Dresden 2009 – wissenschaftliches Programm
HL 15.6: Vortrag
Dienstag, 24. März 2009, 10:45–11:00, POT 51
The non-linear optical properties of single and multilayer graphene — •Rainer Stöhr1, Roman Kolesov1, Fedor Jelezko1, Jens Pflaum2, and Jörg Wrachtrup1 — 13rd Physics Institute, Stuttgart University, D-70659 Stuttgart — 2Julius-Maximilians-University of Würzburg, Institute of Physics, Experimental Physics VI, D-97074 Würzburg and Bavarian Centre for Applied Energy Research e.V. (ZAE Bayern), D-97074 Würzburg
By optically exciting graphene flakes with pico- and femtosecond pulses of different wavelengths and with pulse power densities in the order of GW/cm2 we can not only observe the well known G-line and D’-line but also the anti-Stokes G line. In addition, a broad background can be detected which peaks at the excitation wavelength and which extends by about 3000 wavenumbers into the red and about 2500 wavenumbers into the blue. Both, the anti-Stokes G line and the background were found to be of cubic dependence with respect to incident laser power.
We can explain the occurrence of the anti-Stokes G line as a result of a stimulated Raman process due to the pulsed laser excitation.
It will be evidenced that simple heating effects of the flakes cannot account for the broad continuum radiation; however this feature can be assigned to an electron-hole scattering mechanism which depends primarily on the number of excited charge carrier pairs.
As a possible application we show that the continuum radiation can be used to significantly improve the contrast of a confocal image compared to that mapped at the Raman lines and thereby will pave the way of a detection mechanism of high sensitivity.