Indexed on: 09 Nov '16Published on: 07 Nov '16Published in: Nature Photonics
Terahertz (THz) near-field imaging is a flourishing discipline1, 2, with applications from fundamental studies of beam propagation3 to the characterization of metamaterials4, 5 and waveguides6, 7. Beating the diffraction limit typically involves rastering structures or detectors with length scale shorter than the radiation wavelength; in the THz domain this has been achieved using a number of techniques including scattering tips8, 9 and apertures10. Alternatively, mapping THz fields onto an optical wavelength and imaging the visible light removes the requirement for scanning a local probe, speeding up image collection times11, 12. Here, we report THz-to-optical conversion using a gas of highly excited Rydberg atoms. By collecting THz-induced optical fluorescence we demonstrate a real-time image of a THz standing wave and use well-known atomic properties to calibrate the THz field strength.