  We propose a novel approach for efficient tuning of optical properties of a
high refractive index subwavelength nanoparticle with a magnetic Mie-type
resonance by means of femtosecond laser irradiation. This concept is based on
ultrafast photo-injection of dense (>10^20 cm^-3) electron-hole plasma within
such nanoparticle, drastically changing its transient dielectric permittivity.
This allows to manipulate by both electric and magnetic nanoparticle responses,
resulting in dramatic changes of its scattering diagram and scattering cross
section. We experimentally demonstrate 20 % tuning of reflectance of a single
silicon nanoparticle by femtosecond laser pulses with wavelength in the
vicinity of the magnetic dipole resonance. Such single-particle nanodevice
enables to design fast and ultracompact optical switchers and modulators.
