We reconsider the influence of two-particle final state interactions (FSI) on two-particle Bose-Einstein interferometry. We concentrate in particular on the problem of particle emission at different times. Assuming chaoticity of the source, we derive a new general expression for the symmetrized two-particle cross section. We discuss the approximations needed to derive from the general result the Koonin-Pratt formula. Introducing a less stringent version of the so-called smoothness approximation we also derive a more accurate formula. It can be implemented into classical event generators and allows to calculate FSI corrected two-particle correlation functions via modified Bose-Einstein "weights".Comment: 12 pages RevTeX, 2 ps-figures included, submitted to Phys. Rev.

We report on a semiconductor–superlattice frequency multiplier for the generation of submillimeter waves. A monochromatic microwave-pump field (frequency near 100 GHz) periodically excited a superlattice into states of negative differential conductivity giving rise to space-charge domain creation and annihilation joint with a nonsinusoidal high-frequency current and radiation at harmonics of the pump field. A highly doped GaAs/AlAs superlattice allowed the conversion of pump to third-harmonic radiation at 300 GHz with an efficiency of about 1% (power∼30 μW).