Authors: Greg Smail
Source: Deep Blue (University of Michigan) (article, 2023-01-01)
Field: Chemistry — Electrochemistry

Investigation of Magneto-Electric Rectification at the Molecular Level The role of the optical magnetic field in light-matter interactions is often neglected due to its relative weakness with respect to the optical electric field. However, the magnetic field of light can interact strongly with matter in magneto-electric interactions where it acts jointly with the optical electric field to drive optical nonlinearities. The inclusion of the magnetic field dynamically breaks parity-time symmetry, so magneto-electric interactions can take place even in materials where static symmetry prohibits all-electric second order interactions. This thesis further advances the understanding of these magneto-electric nonlinearities, with a focus on magneto-electric rectification. Experimental and computational methods were used to characterize the magneto-electric rectification moment. The first experimental observation of magneto-electric rectification is reported. Time-resolved pump-probe experiments show a strong, ultrafast pump-induced second harmonic radiation signal in a sample with inversion symmetry. It is shown that magneto-electric rectification is the only process that is consistent with the experimental results. The design of a second experiment based on measuring magneto-electric rectification induced birefringence is presented that would offer improved sensitivity and permit a measurement of the magnitude of the rectification field. A classical model of magneto-electric interactions is used to simulate the magneto-electric response of a material to an optical pulse. The role of two enhancement mechanisms, parametric resonance and molecular torque, are analyzed in detail. These enhancement mechanisms allow the observation of nonlinear relativistic magnetic effects at non-relativistic intensities. A generalized time-dependent density matrix theory is presented that predicts the intensity, frequency, and polarization dependence of the rectification effect. This quantum theory is used to create a second computational model of magneto-electric rectification. Simulation results of the predicted rectification magnitude from both the classical and quantum models are presented and discussed. Both models predict an ultrafast timescale for the rectification moment and show the dependence of the duration and magnitude of the simulation output on molecular properties. The temporal characteristics predicted by the models are in excellent agreement with the experimentally observed rectification signal. The results presented in this thesis show the first experimental observation of magneto-electric rectification as well as the first computational analysis of the temporal characteristics of the rectification moment. Future research into magneto-electric nonlinearities could provide direct measurements of the magnitude of the rectification field. This measurement could be accomplished by using the induced birefringence experimental design. Applications of this work include ultrafast all-optical switching, new methods of terahertz generation, and energy conversion. Rectification ; Magneto ; Physics ; Electrical engineering ; Engineering ; Magnet ; Voltage Electrochemical Analysis and Applications