Theory of the laser diode interaction in scanning force microscopy

The theory of interaction of a vibrating cantilever and a laser diode used in a scanning force microscope is given in terms of a feedback-dependent parameter C, which determines the gain associated with the interaction. It is shown that both C and the amplitude of the vibrations can be determined experimentally from the measurement of the first and second harmonics. Experimental results, which are in good agreement with the theory, yield a value for C of 0.045. Under these weak feedback conditions, it is found that the interaction can be modeled approximately as a simple homodyne process.>