We measured the Stark coefficient for the H-3(4)(1) --> 1D2(1) transit
ion of Pr3+:YAlO3, using the technique of Stark-modulated photon echoe
s. This gave a value of 58 kHz/(V cm-1) for the vector difference betw
een ground- and excited-state electric dipole moments. The resolution
with which Stark shifts could be measured in these experiments was app
roximately 500 Hz, which is more than an order of magnitude less than
the homogeneous linewidth.