Recently, it was shown that a Mie particle in an evanescent field ought to experience optical forces that depend on the helicity of the totally internally reflected beam. As yet, a direct measurement of such helicity-dependent forces has been elusive, as the widely differing force magnitudes in the three spatial dimensions place stringent demands on a measurement’s sensitivity and range. In this study, we report the simultaneous measurement of all components of this polarization-dependent optical force by using a 3D force spectroscopy technique with femtonewton sensitivity. The vector force fields are compared quantitatively with our theoretical calculations as the polarization state of the incident light is varied and show excellent agreement. By plotting the 3D motion of the Mie particle in response to the switched force field, we offer visual evidence of the effect of spin momentum on the Poynting vector of an evanescent optical field.

In this work, we demonstrate a hybrid scanning tunneling microscope/near field scanning microwave microscope featuring nanometric resolution in liquid environment. The system performs an ultra-broadband microwave analysis, since the frequency is swept (up to 50 GHz) for each spatial point of the sample under measurement. A conversion in time-domain allows to disentangle near-field and far-field probe-sample interactions. Results are reported for highly oriented pyrolitic graphite immersed in water, and demonstrate microwave nanometric resolution in spite of the presence of the losses induced by the aqueous environment.