Laser pointer

A laser pointer or laser pen is a small portable and visible laser designed to highlight something of interest by projecting a small bright spot of colored light onto it. Doctors say that laser pointers with power less than 5 milliwatts (5mW) are safe to use, but devices with power of 100 mW or more sold on the Internet have recently caused permanent eye damage. (See laser safety) The small width of the beam and low power of typical laser pointers make the beam itself invisible in a reasonably clean atmosphere, showing a point of light when striking an opaque surface.

Some higher-powered laser pointers project a visible beam via scattering from dust particles or water/fog droplets along the beam path. Higher power and higher frequency lasers (green or blue color) may have a visible beam even in clean air due to 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, in the same general manner as flashlights.

The recent 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 (DPSS) "laser pointers" in green, blue, and violet, of extremely high visible power (100–300 mW). Because the IR in the beams of these lasers is difficult to filter and contributes heat which is difficult to dissipate in a pocket laser pointer package, it is often left as a beam component in cheaper high-power "pointers." This causes a degree of extra potential hazard in these devices.

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. In early 2010 "Blu-ray" (actually violet) laser pointers 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 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 3A or IIIa. Class 3B/IIIb lasers (operating between 5–500 mW) and Class 4/IV lasers (operating above 500 mW) cannot be legally promoted as 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. The first red laser pointers were released in the early 1980s; they were large, unwieldy devices sold for hundreds of dollars.[4] Today, they are much smaller and generally cost very little. In recent years diode-pumped solid state (DPSS) red laser pointers emitting at 671 nm have also become available. Although this wavelength can be obtained directly with an inexpensive laser diode, higher beam quality and narrower spectral bandwidth are achieved through DPSS.

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 the 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-hopping if they get too hot or too cold. That is because such a complex process may require 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.

Green laser pointer

A frequency-doubled green laser pointer, showing internal construction. Cells and electronics lead to a laser head module (see lower diagram) This contains a powerful 808 nm IR diode laser that pumps a Nd:YVO4 laser crystal, that in turn outputs 1064 nm light. This immediately is doubled inside a non-linear KTP crystal, resulting in green light at the half-wavelength of 532 nm. This beam is expanded and infrared-filtered. In inexpensive lasers the IR filter is inadequate, or is omitted.
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 appeared on the market circa 2000, and are the most common type of DPSS lasers (also called DPSSFD for "diode pumped solid state frequency-doubled"). They are 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 808 nm and transmits at 1064 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 (this may be omitted or inadequate in less-expensive "pointer-style" green lasers), 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. 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 of a direct green laser (not requiring doubling) promises much higher efficiencies and could foster the development of new color video projectors.

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 (class llla) 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.
[edit] Blue and violet laser pointers
Main article: Blue laser
Laser trails by a 50mW green laser pointer and a 150mW violet laser pointer.

Blue laser pointers, which became available around 2006, have the same basic construction as DPSS 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 (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 non-principal neodymium wavelengths).

In 2006 many factories began production of blue laser-modules for mass storage devices, and these entered the mass consumer market as laser pointers, as well. There were DPSS type frequency-doubled devices. 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.

Blue lasers can also be fabricated directly with InGaN semiconductors, which produce blue light without frequency-doubling. 450 nm blue laser diodes are currently available on the open market. The devices are brighter than the 405 nm laser diodes, since the longer wavelength is closer to the peak sensitivity of the human eye. Commercial devices like laser projectors have driven down the prices on these diodes, as of March 2010.

Violet lasers may be constructed with GaN (gallium nitride) semiconductors. Gallium nitride lasers emit a violet light beam at 405 nm wave length (close to ultraviolet, bordering on the very extreme of human vision) which can cause bright blue fluorescence (and thus a blue rather than violet spot) on many white surfaces, including white clothing, ordinary white sheet paper with fluorescent brighteners, and projection screens. 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, which means that accidental dangerous ultraviolet emission is impossible. These laser diodes are used in the reading and writing of data in Blu-Ray drives (although the light emitted by the diodes is not blue, but distinctly violet). As of 2010, 50 mW 405 nm violet laser pointers, based on GaN violet laser diodes made for the Blu-ray type disc readers, had reached the market from Chinese sources, for prices of about $40.

