Sky Pointers

When mounted to a telescope, the Sky Pointers functions as a wonderful finder with unique advantages. For information on it.

The Sky Pointers green laser pointer is a new variation of an old idea that amateur astronomers have practiced for many years : a narrow-beam high power flashlight has been used to point out celestial objects. Tiny particles of dust, pollen, and moisture scatter back enough light from the beam to produce a visible line in the air. If the beam extends far enough, a designated location on the sky can be unambiguously pointed out. Nowadays, with increasing interest in science and astronomy education, and the growth of astronomy clubs and star parties, the Sky Pointers provides a convenient and practical way to show and teach celestial geography.

Red laser pointers have grown cheap and ubiquitous, but unfortunately, they are not very effective as sky pointers. In contrast, green laser pointers are very effective because of the eye's greater sensitivity to the 532 nanometer green light. Under dark sky conditions, the beam from a 5 milliwatt green laser pointer creates a dramatic impression, and the beam apparently extends for more than a kilometer. Any bright light source, ranging from light pollution induced sky glow to a crescent moon, will reduce the apparent brightness of the Sky Pointers although the beam will usually remain visible. The light pollution acts in such a way that people closer to you will still see the beam, whereas those further away may have difficulty.

The reason for the high price of green pointers as compared with red lies in their additional internal complexity. They use a battery powered laser diode controlled by a miniaturized circuit, 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 of 808nm. The infrared laser output is focused into to a small crystal of Neodymium doped Yttrium ortho Vanadate (NdYVO4), which then lases at a longer wavelength of 1064nm. The 1064nm output beam is absorbed in an adjacent crystal of Potassium Titanyl Phosphate (KTP) which resonates at twice the pump light frequency to produce an output of 532nm green laser light. A multilayer interference filter removes residual infra-red light, and the output is focused and collimated into a thin parallel beam. Both of the crystals are artificially grown, and must be cut, polished, and multi-coated to very small tolerances. Only a handful of companies are producing these crystals now.


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