Основы физики. Волновая и квантовая оптика
Light diffraction in a nonuniform acoustic field induced by a wedge shaped piezoelectric trans ducer is theoretically studied. Electric, acoustic, and acoustooptic characteristics of cells with such transducers are calculated. The emphasis is on the features of cell operation in the case when a piezoelectric plate is excited at the third harmonic. The acoustic field is shown to possess a complex amplitude and phase structure varying with the ultrasound frequency. The efficiency of acoustooptic diffraction depending on the acoustic wave amplitude and phase mismatch is studied. It is established that the efficiency of the Bragg diffraction can approach 100% despite a noticeable phase mismatch. Optimal values for the ultrasound power and angles of light incidence onan acoustooptic cell are found.
A linear theory of the discrete interaction of electron beams and electromagnetic waves in slow-wave structures (SWS) is developed. The theory is based on the finite_difference equations of SWS excitation.The local coupling impedance entering these equations characterizes the field intensity excited by the electron beam in interaction gaps and has a finite value at SWS cutoff frequencies. The theory uniformly describes the electron–wave interaction in SWS passbands and stopbands without using equivalent circuits, a circumstance that allows considering the processes in the vicinity of cutoff frequencies and switching from the Cerenkov mechanism of interaction in a traveling wave tube to the klystron mechanism when passing to SWS stopbands. The features of the equations of the discrete electron–wave interaction in pseudoperiodic SWSs are analyzed.