Optomechanics
Shift of the cavity resonance. The transmission amplitude of a slightly detuned control beam (red line) through the cavity oscillates in time at the frequency of the mechanical motion.
Fabry-Perot cavity with a moving mirror. The red curve indicates one of the resonant optical modes.
Optomechanics is the discipline that studies the interaction of mechanical vibrations and electromagnetic fields in the visible/near-infrared spectral range. Since the experimental discovery of radiation pressure [Lebedev, 1900] physicists worldwide has been fascinated by the possibility to move macroscopic objects only through the momentum exchange with photons.
In 1970, Ashkin showed how focused light beams were able to trap dielectric particles, introducing for the first time the concept of optical tweezers as a precision tool to control/move particles and neutral atoms. With the introduction of gravitational waves interferometric detectors we get closer to the modern optomechanics. Giant mirrors, vibrating due to the gravitational wave effect, directly change the interferometric path of the control beams. With modern fabrication techniques we can keep the same concept and scale it down to the micrometric/nanometric scale: cavity optomechanics is finally born.
To understand the basic concepts, let's consider simple cavity composed by two mirrors (Fabry-Perot cavity), as the one sketched in the figure. For particular values of the radiation wavelength, light inside the cavity can form resonant modes, which constructively interfere with themselves after a round trip. Now, if one of the mirror is moving, the resonant mode condition changes, shifting the energy of the modes toward the blue (shorter cavity) or the red (longer cavity) sides of the spectrum.
In the reciprocal space of the frequencies this means to shift the lorentzian peak associated to the mode. If we use a control beam, as the red line in figure, and consider transmission through the cavity it is easy to see that the amplitude of the transmitted light changes at the frequency of the mechanical vibration.
By simply analysing the control beam we can get information on the cavity vibrational state!
But this is not the end the story. Actually, strong enough light beam can modify the vibrational state of the mechanical object. Fascinating phenomena such as optical spring effect, sideband cooling and lasing have been demonstrated. More details about the optomechanics can be found in this nice review:
M. Aspelmeyer, T. J. Kippenberg, F. Marquardt, Cavity Optomechanics, arXiv:1303.0733v1