Observation and characterization of an optical spring

Recent theoretical developments have highlighted the potential importance of optical springs in interferometers for gravitational wave detection as a means for beating the standard quantum limit. We have observed an optical spring effect experimentally in a detuned Fabry-Perot resonator in which one mirror is mounted on a flexure so that it has a significant response to radiation pressure. The main effect of the optical spring, an observed shift in the mechanical resonance frequency of the moveable mirror, agrees well with a simple model.