The dynamics of rotational wave packets of laser-aligned linear molecules was studied with femtosecond laser pulses in a pump-probe configuration. The alignment produced with a pump beam creates a transiently anisotropic medium, which exhibits birefringence and also a dependence of ionization on the mutual orientation of the polarizations of the probe and pump beams. The induced molecular alignment was observed via variations of the yields of photoelectrons in strong field ionization. In addition, the induced transient birefringence due to alignment revivals altered the nonlinear interaction of the probe beam with the gas, resulting in delay dependent modulation of the probe beam. The revival signatures measured for N-2, CO and C2H2 gas molecules were in good agreement with the calculated molecular alignments taking into account the effects of electronic structure and molecular symmetry.