ULTRA LOW NOISE LT-AFM WITH FABRY-PEROT INTERFEROMETER
LOW TEMPERATURE MICROSCOPE
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.
The Fabry interferometer (variable-gap interferometer) was produced in 1897 by the French physicists Charle Fabry. It consists of two highly reflective and strictly parallel plates called an etalon. Because of the high reflectivity of the plates of the etalon, the successive multiple reflections of light waves diminish very slowly in intensity and form very narrow, sharp fringes. These may be used to reveal hyperfine structures in line spectra, to evaluate the widths of narrow spectral lines, and to redetermine the length of the standard meter.
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.
Ultra Low Noise LT-AFM with Fabry-Perot Interferometer’s Basic Principles
The working principle of the Fabry–Pérot interferometer is basically based on the principles of superposition and resonance. Light penetrating into the interferometer from the partially reflecting mirror is reflected between the mirrors. The light that reflects and travels between the mirrors interferes: in this case, the constructive interference of light depends on the wavelength of the light in the interferometer and the distance between the mirrors in the interferometer. In this case, the constructive interference formula can simply be given as:
The Fabry-Pérot interferometer is frequently used in lasers (especially diode lasers and single-mode lasers) to achieve gain medium resonance. Due to their frequency-selective properties, they also have a place for themselves in wavelength division multiplexing systems in fiber optic communication. In optical spectrum analysis, interferometers with adjustable distance are also used to meticulously determine the wavelength of light.