Controlled orientational photoselection via three-pulse excitation

A new technique for the precise control of the orientation of a photoselected excited-state array of molecules based on the simultaneous interaction of three orthogonally polarised picosecond pulses in a thin sample is demonstrated. This allows the preparation of a continuous range of both positive and negative excited-state alignments whilst retaining cylindrical symmetry about the laboratory Z axis. The photoselection process is fully characterised in terms of pulse intensity, propagation angle and material refractive index. Experimental results are presented for the photoselection and orientational relaxation of rhodamine 6G and resorufin in isotropic solutions of ethylene glycol.