Positrons are short-lived subatomic particle with the same mass as electrons and a positive charge.
They are used in medicine, e.g.
in positron emission tomography (PET), a diagnostic imaging method for metabolic disorders.
Positrons also exist as negatively charged ions, called positronium ions (Ps-), which are essentially a three-particle system consisting of two electrons bound to a positron.
Now, commercially available lasers are capable of producing photons that carry enough energy to bring the electrons of negatively charge ions, like Ps?, to doubly-excited states, referred to as D-wave resonance.
Positronium ions are, however, very difficult to observe because they are unstable and often disappear before physicists get a chance to analyse them.