Subwavelength THz imaging of graphene photoconductivity
  Using a spatially structured, optical pump pulse with a THz probe pulse, we are able to determine spatial variations of the ultrafast THz photoconductivity with sub-wavelength resolution (75 $\mu m \approx \lambda/5$ at 0.8 THz) in a planar graphene sample. We compare our results to Raman spectroscopy and correlate the existence of the spatial inhomogeneities between the two measurements. We find a strong correlation with inhomogeneity in electron density. This demonstrates the importance of eliminating inhomogeneities in doping density during CVD growth and fabrication for photoconductive devices. 
Samuel M. Hornett, Rayko I. Stantchev, Martha Z. Vardaki, Chris   Beckerleg, Euan Hendry
physics.optics cond-mat.mes-hall