Measuring intracavity phase changes by use of double pulses in a linear cavity

We report the use of a mode-locked linear-cavity Ti:sapphire laser as a sensitive phasemeter. We were able to generate two pulses in the cavity by placing an absorbing-dye jet in the middle of the cavity. A voltage applied to an intracavity LiNbO(3) crystal modified the phase velocity for one of the two pulses at each of its passes. We could then measure accurately the change in optical cavity length by observing a beat frequency between the two pulses. We measured the ratio of the r(33) to r(13) electro-optic coefficients in LiNbO(3) to be 3.57+/-0.1 , in close agreement with the accepted value of 3.62.