Useful transformations: from ion-laser interactions to master equations
  We show set of transformations which allow to obtain analytic solutions in several quantum-optical problems. We start with the ion-laser (time dependent) interaction, continue with the problem of a slow atom interacting with a quantized field to end with a master equation that describes losses. In all cases it is shown that one may find useful transformations that simplify the problems. 
R. Ju\'arez-Amaro, J.M. Vargas-Mart\'inez and H. Moya-Cessa