waves distort space-time and produce forces in such a way that the distance
between free masses will alternately decrease and increase during the passage
of a gravitational wave. An important characteristic is that when there is elongation
in one direction there is compression in the perpendicular one. As a result,
a circle made of free masses will get successively elongated and contracted
in two perpendicular directions.
The amplitude of gravitational waves, the dimensionless parameter h,
is measured by the relative variation of distance between two free masses. The
absolute variation is therefore proportional to the distance between the two
masses. It would typically be as large as the size of an atom if
one could monitor the distance from the earth to the sun, and it would be about
one hundred millions times smaller for two points separated by a distance of
a few kilometers.
Such a small variation of distance can however be detected through the phenomenon
A laser Michelson interferometer is very sensitive to differential length variations
between its two arms and is ideally suited to the detection of gravitational
waves. Because of the extremely high sensitivity required, the length of the
arms must be hundreds of kilometers. Since this cannot be practically achieved
on earth, one uses multiple reflections between two mirrors to artificially
increase the measuring length. Fabry-Perot resonant cavities made of two mirrors
are currently employed in gravitational waves interferometers.
for the detection
of gravitational waves