negligible." In one study, retinas from patients scheduled to have an eye removed were exposed to light from class IIIa laser pointers, caused visible retinopathy in the human eye with exposures in 60 seconds.^[8] Viewing of a laser pointer beam for more than 10 seconds is potentially harmful.^[9]

[edit] Regulations

In the late 1990s, the laser pointer became a fad amongst adolescents as an irritant to be pointed stealthily at a movie theater screen or even at a person's eyes. In January of 2005, a New Jersey man was arrested for pointing a green laser pointer at a small jet flying overhead.^[10]

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 FDA has published a warning on the dangers of such high powered lasers.^[11] 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.

[edit] Australia

Victoria: Importation, sale, manufacture, possession and use of laser pointers which emit a beam with an accessible emission limit greater than 1mW is prohibited.^[12]

Western Australia: Regulatory changes have classified laser pointers as controlled weapons and demonstration of a lawful reason for possession is required.^[13]Also The State Government has banned as of 2000 the manufacture, sale and possession of laser pointers higher than class 2.^[14]

New South Wales & Capital Territory: The product safety standard for laser pointers prescribes that they must be a Class 1 or a Class 2 laser product.^[15][16]

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.^[17]

[edit] Canada

No regulations controlling the importation and sale of laser pointers have been established in Canada to date.

[edit] Netherlands

The allowed class for laser pointers is 3a.^{[citation needed]}

[edit] 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 ^[18]

[edit] United States

Any laser with class higher than IIIa requires key control and other safety features.^[19] All laser products offered in commerce in the US must be registered with the US FDA, regardless of output power.^[20]

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.^[21]

[edit] High-powered portable lasers

In recent years, high-powered portable lasers have come on the market from a number of specialized suppliers and electronics importers. These lasers can exceed several hundred mW in output. Because those are Class IIIb lasers (higher than 5 mW output), they are not true "laser pointers" by common definition, although hobbyists still refer to them as "pointers".

Many Class IIIb portable lasers incorporate safety features and interlocks not found on a standard, low-power laser pointer. These may include a safety dongle and/or safety key, an aperture shutter, a power indicator light, and an emission delay of two or three seconds.

[edit] See also

Electronics Portal

• Pointer (rod)
• Laser safety

[edit] References