Laser Pointer - Colors and Wavelengths

Colors and Wavelengths

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 under 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, more easily visible because of 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. Yellow-orange laser pointers, at 593.5 nm, later became available. In September 2005 handheld blue laser pointers at 473 nm became available. In early 2010 "Blu-ray" (actually violet) laser pointers at 405 nm went on sale.

The apparent brightness of a spot from a laser beam depends on the optical power of the laser, the reflectivity of the surface, and the chromatic response of the human eye. For the same optical power, green laser light 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 stated in milliwatts (mW). In the U.S. lasers are classified by the American National Standards Institute and 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 or IIIb lasers generate between 5 and 500 mW; Class 4 or IV lasers generate more than 500 mW. The US FDA Code of Federal Regulations stipulates that "demonstration laser products" such as pointers must comply with applicable requirements for Class I, IIa, II, or IIIa devices.