Towards optomechanical systems and high precision measurements with rare-earth doped crystals

This work has been done in order to use spectral holes burnt in the absorption spectrum or rare-earth doped crystals to create an optomechanical coupling with a micro-resonator. By doing so, the objective is to study quantum properties of a macroscopic mechanical object. Such a study could be of great interest in the field of quantum information, fundamental physics or high sensitivity sensing. The ⁷F₀-⁵D₀ transition of europium ions used as a dopant in an yttrium orthosilicate crystal show an inhomogeneous broadening of the resonance that can reach 2 GHz for 0.1 % doping due to imperfection of the crystalline matrix. By maintaining the crystal below 5 K, one can use a narrow linewidth laser to create a persistent narrow transmission window, dependent on the homogeneous linewidth of the transmission, at any chosen frequency within the absorption spectrum. Such structures, called spectral holes, are made possible by optically pumping a given class of ions into dark states whose lifetime at 4 K can reach tens of hours. The development of a new method to follow the frequency of spectral holes, based on double heterodyne detection of a dispersive signal is presented, as well as a measurement of the spectral hole frequency sensitivity to uniaxial constraints applied to the crystal. This measurement is useful to properly design the resonator and can provide an upper limit to the detection noise in order to see an effect of the coupling with this resonator. A first study of the optical setup necessary to burn spectral holes at the base of a 10×10×100 µm cantilever resonator is given. Finally, the influence of the new detection scheme on the frequency stability measurement of spectral holes is discussed.

rare-earth doped crystals, nanotechnologie, optomechanics, light-matter interaction