Re: Seeing/sensing the direction a laser beam in the air

On Aug 18, 11:51 am, Albert Goodwill <albertgoodw...@xxxxxxxxx> wrote:
Hello,

Many green lasers (even relatively low-power ones) are visible in the
air, especially in the dark.
However we can not see the red laser with the same power. (I think
this is something about the sensitivity of human eye to different
wavelengths.)

Imagine on top of a small hill or on top of a high-rise building, we
are shining a laser beam (preferably a low power laser IR or some
other wavelength), parallel to the ground (ie pointing to horizon) in
an arbitrary direction (say to the North). The idea is to be able to
"see" (or sens) this laser beam from the ground as a direction
indicator (like a compass), even if we are far away (few kilometers)
from the source of the laser.

My question is that with what type of sensor (may be some sort of very
sensitive camera) we can see/sens the laser beam (its direction) in
the air both in the day time and in the dark?

I could imagine that the visibility of the laser beam would be
function of the "density" of the air (dust particles, humidity etc.),
wavelength and laser power.

Can you elaborate on how to built a laser system to indicate an
arbitrary direction?

Thx.

Albert

If you ever been in the situation where you doubt if the batteries in
a remote control was emty , then next time use a digital camera one
with a small view screen then you do not even need to take a picture,
most of these see Ir as white , try it it is a handy trick to
reconise Ir. btw.

.

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