Theory of Multiphoton Processes : Springer : 9780306423178 : 0306423170 : 31 May 1987 : My aim in this book has been to give an account of the theoretical methods of analysis of multiphoton processes in atomic physics. In this account I have emphasized systematic methods as opposed to ad hoc approaches. Both perturbative and nonperturbative methods are presented with il­ lustrative results of concrete applications. The perturbation theory is the primary tool of analysis of nonresonant multiphoton processes. It is developed here in conjunction with a diagrammatic language and is also renormalized to free it from the unwanted divergences which accompany the ordinary treatment when higher-order corrections are considered. The nonperturbative methods (i.e., methods other than that of power series ex­ pansion in the field strength) become particularly important for consistent treatments of problems involving, for example, intermediate resonances, high field strengths, and finite pulse durat