Pyrene-Naftylamide Bifluorophore for Spectra-Converting Media

New bifluorophore containing pyrene as an excitation energy donor and naphtylamide as an acceptor is synthesized and its optical properties are studied. It is founded that excitation spectrum of the bifluorophore is almost the sum of its constituents—pyrene and naftylamide. At the same time, in the luminescence spectrum there only the peak of acceptor luminescence is observed, which indicates the effective radiationless energy transfer from the donor to the acceptor. This is also proved by time resolved measurements of bifluorophore decay. The decay rate was calculated from decay curve and appear to be 0.25 нс^?1. The same value obtained from the Förster’s theory is almost by an order as high. It indicates that Förster’s does not applicable in this particular case. Instead, we have to use the electron excitation density functions approach.     

The Nature of Trapping Centers in Amorphous Biphenyl-Containing Polymer

Study of optical properties of methyl methacrylate and 4-vinylbiphenyl copolymers in a rigid amorphous polymer allowed establishing the non-excimer nature of energy traps in a polymer chain. These traps are probably related to possibility of collective states formed by macromolecule’s chromophore groups. The shortening of the trap states decay time in 4-vinylbiphenyl homopolymer comparing to copolymer is observed.     

Subpicosecond electro-optic measurement of relativistic electron pulses

Time-resolved measurements of the transverse electric field associated with relativistic electron bunches are presented. Using an ultrafast electro-optic sensor close to the electron beam, the longitudinal profile of the electric field was measured with subpicosecond time resolution and without time-reversal ambiguity. Results are shown for two cases: inside the vacuum beam line in the presence of wake fields, and in air behind a beryllium window, effectively probing the near-field transition radiation. Especially in the latter case, reconstruction of the longitudinal electron bunch shape is straightforward.