Special Seminar

An ultrafast journey through nanometres, attoseconds, and Teslas

Shawn Sederberg, SFU Engineering Science
Location: P8445.2

Friday, 03 June 2022 02:30PM PDT


When light impinges on a material, a signature of the material’s electric polarization response is imprinted onto the outgoing optical fields. Sampling the electric field oscillations comprising femtosecond (1 fs = 10^{-15} s) laser pulses in the time domain unlocks these prior interactions. Doing so requires a sub-cycle trigger event, but provides real-time insight into electron dynamics and decoherence mechanisms on similarly brief timescales. In the first part of this seminar, I will present a solid-state platform for attosecond (1 as = 10^{-18} s) metrology that functions in ambient conditions. By applying single-cycle optical pulses to large bandgap solids, namely quartz, tunnelling-like electronic transitions become temporally confined to sub-femtosecond bursts. The change in electrical and optical properties of the material accompanying the arrival of the electron wavepacket in the conduction band is harnessed as a trigger for sampling optical fields. This technique, referred to as “nonlinear photoconductive sampling (NPS),” is used to sample femtosecond laser pulses spanning the ultraviolet to the mid-infrared, more than 1 petahertz (1 PHz = 10^{15} Hz) of continuous bandwidth. The signal-to-noise ratio and dynamic range of the technique surpass that of conventional attosecond techniques by 3-4 orders of magnitude.

While NPS has a direct connection to attosecond metrology, it is also more broadly connected to the topic of “coherent control.” In coherent control, laser pulses are used to impart coherence to electrons that persists for a brief time after the optical fields subside. In the second part of this seminar, I will introduce the topic of structured light and demonstrate that coherent control using structured optical modes can be used to transduce electric field structure from the optical beams to current structure in materials. We place a particular emphasis on exciting ring currents for the purpose of controlling magnetic fields on femtosecond timescales. More broadly, coherent control using structured light could enable control of collective electron excitations and spin structures in quantum systems.

Finally, I’ll provide a brief overview of my start at SFU and my future plans.