Laser Pointers

A laser pointer is a product that includes a small, inexpensive laser in a portable, pen-shaped format. Due to their low output, laser pointers do not project a visible beam in normal, clear air - rather, their light is visible as a small point of light where the beam intersects a surface. more...

Laser pointers are used to highlight items of interest at some distance, for example during a presentation.

Types of laser pointer

Most laser pointers use a red laser diode of 670/650 nm wavelength. Slightly more expensive ones use the brighter, red-orange, 635 nm diode, giving them twice the visibility of their 670 nm counterparts due to the greater sensitivity of the human eye to the shorter wavelength. Other colors are possible too, with the 532 nm green laser being of the most common. Recently, yellow-orange laser pointers, at 594 nm, have been made available. While these yellow-orange laser pointers are indeed brighter than the best of the red laser pointers, they are still not as bright as green laser pointers, at 532 nm, when compared watt per watt. Green laser pointers will always appear to be brighter than laser pointers of other colours at similar output power levels, because the human eye is most sensitive in the green area of spectrum.

Although blue mains-powered semiconductor lasers had been available for some years, handheld blue laser pointers became available in September 2005.

The output of a laser (which is an indication of its brightness) is measured in milliwatts (mW). typically in Europe/UK the legal requirement is that a laser pointer output does 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 ones, as there are no direct-injection laser diodes. The green light is generated in an indirect process, using a high-power infrared AlGaAs 300 mW laser diode operating at 808 nm, which pumps a crystal of Nd:YVO4, which lases at 1064 nm and is coated with a dielectric mirror reflecting at 1064 nm and transmitting at 808 nm on the diode side. The crystal is mounted on a copper block, acting as a heatsink; its 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, designed to reflect at 1064 nm and transmit at 532 nm. There is an infrared filter behind the mirror, which 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.

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