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A laser pointer is a type of portable pen-shaped laser normally designed to be held by hand. Laser pointers are most commonly used to project a point of light that can highlight items of interest, for example during a presentation. Most laser pointers have such a low output beam power (less than or about one milliwatt) that they do not project a beam visible from the side in normal clear air, but their light is only visible as a point of light where the beam intersects a diffusely reflective surface. Some high-powered laser pointers emit a beam of light visible from the side in moderately to dimly lit conditions via Rayleigh scattering.
Types of laser pointer
Most inexpensive laser pointers use a deep red laser diode near 670/650 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. Recently, yellow-orange laser pointers, at 594 nm, have been made available. Very recently (September 2005), handheld blue laser pointers at 473 nm have 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 in the green area of spectrum (for low light levels), with sensitivity decreasing as colors become redder or bluer.
The output power of a laser pointer is measured in milliwatts (mW). Typically in Europe/UK the legal requirement is that a laser pointer output not exceed 1 mW; in USA this output is limited to 5 mW for presentation lasers. Lasers with outputs over 5 mW need to be registered with the FDA in the USA.
Green laser pointer
Green laser pointers, the most common DPSS lasers (also called DPSSFD, diode pumped solid state frequency-doubled), are much more complicated than the standard red laser pointers, since 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 200-300 mW) infrared AlGaAs laser diode operating at 808 nm. The 808 nm light pumps a crystal of YVO4, 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 KTiOPO4 (KTP), mounted on a heatsink in the laser cavity resonator. 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 orientation of the crystals must be matched, as they are both anisotropic and the Nd:YVO4 outputs polarized light.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.
See also Sam's Laser FAQ: Dissection of Green Laser Pointer.
Blue laser
Blue DPSS lasers, recently made available by some vendors, have the same basic construction as green lasers. They most often lase at 473 nm, which is produced by frequency doubling of 946 nm laser radiation produced by diode-pumped YAG crystal.Purple laser
Purple DPSS lasers, are currently being developed in Northern Russia, and are constructed very differently than are the green and blue lasers. They most often lase at 415 nm. When sold to the public the prices may vary from $200,000 - $500,000Applications
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 for almost any indoor or low-light situation that needs pointing out details which may be inconvenient to point out by hand, such as in construction work or interior decorating. Green laser pointers can be used, for similar purposes, outdoors in daylight or for longer distances.
Laser pointers may also be affixed to pistols and carbines as an aiming aid - in this application the device is called a laser sight.
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.
Hazards
Like all lasers, laser pointers should never be projected directly into the eyes of a person or animal or indeed any moving vehicle in which the driver or pilot could be distracted. The output of laser pointers is generally limited to 1mW or 5mW in order to protect accidental damage to the retina of human eyes, as lasers with such low output levels are unlikely to cause any damage. There is some debate about whether outputs of 5mW may damage eyes if viewed through spectacles or contact lenses. The Food and Drug Administration (FDA) has determined that Class 3a 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.
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, dangerously, a person's eyes. During late 2004 a man was arrested in USA under terrorist laws when he was identified as pointing a high power green laser pointer into the cockpit of an airplane Presumably in response to such incidents, the USA recently made it a Federal offense to point a laser at an aircraft punishable by up to 5 years in prison. [http://thomas.loc.gov/cgi-bin/cpquery/z?cp109:hr250: USA Lasers ACT 2005
Despite legislation limiting the output of laser pointers in some countries (such as the USA), higher-power devices are currently produced in other regions (especially China), 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. 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.
As powerful handheld green lasers become more popular in today's market, it has become known that irresponsible use of higher powered green lasers can be disastrous. Experts say that a direct shot to the eye from a laser over 15 mW can permanently damage the eye within a fraction of a second. The risk becomes greater with more powerful lasers, which are readily available on the internet today.
The use of safety goggles when operating high-powered lasers is highly recommended.
Retailers of high-powered green laser pointers
In addition to lower powered lasers for business use (~5 mW), several online stores sell higher powered models, ranging from the standard 5 mW to extremely powerful 300 mW models.
A list of high-power laser retailers:
See also
External links
"Laser pointer"