Ultrashort Pulses for Far-Field Nanoscopy

TL;DR

This paper demonstrates that ultrashort pulses can be focused to nanometer-scale spots and used to excite quantum systems with nanoscale precision, enabling a new approach to far-field nanoscopy.

Contribution

It reveals that ultrashort pulses can be focused to nanometer scales and excite two-level systems via intensity-dependent interactions, leveraging quantum electrodynamics effects.

Findings

Ultrashort pulses can be focused to nanometer-scale spots.

Excitation probability depends on field intensity, not amplitude.

Proposes a new far-field nanoscopy technique using attosecond pulses.

Abstract

We show that ultrashort pulses can be focused, in a particular instant, to a spot size given by the wavelength associated with its spectral width. For attosecond pulses this spot size is within the nanometer scale. Then we show that a two-level system can be left excited after interacting with an ultrashort pulse whose spectral width is larger than the transition frequency, and that the excitation probability depends not on the field amplitude but on the field intensity. The latter makes the excitation profile have the same spot size as the ultrashort pulse. This unusual phenomenon is caused by quantum electrodynamics in the ultrafast light-matter interaction regime since the usually neglected counterrotating terms describing the interaction with the free electromagnetic modes are crucial for making the excitation probability nonzero and depend on the field 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.