This is a laboratory apparatus for mapping and imaging of radio frequency (RF) electric fields at resolutions below the usual RF wavelength limit. Rubidium atoms are placed in the glass cylinder (on the right), which is illuminated at opposite ends by red and blue laser beams. The cylinder (2.5 by 7.5 centimeters in size) moves left on a track to enable the narrow laser beams to scan its entire width. The antenna (on the left) generates an RF field, which, depending on its frequency, has a certain effect on the spectrum of light absorbed by the atoms. By measuring this effect researchers can calculate and map the RF field strength as a function of position in the cylinder.