  An optical cavity consisting of optically trapped mirrors makes a resonant
bar that can be stiffer than diamond. A limitation of the stiffness arises in
the length of the optical bar as a consequence of the finite light speed. High
laser power and light mass mirrors are essential for realization of a long and
stiff optical bar that can be useful for example in the gravitational-wave
detector aiming at the observation of a signal from neutron-star collisions,
supernovae, etc. In this letter, we introduce a parametric signal amplification
scheme that realizes the long and stiff optical bar without the need to
increase the laser power.
