Etude du couplage optomécanique dans une cavité de grande finesse; observation du mouvement Brownien d'un miroir

Abstract : The topic of this thesis is the theoretical analysis of the
optomechanical coupling effects in a high-finesse optical cavity, and the experimental realization of such a device.
Radiation pressure exerted by light has been of great theoretical interest since it limits the sensitivity of high precision optical measurements. In particular, the sensitivity of interferometric measurements of gravitational wave is limited by the so called standard quantum limit which is due to two fundamental sources of noise : the photon noise of the laser beam and the fluctuations of the mirrors position due to radiation pressure. We discuss here radiation pressure induced effects in high-finesse optical
cavity with a movable mirror. The internal field stored in such cavity can be orders of magnitude greater than the input field, and it's radiation pressure force can change the physical length of the cavity. In turn, any change in the mirror's position changes the phase of the out put field. This optomechanical coupling leads to an intensity-dependent phase shift for the
light equivalent to an optical Kerr effect. Such a device can then be used for squeezing generation or quantum nondemolition measurements.
In the experiment that we have realized, we send a laser beam in to a high-finesse single-port optical cavity with a movable mirror coated on a high Q-factor mechanical resonator. Quantum effects of radiation pressure become therefore, at low temperature, experimentally observable. However, we have shown that the phase of the reflected field is very sensitive to small mirror displacements, which indicate other possible applications of this
type of device like high precision displacements measurements. In
particular, we have been able to observe the Brownian motion of the moving mirror. We have also used an auxiliary intensity modulated laser beam to optically excite the acoustic modes of the mechanical resonator. This allows to characterize the mechanical response of the resonator and the coupling between light and acoustic modes. We have finally obtained a sensitivity of
2x10^(-19) m/sqrt(Hz), in agreement with theoretical prediction.
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Yassine Hadjar. Etude du couplage optomécanique dans une cavité de grande finesse; observation du mouvement Brownien d'un miroir. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1998. Français. ⟨tel-00004675⟩

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