At the same time, a few higher-powered (120 mW) 404-405 nm "violet" laser pointers have become available which are not based on GaN, but use DPSS frequency-doubler technology from 1 watt 808 nm GaAlAs infrared diode lasers. As with infrared-driven green laser pointers above, such devices are able to pop balloons and light matches, but this is as a result of an unfiltered high-power infrared component in the beam.[10] See the section on hazards below, for the difficulties with frequency-doubled IR-pumped lasers.

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.

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

Laser pointers are used in a wide range of applications. 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. Also, these green laser pointers are commonly used by astronomers worldwide at star parties or for conducting lectures in astronomy. Astronomy laser pointers are also commonly mounted on telescopes in order to align the telescope to a specific star or location. Laser alignment is much easier than aligning through using the eyepiece.

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.

More recently, laser pointers began to be used in commercial industries. For instance, constructing companies may use high quality laser pointers to enhance the accuracy of showing specific distances, while working on large scale projects. They proved to be useful in this type of business due to their accuracy, which made them significant time-savers.

Laser pointers can also be used in hiking or outdoor activities. Higher powered laser pointers are bright enough to scare away large wild animals which makes them useful for hiking and camping. In these circumstances a laser pointer can also serve as a handy survival tool, as it can be used as a rescue signal in emergencies which is visible to aircraft and other parties, during both day and night conditions, at extreme distances. For example, during the night in August 2010 two men and a boy were rescued from marshland after their red laser pen was spotted by rescue teams.

Routine pointing of lasers at aircraft is illegal in many jurisdictions.
They may also be helpful in medical research in fields such as photonics, chemistry and physics. Laser pointers can be a mean of improving laser therapies or acupuncture therapies.

Entertainment is one of the other applications that have been found for lasers. The most common use of lasers in entertainment can be seen in special effects used in laser shows. Clubs, parties and outdoor concerts all use high-power lasers to dazzle the audience and enhance their visual experience. Laser shows are often extravagant when combining lens, mirrors and smoke.

Hazards

The output of laser pointers available to the general public is limited (and varies by country) in order to prevent accidental damage to the retina of human eyes. Doctors have reported several cases of permanent eye injury from higher-power hand-held devices sold as laser pointers. In the U.K., doctors recommended against laser pointers more powerful than 1 mW.[15][16] In the U.S., regulatory authorities allow lasers up to 5 mW. Swiss doctors reported a case of a boy who bought a 150 mW laser, sold as a "laser pointer," which left him temporarily blind in one eye, and with 20/50 vision in the other eye, after he shined it in a mirror. The boy's vision eventually returned to near-normal. The doctors said that any laser powerful enough to burn holes in paper, light matches or pop balloons are dangerous and could cause immediate blindness. Laser pointers as powerful as 700mW can be bought on the Internet which are indistinguishable from a low-power device.

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. Viewing of a laser pointer beam for more than 10 seconds can be harmful, however.

The UK Health Protection Agency warns against the high-power (over 1 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."
Infrared hazards of DPSS laser pointers

Lasers classified as pointers are intended to have outputs less than 5mW total power (Class 3R). At such power levels, an IR filter for a DPSS laser may not be required as the infrared (IR) output is relatively low and the brightness of the visible wavelength of the laser will cause the eye to react ("blink reflex"). However, higher powered (> 5mW) DPSS-type laser "pointers" have recently become available, usually through sources that do not follow laser safety regulations for laser packaging and labeling. These higher powered lasers are often packaged in the same pointer-style housings as regular laser pointers, and usually lack the IR filters found in professional high-powered DPSS lasers, due to costs and additional efforts needed to accommodate them.

