[Laser] laser pointer

[Jim Moss]

James,
When using RED it is no problem for the target to see the TX. It is bright and insanely bright when on target.
(at 25-30 miles)

The Green has the advantage that the eye is more sensitive there than red.
Most of the RX setups have very wide relative beamwidths so adding an alignment from the RX won't really do much.

There are other potential advantages to green. 
The frequency control is better. It is based on IR exciting a 1064nM xtal and then a 2x mult to 532nM.
So it is more stable than a 640nM diode. 

If you want big power, remove the xtal & mult and use the IR diode! (but it wont be well controlled frequencywise but it may be better based on propagation of IR thru air vs green.

Jim
N9JIM



----- Original Message ----
From: James Whitfield <n5gui at cox.net>
To: Free Space LASER Communications <laser at mailman.qth.net>
Sent: Tue, April 13, 2010 1:15:39 PM
Subject: [Laser] laser pointer

Recent posting about laser pointers reminded me of a question that I had for 
this group regarding the use of green laser pointers.

I have noticed that amateur some astronomers have mounted green laser 
pointers on their telescopes, presumably to indicate where in the sky the 
telescope is pointing.  Some are in addition to a "finder scope", but some 
seem to be instead of the older technology.  ( Not relevant to 
communications, but I have seen some mounted on computer controled "go to" 
scopes, which have me puzzled -- are they a manual pointing aid when the 
computer is switched off, or are they used to show the point in the sky to 
surrounding observers where the computer has plotted the position of an 
object? )

The green laser pointers show a green line that is much more visible from 
the side than is typical of red laser pointers.  The green laser pointers 
are far more expensive to "tinker" with for communications experiments, and 
many of the common detectors are less sensitive to green than red.  I would 
not consider using them as the communications element.  However, since they 
are much easier to see with the human eye, they seem well suited as 
"pointers" for any light communication device: laser, LED, or particularly 
IR.

I have thought that using such a sighting guide on a light communication 
receiver would make it easier to align the communications equipment in the 
field.  I was wondering if anyone has tried to do this, or even better has 
some suggestions about how to use them.

James
n5gui



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