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Categories of Laser Pointer

The 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 no greater than 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, 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. In September 2005, handheld blue laser pointers at 473 nm have also become available. Very recently, blu-ray/violet lasers at 405 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 chromatic 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 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 measured in milliwatts (mW). In the US, lasers are classified by the American National Standards Institute and by the 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/IIIb lasers (operating between 5-500 mW) and Class 4/IV lasers (operating above 500 mW) cannot be legally promoted as laser pointers.

Red/red-orange laser pointer

These are the simplest pointers, as laser diodes are available in these wavelengths. The pointer is essentially no more than a battery-powered laser diode. The first red laser pointers were released in the early 1980s; they were large, unwieldy devices sold for hundreds of dollars. Today, they are much smaller and generally cost very little. In recent years diode-pumped solid state red laser pointers emitting at 671 nm have also become available. Although this wavelength can be obtained directly with an inexpensive laser diode, higher beam quality and narrower spectral bandwidth are achieved through DPSS.

Yellow laser pointers

Yellow laser pointers emitting at 593.5 nm have become available to the market in the last few years. Although they are based on the DPSS process, in this case two lasing lines of the ND: YVO4, 1064 nm and 1342 nm, are summed together with a nonlinear crystal. The complexity of this process makes these laser pointers inherently unstable and inefficient, with their outputs ranging from 1 mW to about 10 mW, varying a lot with temperature and usually mode-hopping if they get too hot or too cold. That is because such a complex process may require temperature stabilizers and active cooling, which can't be mounted into a small sized host. Also, smaller 593.5 nm pointers work in pulsed mode so they can use smaller and less powerful pumping diodes.

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Need help on Physics Problem?

A double-slit experiment is performed underwater with a submerged HeNe laser. Suppose that the separation of the slits is 0.0142 cm, while the wavelength of the light in air is 633 nm. The screen is 2.35 m away from the slits. Find the distance along the screen, measured from the centerline, that corresponds to the second bright fringe (m = 2). The index of refraction of water is 1.33.

Wavelength in water,
λ = (1/1.33) * 633 x 10^-9 m = 4.76 x 10^-7 m
Distance of mthe order bright fringe, xm is given by
xmd/D = mλ
=> distance of second order bright frindge
x2 = 2λD/d
= 2*4.76*10^-7*2.35/(0.0142*10^-2) m
= 1.575 x 10^-2 m
= 1.575 cm.

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