Optimization of tapered fiber sample for laser cooling of solids

The physical mechanism of radiation cooling by anti-Stokes fluorescence was originally proposed in 1929 and experimentally observed in solids in 1995 by Epstein's research team in ytterbium-doped ZBLANP glass. Some specific combinations of the ions, host materials, and the wavelength of the incident radiation can provide anti-Stokes interaction resulting in phonon absorption accompanied by the cooling of the host material. Although optical cooling of the Yb3+-doped ZBLANP sample was already observed there are broad possibilities for its improvement to increase the temperature-drop of the sample by optimization of the geometrical parameters of the sample. We propose a theoretical mode for an optimized tapered fiber structure for use as a sample in anti-Stokes laser cooling of solids. This tapered fiber has a fluoroziconate glass ZBLANP with a core doped with Yb3+ or Tm3+ ions. As is evident from the results of this work, the appropriate choice of the fiber core and the fiber cladding radii can significantly increase the temperature-drop of the sample increases with an increase in the pump power. The depletion of the pump power causes a temperature gradient along the length of the cooled sample.