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Thermal Fluctuations

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posted on Thu, Jan 7 2010 6:19 PM

we're having a weird phenomenon. We calculate the spring constant of the tip
using the thermal fluctuation method. It generally works well but lately we
have a strange result. Tips with K > 4 n/m we used before appear to have
thermal fluctuation signal which is much reduced. The peak of the FFT signal drops almost an order
of magnitude with the calculated spring constant going up 2-5 times
what it used to be. This happen even at 10Mhz sampling rate, on more than
one machine and with tips of 2 different manufacturers!
The strength of the laser signal from the tips themselves remain the same.
When we measure with the "stiffer" tips they appear to be the same as before.
Do you know of any process that can cause the thermal fluctuation signal to
appear/or actually to be reduced?

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