We demonstrate the first absorption imaging of a single atom. Absorption depths of up to 2.6(2)% were observed for laser cooled174Yb+ions illuminated at 369.5 nm and imaged with a phase Fresnel lens.
Absorption of light is a fundamental process in imaging. The optical properties of atoms are thoroughly understood, so a single atom is an ideal system for testing the quantum limits of absorption imaging. Here we report the first absorption imaging of a single isolated atom, the smallest and simplest system reported to date. Contrasts of up to 3.1(3)% were observed in images of a laser cooled 174Yb+ ion confined in vacuum by a radio-frequency Paul trap. This work establishes a new sensitivity bound for absorption imaging with a 7800x improvement over the contrast previously observed in imaging a single molecule.
A microfabricated phase Fresnel lens was used to image ytterbium ions trapped in a radio frequency Paul trap. The ions were laser cooled close to the Doppler limit on the 369.5 nm transition, reducing the ion motion so that each ion formed a near point source. By detecting the ion fluorescence on the same transition, near-diffraction-limited imaging with spot sizes of below 440 nm (FWHM) was achieved. To our knowledge, this is the first demonstration of wavelength-scale imaging of trapped ions and the highest imaging resolution ever achieved with atoms in free space.