Controlling molecules with lasers and lasers with molecules

Abstract

I investigate quantum control of spin in molecules using shaped ultrafast lasers and the dynamics of those lasers when their cavities are modified to include programmable molecular masks. The ability to control quantum phenomena has had several large successes over the last decade. This field, known as Quantum Control, uses closed loop learning algorithms to shape ultrashort laser pulses in order to produce a desired state or state change. Interesting pulse shapes have been able to break chemical bonds, drive chemical reactions, selectively excite molecular states, and most recently, control photoisomerization in proteins [1, 2, 3]. In this thesis I began by seeking to apply this technique to manipulate spin. In our early work we pursued polarizing electron spins and nuclear spins for NMR Quantum Computation. We studied the electron spin triplet state properties of several molecules. Through this work we recognized that the laser and pulse shaper we were using could be modified to utilize the triplet properties of our molecules. We created a molecular triplet state spatial light modulator (SLM) to be used both outside and inside the laser cavity for ultrafast pulse shaping. The SLM consists of a liquid or thin film sample with a strong triplet state absorption.

(cont.) The molecule is selected to be transparent to the target light before pumping and strongly absorptive when pumped into the triplet state. The sample is exposed to laser light reflected off of a DMD chip to produce a 2D pattern to spatially populate the triplet ground state. This is, to our knowledge, the first triplet state ultrafast pulse shaper and the first all-optical inter-cavity spatial frequency modulator.