Gerakis, A; (2014) Controlling and probing molecular motion with optical lattices. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes the further improvement of an already developed by our group laser system capable of delivering high energy, frequency agile, flat-top pulses and its uses in non-resonant molecular scattering diagnostics in the form of coherent Rayleigh-Brillouin scattering, as well as for optical Stark deceleration of neutral H2 molecules. This laser system is capable of delivering two computer controlled flat-top pulses of variable duration (20~1000 ns) with energies up to 700 mJ per pulse and with linearly chirped frequencies up to 1.5 GHz. With the use of constant velocity lattices driven by this system we were able to accurately obtain coherent Brillouin scattering spectra of purified air in the hydrodynamic regime where, for the first time, we observed additional spectral peaks to the main Brillouin peak, as well as up to 40% reduction of the peak due to the interaction of the laser driven electrostrictive grating with the acoustic which was launched in the gas due to its thermalisation by the optical field. Furthermore, by utilising chirped frequency optical lattices, we were able to obtain accurate coherent Rayleigh-Brillouin spectra with signal-to-noise ratios in excess of 100, in a single laser shot ( 140ns) thus reducing the acquisition times needed for such spectra by ten orders of magnitude, rendering the technique ideal for combustion and transient flow diagnostics. Finally, we report on the use of this laser system as a tool for optical Stark deceleration of neutral H2 molecules, where through a Raman tagging scheme of the interacting molecules we are proposing an efficient way to monitor the interactions occurring within the decelerating optical lattice. We hope that this technique will pave the way for the production of narrow velocity spread molecular ensembles to be used in cold collisional studies as well as sympathetic cooling.

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