Detecting and characterizing frequency fluctuations of vibrational modes
  We show how frequency fluctuations of a vibrational mode can be separated from other sources of phase noise. The method is based on the analysis of the time dependence of the complex amplitude of forced vibrations. The moments of the complex amplitude sensitively depend on the frequency noise statistics and its power spectrum. The analysis applies to classical and to quantum vibrations. 
Z. A. Maizelis, M. L. Roukes, and M. I. Dykman
cond-mat.mes-hall cond-mat.stat-mech