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How does a green laser pointer work?
(Or: Why are they more expensive than red laser pointers?)

Solid state green lasers are a relatively new item to the
consumer market, but red laser pointers have been around
for some time. While the prices of green laser pointers will
probably drop over time, they will never approach the $5 - 10
range of the cheap red ones.

Most red laser pointers have two basic components, a solid
state diode laser and a collimating lens. There are also drive
electronics that provide a constant drive power to the laser
diode and may provide thermal stability.

Green laser pointers use Diode Pumped Solid State Frequency
Doubling technology. Our laser pointers have a Sony high
power infrared laser diode that generates light at 808nm,
which pumps a crystal of Nd:YVO4 (Neodymium-doped Yttrium
OrthoVanadate). That crystal generates light at 1,064 nm, which
feeds a KTP (Potassium Titanyl Phosphate, KTiOPO4) intracavity
frequency doubler, which produces a green beam at 532 nm.
The green beam then travels thru an output coupler, an
expanding lens, an IR filter to remove unwanted IR from the
beam, then thru a collimating lens and finally exits thru a
glass output window.

There are also drive electronics that are more complex than
those in a red laser pointer. More heat is generated than by a
red laser diode, so there is feedback that keeps the drive
current regulated. And, all of the optical components in the
green laser must be precisely aligned, so there are many more
mechanical parts than in a red laser pointer. The process of
generating a green beam from the IR light from the pump
diode is less effecient than a red laser diode directly emitting
a red beam, so batteries need to be larger to have a reasonable
operating life.

Some green laser pointers generate a pulsed beam to reduce
thermal problems and extend battery life, but new technology
allows a bright continuous beam without eating batteries. The
momentary pushbutton makes sure the laser isn't accidentally
left on.

All of this stuff is housed in a sturdy pen-sized housing that holds
everything in place and protects the innards from the weather
and the operator. Don't try to take the pointer apart as this will
void the warranty, as will removing the serial number sticker.

Battery life depends on usage, but 2-3 hours of on-time during
busy operation can be expected from two AA alkaline cells. Cold
temeratures reduce the performance of the laser and batteries,
so keep the pointer warm at the chilly star parties. The life of the
Sony IR laser diode is about 4,000 hours, or something like 1,600
sets of batteries. The rest of the components will operate unless
they are subjected to significant impact. Treat your laser pointer
like you treat your eyepieces and it will last a lifetime.

The final product of all this technology is a vividly bright green
beam! At night, the beam appears to go all the way to the stars.
When pointing out a faint fuzzy, folks within several yards of the
pointer will clearly see the beam and the place you are pointing.


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