I will discuss a recently discovered nonlinear-optical process called high-order sideband generation (HSG). High-order sideband generation occurs when a near-band-gap laser is transmitted through a semiconductor that is driven by strong Terahertz-frequency electric fields. The electron-hole pairs that are created by the near-band-gap laser are ripped apart by the Terahertz field, accelerated first away from and then back towards each other, and finally recollide. If they recombine after recollision, their excess kinetic energy is carried away by a sideband separated from the near-ir laser line by an even integer times the Terahertz frequency. Sidebands separated from the near-ir laser line by more than 100 times the Terahertz frequency have been observed, making HSG the highest-order nonlinear optical process ever observed in a solid, to our knowledge. Careful analysis of the polarization states of high-order sidebands shows they carry the imprint of the Berry curvature of the semiconductor bands in which electron-hole pairs were accelerated by the strong Terahertz field.

This is joint work with B. Zaks, H. B. Banks, Q. L. Wu, D. C. Valovcin, S. Mack, A. C. Gossard, L. Pfeiffer, and R. B. Liu. This work was supported by the NSF under grants DMR 1405964 and 1710369.

References:
B. Zaks, R.-B. Liu and M. S. Sherwin, Experimental observation of electron-hole recollisions, Nature 483, 7391 (2012)

H. B. Banks, Q. L. Wu, D. C. Valovcin, S. Mack, A. C. Gossard, L. Pfeiffer, R. B. Liu and M. S. Sherwin, Dynamical birefringence: electron-hole recollisions as probes of Berry curvature, Phys. Rev. X 7, 041042 (2017).