[Laser] Digikey IR Laser.

Mon, 1 Dec 2003 13:46:24 -0500

	A "relative" power monator is easy to put together. Just back-bias a
photodiode
and measure the voltage drop across the resistor. See Sam's Laser pages for
more info.
This is good enough for relative comparisions.
	On the subject of CCD cameras: the cheaper ones may be better for IR work
as they do not have an IR blocking filter. The more expensive ones do. If
you are out buying, take an IR LED and battery to test the camera.
	I've been experimenting with IR laser diode from CD players. They're cheap
(free). I'm also interested in cloud bounce/tropo scatter commuications.
Would like to make contest contacts without having to be Line-of-sight.

best to all,
walt, N3EVV

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Andrew T. Flowers, K0SM
Sent: Monday, December 01, 2003 10:46 AM
To: [email protected]
Subject: Re: [Laser] Digikey IR Laser.

David,

I have a couple of those wired up in my expanders and running into a
10mm lens.  I don't have any way to measure output power right now, so
I'm keeping current a bit below I(op) to be safe.  I'm not really
concerned with linearity in my system, but I can tell you that the
active current region for these devices is something like 50-150ma, so
you have alot of room to play.  They don't even come with a feedback PD,
so it's just assumed that you set it and forget it.  I'd like to try
some troposcatter stuff once I get back to Nebraska this month (clear
sky, one farmlight every mile or so) and it would be since to have some
measurement of power output-I don't expect it to be the same at -10C as
it is in my apartment :-) If anyone knows how to get a rough power
measurement with out spending big $$$ I'd like to hear it.

I built my expander out of a few sections of PVC and utilized the 5-10cm
adapter/lens/housing unit that is also on digikey's site.  That seems to
be enough to keep it cool--mind you I'm running it at  a little below
I(op) at 50% duty cycle, but it doesn't really get warm.  Anyway, this
all results in a well collimated "rectangle" of light about 7-8cm long.
 I used my computer's quickcam to do some alignement--I know it's not
optimal, but it's good enough until I can borrow a decent camcorder or
something witha zoom feature.

 I have a schematic of the expander and other laser stuff on my webpage:

http://mail.rochester.edu/~af006m/laser.html

Andy K0SM/2

[email protected] wrote:

>Hi group.
>
>A few months ago someone mentioned the 120mW IR laser available from
digikey
>at $20 (ish)
>
>I was going to order one, but wondered if anyone in the group has used one
of
>these devices and has any practical tips.
>
>e.g.
>What's the supply current to output power response like?
>
>Is the standard brass housing large enough to dissipate the heat from a
120mW
>diode or should I be looking at mounting it in a large heatsink?
>
>It's the first time I'll have used IR.  Does anyone know if a typical
digital
>camera LCD for monitoring my attempts to focus the optics.
>
>Finally, I realise that 120mW is dangerous..........I plan to use a 50mm
dia
>lens with a short focal length to produce a beam that's somewhere between
30
>and 50mm dia. Hopefully this will be a safe level of 'power density'.  If
the
>diode has a divergence of 30 degrees, then a convex lens of about 25mm
focal
>length should do the job.
>Now to find the best material for the wavelength......
>
>Thanks.
>
>If it all works I'll write up the results on my laser pages.
>
>
>David    G0MRF              <A
HREF="www.g0mrf.freeserve.co.uk">www.g0mrf.freeserve.co.uk</A>
>
>
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