Removing interference and optical feedback artifacts in atomic force microscopy measurements by application of high frequency laser current modulation

Atomic force microscopy measurements based on optical beam deflection can seriously be affected by two specific types of artifacts. Disturbances of the first type are caused by interference on the quadrant photodiode between the beam reflected directly from the cantilever and stray light from the sample surface. The second type is optical feedback effects caused by light scattering from the surface back into the laser cavity. We demonstrate that both types can be significantly reduced by application of high frequency laser current modulation. Residual noise is dominated by electronic and mechanical noise, shot noise, and noise caused by the thermal motion of the cantilever.