reflected on the surface of the two dimensional psd oriented orthogonally with respect to the reflected ray a conventional arrangement of the elements for measuring optical beam deflection is schematically shown a light source 1 usually a laser emits a light beam 2 focused directly or by means of using intermediate optical elements such as mirrors on the mechanical structure 3 the displacement of which is to be measured for example on the end of a cantilever 3 the fixed end of the cantilever 3 is anchored to a piezoelectric actuator 7 deflection of the reflected beam 5 is preferably measured with an orthogonal psd 4 but a segmented photodetector a continuous position detecting photodetector an array of photodetectors etc could also be used therefore a coordinate system where the x y plane is the plane of the surface of the microcantilever 3 and x and v are along the scanning directions of the beam 2 is first defined therefore out of plane displacement of the cantilever 3 occurs along the z axis the incident beam 2 is in the x z plane and the photodetector 4 is oriented with an axis along the y direction with this configuration photocurrents along the axes of the photodetector 4 determined by the coordinates of the reflected laser beam 5 in the photodetector 4 are linearly proportional to the slope of the cantilever 3 along the x and y directions in the point of reflection 6 in turn in order for the beam 2 to scan the surface of the cantilever 3 it has been envisaged that the piezoelectric actuator 7 is fixed to a first.