Aligned Molecules for X-Ray Microprobe Studies

We prepare a sample of aligned molecules for experiments with 100-ps x-ray pulses at the Advanced Photon Source. Established techniques of adiabatic alignment by 10-ns pulses are not best suited for this application because of the low laser repetition rates (10-100 Hz). Instead, we choose to align adiabatically with amplified chirped pulses from a Ti:sapphire laser system (800 nm, 1.3 mJ, 120 ps, 1 kHz). In these laser-only experiments, we investigate the alignment of cold $\rm{N_{2}}$ and $\rm{CF_{3}Br}$ molecules by detection of the charged fragments following ionization by a short (50fs) 800nm laser pulse. Molecules from a supersonic jet intersect an aligning pulse of variable linear polarization and variable delay relative to a near-colinear circularly-polarized dissociating probe pulse. The resulting ions are accelerated in a velocity-map imaging spectrometer toward a position-sensitive microchannel plate detector; the polarization dependence of this fragment distribution indicates alignment of the sample.