Laser Pointers

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. more...

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Most laser pointers have low enough 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 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 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 appeared on the market circa 2000, 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 100-300 mW) infrared AlGaAs laser diode operating at 808 nm. The 808 nm light pumps a crystal of Neodymium-doped Vanadate, 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. 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 common green laser pointers is on the order of 5mW.

Read more at Wikipedia.org