Fabry-Perot effects in the exponential decay and phase shift reflectivity measurement methods

The exponential decay and phase shift reflectivity measurement methods are examined for a real optical cavity, i.e., one that includes mechanical vibrations and light source fluctuations in wavelength and amplitude. We compare the two methods and examine the problems inherent in each and present methods for overcoming these. Both methods are shown to be excellent for measuring high reflectivity cavity losses (particularly for the free electron laser case) although suitable precautions should be taken.