The SkyPointer green laser pointer is a new application of an old idea that amateur astronomers have used for many years at star parties: a narrow-beam high power flashlight was used to point out celestial objects. Tiny particles of dust, pollen and water droplets scatter back enough light from a bright beam to produce a visible line in the air. If the line is long enough, there is no ambiguity as to the designated location on the sky.
Nowadays, with increasing interest in astronomy and science education, and the growth of astronomy clubs and star parties, the SkyPointer provides a convenient and practical way for those with a knowledge of celestial geography to show and teach it.
Why Green? Red laser pointers have grown in popularity and fallen in price, but unfortunately, they are not very effective as sky pointers. Green laser pointers however, are very effective, mostly due to the greater sensitivity of the human eye to the 532nm green laser wavelength. Under dark sky conditions, the beam from a 5 milliwatt green laser pointer creates a dramatic impression, and the beam apparently extends for hundreds of meters. Any bright source of light, from light pollution induced sky glow to the Crescent Moon, will attenuate the apparent brightness of the SkyPointer,although it usually will remain visible. The effect of light pollution acts in such a way that people closer to you will still see the beam, whereas those further away may have difficulty.
Construction One of the reasons for the relatively high price of green pointers, as compared with the red ones, lies in the additional complexity of it's construction. It uses a laser diode, driven and controlled by additional circuitry, just like the red ones; however, the diode uses about five times the power of the red ones, and emits it's laser light at an invisible, infrared wavelength. This infrared beam then pumps energy into a small non-linear optical crystal, which lases at twice the pump light frequency (half the wavelength, if you prefer)/ The crystal (of Nd:YVO4) is artificially grown at high temperature, cut, polished, and multi-coated to very small tolerances. Only a handful of companies are producing these crystals now.
Glatter has obtained the highest quality, lowest priced, green pointers on the market. They are constructed of thick stainless steel tubing with a strong pocket clip. The laser power output is guaranteed between 3 and 5 milliwatts, typically 4mw. Some other companies have advertised this output as "5 mw.", so be careful when you compare.
When the SkyPointer is on, the beam pulses on and off at about 1000 Hz. or at about a 75% duty cycle. Because of this when the beam is moving slowly it appears continuous; but when the beam is quickly swept then it produces beautiful dotted lines.
The SkyPointer is powered by two AAA alkaline cells. They work very hard when the pointer is on, supplying about 250 ma. The theoretical pointer on time would be two hours at low average drain, but if used frequently, with long on times, the battery lifetime will be considerably less. SkyPointer is furnished with one set of batteries, in a hinged black metal presentation case. These devices should be treated carefully, and not dropped or banged around. They are warranted against defects for ninety days.
Momemtary, not constant All green class IIIa pointers sold are designed for momentary use in pointer service. This means that they cannot be kept on continuously, and should be on for periods of no longer than one minute. After being on this long, the pointer must be allowed to recover thermally for a similar period. If the pointer is kept on longer, or continuously, it may dim out, however, it will not be damaged because the control circuit will automatically reduce the current.
Safety Precautions must be followed when using the SkyPointer The beam should never be allowed to enter the eye. Although complete permanent blindness will not occur with a momentary, glancing exposure, permanent visual damage may occur if the beam is allowed to enter the eye and fall upon the same area of the retina for more than about 1/4 second. This would be an unlikely occurrence, given that we have an aversion and blink reflex, however, all precautions should always be followed to avoid direct eye exposure.
The SkyPointer should never be pointed at land, water, or aircraft - even distant ones.
When others are observing then the SkyPointer should only be used with permission, and not be pointed at nearby reflective objects as the brilliant reflections will interfere with dark adapted vision. Perhaps surprisingly, the beam in air does not seem to impact dark adaptation much.
The SkyPointer should not be used when others are imaging, as a sweep of the beam through the field may spoil the exposure.
To insure that the previous precautions are followed, the SkyPointer should not be used by unsupervised children.