Differential self-mixing interferometry for micro-cantilever motion sensing

Force sensing is a common practice used for the characterization of matter properties and in particular of bio-materials. Different optical methods have been used in the past to allow high resolution force measurements while avoiding uncertainties induced by external loading of contact sensors. In this paper, we propose the use of differential self-mixing interferometry, a self-aligned, cost effective and compact technique that allows the measurement of displacements with a theoretical resolution in the order of λ/2000 and a practical resolution in the order of λ/200 in practical applications. The DSMI sensor is used to detect the motion of a rectangular cross section cantilever placed on a piezoelectric stage. The measurements were compared with the signal received from the internal piezo stage capacitive sensor, which has a nominal resolution of 2 nm . Results show that the DSMI sensor is able to follow accurately the cantilever displacement. A discussion of the potentials, limitations and required further developments of the method will also be presented.