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 (5 mW) are safe to use, but devices with power of 100 mW or more sold on the Internet have recently caused permanent eye damage.
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 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 because of 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 the green laser pointer, is used as an astronomical-object pointer 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.
Return From Laser Pointer To Telescope Accessories Main Page Telescopes Home Page
Part of this text was taken from Wikipedia and is available under the Creative Commons Attribution-ShareAlike License