Study of laser-induced self-oscillations in silicon nanomechanical resonators

We report a study of laser-induced oscillation of nanomechanical resonators. The modes of motion of single-stage and double-stage paddle resonators are first assessed using finite element analysis and experimentally observed using piezoelectric actuation of the devices. The flexural modes of the same devices are then excited at resonance using laser-induced thermal effects. As the actuating power is gradually increased, the resonators experience three phases of resonance characterized by distinct changes of amplitude and number of peaks observed. In addition, the resonant frequencies initially show a steady decrease with actuating power followed by a distinct increase. Finally, a sharpening of the resonant response is also observed as actuating power is increased. However, such peak sharpening is also accompanied by instabilities of the center frequency. These instabilities could be induced by a frequency mismatch between the parametric actuation mechanism and the natural resonance of the device, or by optically induced temperature fluctuations along the length of the resonator supports.