Changes in Floquet-state structure at avoided crossings: Delocalization and harmonic generation

Avoided crossings are common in the quasienergy spectra a of strongly drive n nonlinear quantum wells. In this paper we examine the sinusoidally driven particle in a square potential well to show that avoided crossings can alt er the structure of Floquet states in this system. Two types of avoided cro ssing!, an identified: one type leads only to temporary changes las a funct ion of driving field strength in Floquet state structure: while the second type can lead to permanent delocalization of the Floquet states. Radiation spectra from these latter states show a significant increase in high harmon ic generation as the system passes through the avoided crossing. [S1050-294 7(99)03504-0].