Analytical modeling of micromachined resonator sensor activated by cw laser irradiation

Analytical modeling of micromachined mechanical resonator sensor self-excited by cw laser irradiation is presented. The optical feedback through the photothermal effect in the interference fringe generates the self-excited vibration of the micromachined beams. The optical interference, thermal diffusion in the resonator and mechanical dynamics of the resonator are combined to maintain the oscillation. From the analysis, the following phenomena of the self-excited vibration have been explained: (1) threshold in light intensity to generate the vibration, (2) saturation of the vibration amplitude, (3) periodicity of the vibration excitation as a function of the displacement of the feedback mirror, (4) bistability of the vibration center, and (5) frequency shift of the vibration.