Positronium in superintense high-frequency laser fields

Abstract

The distortion induced by a superintense high-frequency laser field inhibits both ionisation of a ground state positronium atom (Ps) to emit e− and e+ and annihilation to decay into γ-rays. We apply high-frequency Floquet theory (HFFT) to evaluate the half-life for both ionisation and annihilation of Ps in either a linearly or circularly polarised field, over quiver amplitudes (governed by the ratio of laser field strength to the square of the oscillation frequency) extending to ∼100 au and beyond. We also consider the HFFT validity criteria, which set upper and lower bounds on the laser frequency, and present a generally applicable plot that facilitates determining the optimal quiver amplitude and laser intensity. For currently available lasers that satisfy the validity criteria, the laser-induced lifetimes become far longer than field-free values, but the ionisation lifetime is 105-fold or more shorter than the annihilation lifetime for para-Ps (spins antiparallel) and 108-fold shorter than that for ortho-Ps (spins parallel).