In accordance with one aspect of the present invention, a cantilever of a probe-based instrument is deflected by directing a beam of ultrasonic acoustic energy at the cantilever to apply acoustic radiation pressure to the cantilever. The energy is generated by an acoustic actuator. The transmitted beam preferably is focused using a cylindrical lens, providing a beam tightly focused in one dimension and unfocused in a second dimension. In accordance with another aspect of the present invention, a power source such as an RF signal generator is operated so as to spread the spectrum of acoustic radiation on a time scale that is short or comparable to the acoustic roundtrip time. Such a design diminishing the resonance effects and sensitivity to spacing between the cantilever and the acoustic source.