The new fiber Fabry-Pérot interferometer integrated to our low temperature atomic force/magnetic force microscope (LT-AFM/MFM) is operating in the 4–300 K temperature range. A multilayer dielectric mirror coated optical fiber is used to achieve unprecedented 1 fm/√Hz noise level, while the shot noise limit is 0.51 fm/√Hz. The cavity length is adjustable, and
the fiber can be brought within a very close proximity of the cantilever using a dedicated 2 mm stroke piezonanopositioner integrated on the piezotube scanner. The same nanopositioner also is used to park the fiber at a safe parking location during cantilever exchange.