Phase modulation of ultrafast laser pulses has been demonstrated recently by taking advantage of the time-dependent refractive index that takes place during rotational wave packet revivals in a gaseous sample [Phys. Rev. Lett. 88 (2002) 013903]. Here we explore the effect of laser intensity, physical properties of molecules, and temperature on rotational wavepacket revivals by femtosecond transient grating spectroscopy. Theoretical analysis of experimental data is used to predict the optimum conditions for the phase modulation and compression of ultrafast laser pulses. (C) 2003 Elsevier Science B.V. All rights reserved.