Theory of sub-Doppler Autler-Townes splitting in molecules: Alignment and orientation of the angular momentum in nonpolar molecules

Within a density matrix framework, an analytical expression for the optical -optical double resonance (OODR) line shape for a molecule in the presence of a strong coupling laser is derived. The coupling laser is tuned to a tra nsition between the upper level in the OODR sequence and another excited le vel which is not part of the OODR sequence. The pump and probe lasers are t reated perturbatively, while the coupling laser is treated exactly. The lin e shape reveals sub-Doppler Autler-Townes (AT) splitting of the states \J,m ] within the highest excited level. The splitting depends on \m\(m) for lin early (circularly) polarized coupling fields. m-state selectivity and there fore alignment and orientation of the angular momentum can be achieved by t uning the probe laser in the presence of a coupling field which is sufficie ntly strong to resolve the m-dependent AT splittings. m selectivity is anal yzed for e and f parity (1)Pi (g) levels in diatomic molecules. A method to orient nonpolar diatomics using circularly polarized lasers is proposed. ( C) 2001 American Institute of Physics.