Though the IR from a DPSS laser is less collimated, the typical neodymium-doped crystals in such lasers do produce a true IR laser beam. The eye will usually react to the higher powered visible light; however in higher power DPSS lasers the IR laser output can be significant. What poses a special hazard for this unfiltered IR output is its presence in conjunction with laser safety goggles designed to only block the visible wavelengths of the laser. Red goggles, for example, will block most green light from entering the eyes, but will pass IR light. The reduced light behind the goggles may also cause the pupils to dilate, increasing the hazard to the invisible IR light. Dual-frequency so-called "YAG laser" eye-wear is significantly more expensive than single frequency laser eye-wear, and is often not supplied with unfiltered DPSS "pointer" style lasers, which output 1064 nm IR laser light as well. These potentially hazardous lasers produce little or no visible beam when shown through the eye-wear supplied with them, yet their IR-laser output can still be easily seen when viewed with an IR-sensitive videocamera.

In addition to the safety hazards of unfiltered IR from DPSS lasers, the IR output of unfiltered lasers may also be unscrupulously included in power figures for lasers, including the ability for lasers to burn.

Though green (532 nm) lasers are most common, IR filtering problems may also exist in other DPSS lasers, such as DPSS red (671 nm), yellow (589 nm)and blue (473 nm) lasers. These DPSS laser wavelengths are usually more "exotic", more expensive, and generally manufactured with higher quality components, including filters, unless they are put into "laser pointer" style pocket-pen packages. Most red (635 nm, 660 nm), violet (405 nm) and darker blue (445 nm) lasers are generally built using dedicated laser diodes at the output frequency, not as DPSS lasers. These diode-based visible lasers do not produce IR light.

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 named David Banach was arrested for pointing a green laser pointer at a small jet flying overhead.

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.[27] 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.

In 2009, police in the United Kingdom began tracking the sources of lasers being pointed at helicopters and aircraft using GPS. Police are then dispatched to the address of the attacker, who could face up to five years in prison.

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)[citation needed], 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 began manufacturing similar high powered pointers. The US FDA has published a warning on the dangers of such high powered lasers.[30] 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, citing 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 had yet to determine which classes of laser pointers to ban. 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. In Victoria, New South Wales, and the 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. In Western Australia, regulatory changes have classified laser pointers as controlled weapons and demonstration of a lawful reason for possession is required. The WA state government has also banned as of 2000 the manufacture, sale and possession of laser pointers higher than class 2 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. 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, except for the federal regulation that manufacturers comply with the Radiation Emitting Devices Act. As of November 2008 only two people have 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.

Netherlands
Before 1998, Class 3A was allowed. In 1998, it became illegal to trade Class 2 laser pointers that are "gadgets" (e.g. ball pens, key chains, business gifts, devices that will end up in children's possession, etc.). It is still allowed to trade Class 2 (< style="font-weight: bold;">Sweden

The use of pointers with output power > 5 mW is regulated in public areas and school yards.

United Kingdom

UK and most of Europe are now harmonized on Class 2 (<1 style="font-weight: bold;">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.[44] Also, any laser with class higher than IIIa (more than 5 milliwatts) requires a key-switch interlock and other safety features.

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

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.

In Arizona it is a Class 1 misdemeanor if a person "aims a laser pointer at a police officer if the person intentionally or knowingly directs the beam of light from an operating laser pointer at another person and the person knows or reasonably should know that the other person is a peace officer." (Arizona Revised Statutes §13-1213)

On April 30th, 2010, Clint Jason Brenner, 36, of Prescott, AZ was found guilty of two counts of endangerment, each a class 6 felony, and it was also found that each was a dangerous offense, for pointing a handheld laser pointer at a Arizona Department of Public Safety helicopter responding to a late-night burglary in December of 2009. Brenner faces a minimum of 1.5 years and a maximum of three years in prison for each count.

On November 2, 2009, Dana Christian Welch of Southern California was sentenced to 2.5 years in a federal prison after being found guilty of shining a hand held laser light into the eyes of two different pilots landing Boeing jets at John Wayne Airport.

David Moreno
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