Multiphoton transition probabilities for potassium in strong parallel microwave and static fields

We refine an earlier method for calculating the spectra of atoms and molecu les in a strong microwave or laser field plus a static electric field. Resu lts are reported for microwave resonance transition spectra of potassium fo r transitions from the 19s state at five choices of fixed microwave field s trength (38, 68, 120, 152 and 193 V cm(-1)) as the static field strength is varied from 200 to 550 V cm(-1). More resonances have been found in the hi gher microwave field-strength theoretical spectra than previously found exp erimentally. An understanding of butterfly like structures in the plot of q uasi-energy against static electric field strength has allowed an improved understanding of these novel features.