Sub-wavelength terahertz imaging through optical rectification.

We record a sub-wavelength terahertz image of a caster sugar grain thanks to optical rectification in the sample excited with a femtosecond laser beam. The lateral spatial resolution of this technique is given by the laser spot size at the sample and here its measured value is 50 μm, i.e. ~λ/12. We give an estimation of the ultimate resolution that could be achieved with this method.