Example of FEL


THz sideband generation

•Electorn-hole recollisionunder intense THz field results in high number of side bands generation
•Precise imprint of THz frequency on the NIR laser carrier



Focused NIR laser and THz radiation in the quantum well structure is used for side bands generation.

Experimental observation of multiple side bands.


Excitonsin the quantum well are resonantly induced with the aid of the near-IR laser. External THz field modulates excitonpotential landscape resulting in transfer of THz quanta to the excitonicstate. In the process of radiative decay the near-IR fundamental as well as multiple sidebands are emitted.


1. B. Zaks, R.B. Liu, and M.S. Sherwin “Experimental observation of electron-hole recollisions” Nature, 483, 580-583 (2012).

2. H. Banks, B. Zaks, F. Yang, S. Mack, A.C. Gossard, R. Liu, and M.S. Sherwin “Terahertz electron-hole recollisionsin GaAs/AlGaAsquantum wells: robustness to scattering by optical phonons and thermal fluctuations” Phys. Rev. Lett. 111, 267402 (2013).


THz harmonics generation

•Harmonic generation in THz extends available frequency range
•High FEL power results in effective conversion ratio





Third harmonic generation in highly reflective InAsand Si semiconductor wafers.
Saturation is observed for 3 kV/cm THz field.


Setup for THz harmonics generation.

     Intricate interplay between interbandand intrabanddynamics in graphene is expected to result in novel non-linear effects. High harmonic generation in THz region is one example of these phenomena. According to recent theoretical work [1] high harmonic generation is predicted in THz region with a high efficiency in undopedsingle layer graphene at low temperatures. This can result in extremely broad THz range extension.


1. I. Al Naib, J.E. Sipe, and M.M. Dignam(arXiv:1407.1273 [physics.optics], 2014).

2. D. Valovcin, M.S. Sherwin, work in progress.