Abstract
We studied the nonlinear optical properties of single layer graphene using high terahertz (THz) fields. With the use of a back gate and cooling down the sample to cryogenic temperatures we are able to spectrally probe the nonlinear THz properties of intrinsic to highly doped graphene. The carrier density strongly affects the nonlinear properties of graphene; in the low doping and high THz field regime, an increase of the transmission on the order of 4% is found in our experiments. At higher doping levels we observe a larger relative nonlinear response: the larger the doping in the single layer the larger the relative field induced increase in transmission becomes. In all experiments, the THz field is opposing the effect of the gate, but field effects are never larger than the doping effects. We use the thermodynamical model for a hot electron gas also used by Mics et al (2015 Nat. Commun. 6 7655) to simulate our data and study the effects of doping on the nonlinear properties of single layer graphene. We find that the highest carrier temperatures are obtained in low doped graphene. The model shows a good qualitative agreement with our data for high doping levels. Nevertheless our results demonstrate the limitation of the model for low doping levels. Our results are a road map for further explorations for the control of nonlinear light–matter interaction and functionalization of graphene layers in active THz devices in which carrier temperature and saturable absorption play a role.
Highlights
The unique electronic and optical properties of graphene stem from its relativistic low energy band dispersion
An onset of conductivity is centered around the value of twice the chemical potential, which is the frequency regime where interband transitions start to contribute to the optical response, above which the conductivity is reaching σ0 [2]
The thermodynamical model used by Mics et al provides guidelines on how to increase the efficiency of graphene devices relying on the extraction of high-energy electrons; a higher electron temperature is beneficial, graphene should be low doped such that the THz beam only heats a small number of carriers, heating them to extremely high temperatures [8]
Summary
Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. G Gäumann1, I Crassee2,3 , N Numan4,5, M Tamagnone6,7, J R Mosig6, J-M Poumirol8, J-P Wolf2 and T Feurer1 Keywords: nonlinear THz spectroscopy, high terahertz (THz) fields, graphene layers Any further distribution of Supplementary material for this article is available online this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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