Advanced holeburning techniques for determination of hyperfine   transition properties in inhomogeneously broadened solids applied to   Pr3+:Y2SiO5
  A sequence of optical holeburning pulses is used to isolate transitions between hyperfine levels, which are initially buried within an inhomogeneously broadened absorption line. Using this technique selected transitions can be studied with no background absorption on other transitions. This makes it possible to directly study properties of the hyperfine transitions, e.g. transition strengths, and gives access to information that is difficult to obtain in standard holeburning spectroscopy, such as the ordering of hyperfine levels. The techniques introduced are applicable to absorbers in a solid with long-lived sublevels in the ground state and where the homogeneous linewidth and sublevel separations are smaller than the inhomogeneous broadening of the optical transition. In particular, this includes rare-earth ions doped into inorganic crystals and in the present work the techniques are used for spectroscopy of Pr3+ in Y2SiO5. New information on the hyperfine structure and relative transition strengths of the 3H4 - 1D2 hyperfine transitions in Pr3+:Y2SiO5 has been obtained from frequency resolved absorption measurements, in combination with coherent and incoherent driving of the transitions. 
Mattias Nilsson, Lars Rippe, Robert Klieber, Dieter Suter, Stefan   Kroll