Controlling molecular alignment

The molecules in a normal gas point in random directions. With a short laser pulse, a rotational wavepacket can be created, leading to field-free alignment of the molecules after the laser pulse has passed. Due to quantization, the rotational wavepacket can revive, repeatedly aligning at regular intervals. This thesis reports work on controlling, measuring, and using molecular alignment in experiments.; The alignment of a molecule can be measured by Coulomb explosion imaging. A strong laser pulse can multiply ionize a molecule, leading to rapid dissociation. By measuring the velocities of the fragments, the alignment of the original molecule can be determined. Experiments using Coulomb explosion imaging to image time-dependent molecular alignment and structure are described.; By applying multiple laser pulses, the evolution of rotational wavepackets can be controlled. An extra laser pulse can achieve field-free three-dimensional alignment in asymmetric top molecules. Rotational wavepackets can be enhanced or annihilated by extra laser pulses by making use of the rotational revival structure. Weak laser pulses at times of fractional revival can cause dramatic changes to the wavepacket evolution by changing the relative phases within the wavepacket.; We performed a laser-induced electron diffraction experiment on nitrogen molecules, using alignment to effectively crystallize the gas. Early results suggest that molecular structure can be measured using this technique. We developed a new technique for measuring the angular dependence of strong-field ionization in molecules. Applying this technique to nitrogen, we found that it is more likely to ionize when the molecular axis is aligned with, rather than against the electric field of a linearly polarized ionizing pulse. These and future experiments using molecular alignment are discussed.