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'[EE]: "Lasers again" distance measurement'
2001\02\02@111157 by Robert Francisco

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Another way of measuring distance is to shoot a laser to a mirror( on a
taget)  and have the reflected beam 'interfere' with a ref beam. You can get
very high resolutions. Basically counting the destructive/constructive waves
of the laser.

Robertf

{Original Message removed}

2001\02\03@064745 by mike

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On Fri, 2 Feb 2001 10:09:25 -0600, you wrote:

>Another way of measuring distance is to shoot a laser to a mirror( on a
>taget)  and have the reflected beam 'interfere' with a ref beam. You can get
>very high resolutions. Basically counting the destructive/constructive waves
>of the laser.
Probably not much use for tractor-sized distances, but it does remind
me of a really fun demo...
Many He-Ne lasers have a rear mirror that lets some light pass (i.e.
not quite 100% reflective). Stick a photodiode to the back of this
mirror, and connect it to an audio amplifier and speaker.
Fire the laser at a mirror on the  wall, and line it up so the beam
returns right back to the laser (i.e. beam at exactly 90 degrees to
the mirror on the wall)

You can now 'hear' any tiny movement of the wall via the speaker, e.g.
leaning on it, as it moves by a few hundred light wavelegths per
second.
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2001\02\04@152719 by Peter L. Peres

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Isn't the modulated beam, phase measurement method a variation of Fizeau's
experiment ? (the one with the spinning slotted discs with slots 180
degrees out of phase - 18th century ?).

Peter

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2001\02\04@155708 by Bob Blick

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>Isn't the modulated beam, phase measurement method a variation of Fizeau's
>experiment ? (the one with the spinning slotted discs with slots 180
>degrees out of phase - 18th century ?).

We all stand on the shoulders of giants..

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