modulated laser

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From: MC elover (mcelover@yahoo.com)
Date: Wed Apr 18 2001 - 21:03:24 PDT 

Message-ID: <20010419040324.15435.qmail@web906.mail.yahoo.com>
Date: Wed, 18 Apr 2001 21:03:24 -0700 (PDT)
From: MC elover <mcelover@yahoo.com>
Subject: modulated laser

Hello

If there have been any responses to my laser diode
question, I haven't read them yet since i only get the
once-a-day pinhole digest. But without any response I
can tell you all that YES, you CAN modulate the
intensity of a laser pointer. I just did it and I was
amazed and perplexed.

Here's what I did -- following the design of a similar
apparatus that used a flashlight instead of a laser
pointer. I first dismantled the pointer a bit to
access the battery terminals. I made a coil of about
200 turns around a nail. I hooked up the coil to the
speaker output of a radio. The coil then went into a
circuit with batteries (i used a power supply at 3
Volts) which I hooked back up to the battery
terminals. Then hit the button and the laser turns
on. Upon looking at the laser dot on a wall ... well,
it looked like any other laser dot.
    Here's the kicker: I set up a solar cell connected
to an amplified speaker. When I shine the laser at
the solar cell ... MUSIC! So the ordinary-looking
laser dot was actually fluctuating in intensity. I
suppose I made a kind of AM radio (or light-wave)
transmitter. But to tell the truth, I'm still a
little fuzzy on how the whole thing works. From the
modulated laser (the fact that it works is still
amazing to me) to the solar cell/amplifier
reproduction of the sound, I feel like I'm not quite
getting the whole story. Any input?

Diodes are weird.

--Eric

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