Fabry-perot resonator and system for measuring and calibrating displacement of a cantilever tip using the same in atomic force microscope

A system for measuring a displacement of a tip of a cantilever using a Fabry-Perot resonator in an atomic force microscope, comprising:

• a cantilever having an upper side of a reflective surface and having a lower side with a tip for touching a sample, for moving in a Z-axis direction along with a head body by interlocking a piezoelectric element fixed at a column of an atomic force microscope;
• an optical fiber having one end connected to a light source for irradiating a laser beam, and the other end of a concave mirror shape apart from the reflective surface of the cantilever by a predetermined distance;
• an optical detector for detecting a signal reflected at the end of the concave mirror shape of the optical fiber through a directional coupler positioned at a predetermined location of the optical fiber and a signal incident through the end of the concave mirror shape of the optical fiber after being reflected at the reflective surface of the cantilever;
• and
• a signal processor for calculating an error signal proportional to a displacement of the cantilever from the signals detected from the optical detector, and thereby obtaining a variation in a distance between the end of the concave mirror shape of the optical fiber and the reflective surface of the cantilever.

A system for calibrating a displacement of a tip of a cantilever using a Fabry-Perot resonator in an atomic force microscope, comprising:

• a cantilever having an upper side of a reflective surface and having a lower side with a tip for touching a sample, for moving in a Z-axis direction along with a head body by interlocking a piezoelectric element fixed at a column of an atomic force microscope;
• an optical fiber having one end connected to a light source for irradiating a laser beam, and the other end of a concave mirror shape apart from the reflective surface of the cantilever by a predetermined distance;
• an optical detector for detecting a signal reflected at the end of the concave mirror shape of the optical fiber through a directional coupler positioned at a predetermined location of the optical fiber and a signal incident through the end of the concave mirror shape of the optical fiber after being reflected at the reflective surface of the cantilever;
• a signal processor for calculating an error signal proportional to a displacement of the cantilever from the signals detected from the optical detector, obtaining a variation in a distance between the end of the concave mirror shape of the optical fiber and the reflective surface of the cantilever, and generating a feedback signal for keeping the distance therebetween constant;
• and
• a servo circuit part for moving the cantilever and the optical fiber in a Z-axis direction by actuating the piezoelectric element by the feedback signal generated from the signal processor, so that the distance between a sample and the tip of the cantilever is kept constant.