Wide-Dynamic-Range Cantilever Magnetometry Using a Fiber-Optic   Interferometer and its Application to High-frequency Electron Spin Resonance   Spectroscopy
  We present a method of broadening the dynamic range of optical interferometric detection of cantilever displacement. The key idea of this system is to use a wavelength-tunable laser source. The wavelength is subject to proportional-integral control, which is used to keep the cavity detuning constant during a measurement. Under this control, the change in wavelength is proportional to the cantilever displacement. Using this technique, we can measure large displacements ($>1\ \mathrm{\mu m}$) without degradation of sensitivity. We apply this technique to high-frequency electron spin resonance spectroscopy and succeed in removing an irregular background signal that arises from the constantly varying sensitivity of the interferometer. 
Hideyuki Takahashi, Tsubasa Okamoto, Eiji Ohmichi, Hitoshi Ohta
physics.ins-det