PSN-L Email List Message

Subject: RE: Lehman seismometer movement
From: Jack Ivey ivey@..........
Date: Tue, 15 Mar 2011 22:38:50 -0400

Your analysis seems a bit pessimistic.  There's no need to settle=20
for a 50 cm arm - for a mirror on a separate suspension coupled to=20
the proof mass 1 cm would seem achievable, which, combined with a
10 m long arm gives a gain of 1000 without multiple mirror trips. =20
The information I have says that the surface waves for a magnitude=20
6 quake at 60 degrees have ground displacements of 10 microns. =20
This would give a beam displacement of 1 cm; hardly tiny.


>    Work it out? You can easily detect a movement of 100 nano metres.
>If you have a 50cm boom and mount a laser on it and your house is 10=20
>metres long, you would get a spot movement of just 2 microns. OK, you=20
>could use multiple reflections of a laser beam and get maybe 32 microns,
>but this is still a very tiny spot movement.

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