Abstract: A method of measuring an ac force by a scanning probe system is proposed.The lever of the system is driven by the ac force between the sample and the tip of the lever,so that the ac force can be determined by the amplitude of the vibration of the lever,which is measured by a heterodyne laser interferometer. The variation of the force with the distance between the sample and the tip,and the electric and magnetic fields are deteeted.The thickness of thin films is measured,The force detection sensitivity is also discussed and is estimated to be about 10^-11 N.

Key words: scanning peobe, ac force, heteodyne laser interferometer