LSU Theoretical Physicists Further Our Understanding on High-Frequency Light Generation in Crystals

An imperfect recollision in which the electron and hole centers do not exactly overlap, leading to an electron-hole-pair polarization energy upon recollision. In the ERM, we also keep track of the phase accumulated along the trajectories. (b) Band gap energy (in units of ω0=0.0285) of monolayer hBN with annotated points of interest. The gray discs around M1 and M2each has radius 0.1.

Physics journal PRL features LSU ultrafast AMO physics theoretical research.

Physical Review Letters, PRL, has published a paper by LSU Physics Professor Mette Gaarde and Postdoctoral Researcher Lun Yue, discussing the wide-ranging manifestations and experimental consequences of imperfect recollisions between electron and hole wave packets in light-driven crystals.

In the last few decades, the generation of high-frequency light in gases, by the so-called high-harmonic generation (HHG) process, has led to the production of the shortest light-pulses available, with durations on the attosecond (=10-18s) timescale. This has opened up the new discipline of “attosecond physics” and the possibility of tracking the motion of electrons on their own natural time scales. More recently, HHG in crystals has attracted a lot of attention, both as a means of engineering compact attosecond light sources, and as a promising tool to probe structural, energetic, and topological features of condensed phase materials.

The paper by Yue and Gaarde, Imperfect recollisions in high-harmonic generation in solids (Phys. Rev. Lett. 124, 15320), theoretically investigates HHG in hexagonal boron nitride illuminated by intense infrared laser pulses. “We show that even imperfect recollisions between spatially extended electron and hole wave packets can produce high-frequency laser light in crystalline solids,” said Gaarde.

The production of light in HHG can generally be understood as a three-step process in which the intense laser field first leads to tunneling of an electron from the valence to the conduction band, then accelerates the electron and hole wave packets, so that when they recollide with each other in space their excess energy is emitted as high-frequency light.

“Our work extends this three-step model and shows for the first time that the recollision step can be imperfect, so that the recolliding electron and hole wave packets only partially overlap,” explained Gaarde. “Our model results are in good agreement with our fully quantum mechanical results, and our paper discusses the wide-ranging manifestations and potential experimental consequences of imperfect recollisions in light-driven crystals.”

Yue notes that “There are so many open questions in this emerging and exciting field of nonlinear light-crystal interactions. We are very happy to have developed a theoretical model that can capture the underlying physical mechanism of imperfect recollisions, as well as explain quantitative features such as timings of the short bursts of light”.

Gaarde is the Les and Dot Broussard Alumni Professor of Physics and has been at LSU since 2003. She works on ultrafast and strong-field processes in atoms, molecules, and solids. Her team at LSU has strong ties to several experimental programs in the US and in Europe. Working with faculty members in this group are postdoctoral associates and a number of graduate students. Yue has been a postdoc in the group for two years and his research is focused on light-driven ultrafast dynamics in crystals.

Physical Review Letters (PRL), the world’s premier physics letter journal and the American Physical Society’s flagship publication. Since 1958 it has contributed to APS’s mission to advance and diffuse the knowledge of physics by publishing seminal research by Nobel Prize–winning and other distinguished researchers in all fields of physics.

Imperfect Recollisions in High-Harmonic Generation in Solids
Lun Yue and Mette B. Gaarde
Phys. Rev. Lett. 124, 153204 – Published 16 April 2020


Mimi LaValle
LSU Department of Physics & Astronomy