Investigations of electron wave-packet dynamics and high-order harmonic generation in laser-aligned molecules

We review recent work examining electron dynamics and high-order harmonic generation (HHG) in molecules exposed to high intensity (10(13)-10(15) W cm(-2)) ultrashort pulse laser fields. The use of adiabatic laser alignment techniques, using relatively long duration (300 ps) laser pulses of moderately high intensity (10(11)-10(12) W cm(-2)) enabled us to perform the first experiments investigating the role of the angle between the laser polarization vector and the molecular axis. We have shown that alignment of a sample can enhance the harmonic yield by a small but significant factor. HHG in model H-2 and H-2(+) molecules was treated theoretically by numerical integration of the Schrodinger equation. The unique influence of the dipole phase in molecular HHG is clearly demonstrated and is shown to offer a consistent explanation for our experimental observations. The electron wavepacket dynamics exhibit strong interference effects that result in the reduction or enhancement of harmonic yield at certain alignment angles. Experiments to further investigate these effects and to increase the modulation of the harmonics by molecular alignment are discussed.