  Photoelastic coefficients of beta-BaB2O4 and Li2B4O7 crystals are calculated
on the basis of piezooptic measurements performed with interferometric
technique and the elastic compliance and stiffness data. Using the experimental
results, the acoustooptic (AO) figure of merit (FM) has been estimated for the
possible geometries of AO interaction. It is shown that the AO FM for the ABO
and LTB crystals reach respectively the values M2=243.4*10-15s3/kg and
M2=2.57*10-15s3/kg, if the interaction with the slowest ultrasonic waves
(v=933.5m/s and v=3173m/s) is concerned. The directions of propagation and
polarization of those acoustic waves are obtained on the basis of construction
of indicative surfaces of the acoustic wave velocities.
