Spectral Hole Burning for Ultra-stable Lasers

We report on the measurement of uniaxial stress sensitivities of the spectral holes in rare earth doped crystal. This provides the necessary information for ab initio calculation of the acceleration sensitivity for a given crystal geometry, and provides the necessary base for optimizing the mounting of the crystal so as to decrease the vibration induced frequency instability. Furthermore, we report on a novel double heterodyne detection scheme which we have shown can be used to decrease the detection noise when locking a laser to the central frequency of a spectral hole, and thereby allows us to obtain a laser with fractional frequency instability of 1.7 x 10(-15) @ 1 s.