Ultrashort Pulses for Far-Field Nanoscopy

Abstract

We show that ultrashort pulses can be focused, at a particular instant of time, to a spot size given by the wavelength associated to its spectral width. For attosecond pulses this spot size is within the nanometer scale. Then, we show that a train of coherent ultrashort pulses can be used to excite a two-level system with an optical transition with a probability that depends on the light intensity, thereby with the same spot size. The excitation process is enabled due to quantum electrodynamics in the ultrafast light-matter interaction regime where the rotating-wave approximation is not valid. Indeed, the usually neglected rotating terms are decisive to make the excitation probability nonzero and depending on the light intensity. These results suggest that a train of coherent attosecond pulses could be used to excite fluorescent markers with nanoscale resolution. The detection of the light emitted after fluorescence, or any other method used to detect the excitation, could then lead to a new scheme for far-field light nanoscopy.