Re: Laser Diodes

Ian Wright wrote:

> From: "Ian Wright" <Ian@...>
>
> Hi,
>
> ----- Original Message -----
> From: Brian Bartholomew <bb@...>
> > Somebody is producing measuring devices, based on the Doppler effect
> I
> > think, which use the cheaper laser diodes. The resolution was
> midway
> > in resolution between glass scales and interometry. The price was
> > still a couple $thou per axis, but it might go down with competition
>
> I don't suppose you have any references for this kind of system do
> you? I
> have just come back from a short holiday in Majorca (a Spanish island
> in the
> Mediterranean) and I was amazed to find that the 'pocket laser'
> pointers are
> now selling there for only the equivalent of 3 UKP (about $5).
> Needless to
> say I bought a few to play with and I've just been pulling one to bits
> to
> see what is inside - there is just a laser diode in a gold plated can
> - 3
> wire connection but only two used -

There is an intensity sensing diode there, that's what the 3rd wire is
for.

> and a small plastic convex lens (why is
> this needed?).

The beam from a diode laser expands through a wide angle, more in one
axis
than the other, giving an elliptical beam shape. Shine the laser on a
target
without the lens, and you'll see why the lens is there.

> Connection to the laser diode is direct from the 3 mercury
> batteries via a simple push button switch and so I assume that the
> diode
> incorporates current control within itself.

It doesn't, they use the series resistance of the batteries (and the
laser)
to limit current. Expect shot life with these lasers.

> The light output is, of course,
> red and is powerful for me to see it hitting buildings a couple of
> hundred
> yards away in the dark.
>
> Now I just have to find a good reason for having bought them!!!

I suspect there could be many good uses in the shop.

Jon