Europhys. Lett.
Volume 47, Number 5, September 1999
Page(s) 545 - 551
Section General
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00422-6

Europhys. Lett, 47 (5), pp. 545-551 (1999)

High-sensitivity optical measurement of mechanical Brownian motion

Y. Hadjar, P. F. Cohadon, C. G. Aminoff, M. Pinard and A. Heidmann

Laboratoire Kastler Brossel, case 74
4 place Jussieu, F-75252 Paris Cedex 05, France

(received 16 April 1999; accepted in final form 1 July 1999)

PACS. 05.40Jc - Brownian motion.
PACS. 04.80Nn - Gravitational wave detectors and experiments.
PACS. 42.50Lc - Quantum fluctuations, quantum noise, and quantum jumps.


We describe an experiment in which a laser beam is sent into a high-finesse optical cavity with a mirror coated on a mechanical resonator. We show that the reflected light is very sensitive to small mirror displacements. We have observed the Brownian motion of the resonator with a very high sensitivity corresponding to a minimum observable displacement of $2\times
10^{-19}\;{\rm m}/\sqrt{{\rm Hz}}$.


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