  The electromagnetic response of a nanoparticle of an ion-doped polymeric
elastic insulator, commonly called as an electret, is considered in the
continuum model of a uniformly charged elastic sphere. The spectral formulae
for the frequency of optically induced spheroidal and torsional shear
oscillations driven by bulk force of elastic and dielectric stresses are
obtained in analytic form. Particular attention is given to relaxation
dielectric mode of the electrostriction response and its stability in the
lowest quadrupole mode. The practical usefulness of ultrafine particles of
electrets as a biolabels capable of accumulating likely-charged inclusions
uniformly dispersed over the spherical volume of an elastic matrix is briefly
discussed.
