Subfemtosecond pulse generation by rotational molecular modulation

We extend a recent suggestion for the generation of subfemtosecond pulses b y molecular modulation [Phys. Rev. Lett. 81, 2894 (1998)] to the rotational spectrum of molecular hydrogen (H-2). When a rotational transition \a] --> \b] is strongly driven (\rho(ab)\ = 0.5) the generation and phase-slip len gths are of the same order and the Raman spectrum has approximately Bessel function sideband amplitudes. Numerical simulation predicts that this spect rum (generated in a 14-cm-long cell at l-atm pressure of H-2) will compress into a train of pulses with 94-fs pulse separation and a pulse length of 0 .5 fs. (C) 1999 Optical Society of America.