  Multiphoton processes of absorption photoluminescence have enabled a wide
range of applications including three-dimensional microfabrication, data
storage, and biological imaging. While the applications of two-photon and
three-photon absorption and luminescence have matured considerably,
higher-order photoluminescence processes remain more challenging to study due
to their lower efficiency, particularly in subwavelength systems. Here we
report the observation of it five-photon luminescence from a single
subwavelength nanoantenna at room temperature enabled by the Mie resonances. We
excite an AlGaAs resonator at around 3.6 um and observe photoluminescence at
around 740 nm. We show that the interplay of the Mie multipolar modes at the
subwavelength scale can enhance the efficiency of the five-photon luminescence
by at least four orders of magnitude, being limited only by sensitivity of our
detector. Our work paves the way towards applications of higher-order
multiphoton processes at the subwavelength scales enabled by the physics of Mie
resonances.
