To measure the shape of the sample, the electromagnets are energized to pull the AFM head backward.
However, this sample has a sloped ridge at its center. As the probe tip runs up the edge of this ridge, the cantilever is bent even more strongly. And as it bends, the reflected laser beam moves to the back of the photodetector.
But now the electronic feedback loops kick in. By further energizing the top electromagnet, they rotate the invisible tripod (laser, cantilever and photodetector) upward. This continues until the cantilever straightens out enough to return the reflected laser to the center of the photodetector.
