Applications of a High Sensitivity Imaging Photomultiplier Tube to Optical Spectroscopy.

A high sensitivity data acquisition system incorporating a microchannel plate/resistive anode imaging detector has been constructed and used to carry out a series of experiments in optical spectroscopy. The ultra-weak ("green") photoluminescence produced as a result of two electron-two hole recombination in free and bound excitonic systems in silicon has been studied. The results have provided the first experimental evidence for the existence of free polyexcitons (n > 2 e-h pairs). The binding energies of the triexciton (n = 3) and quatraexciton (n = 4) were found to be 3.83 and 6.34 meV respectively. The results of green photoluminescence experiments involving Si:P, Si:Li and Si:B bound multiexciton complexes are also reported. A triple spectrometer of novel design has been constructed and used together with the data acquisition system in a Raman scattering investigation of the high temperature superconductor EuBa_2Cu _3O_{rm 7-x}. A lattice dynamics model has been used to interpret the results and to assist in assigning symmetries to the observed Raman modes. The detector was also incorporated with standard time correlation circuitry to produce a system combining the detectors imaging capabilities with simultaneous subnanosecond time resolution. The power of this system is demonstrated by its application to resonantly excited photoluminescence experiments involving GaAs. Extensions to this system are discussed.