Latest Results From Time Resolved Intensity And Polarization Measurements At Mami

At the Institute of Nuclear Physics at Mainz we investigate time resolved intensity and polarization spectra in the photoelectron emission from different types of highly polarized p-type strained layer and superlattice photo cathodes used for polarized electron sources at accelerator facilities. After several improvements concerning time resolution and phase stability the observed response times decreased to 2-2.5ps which is the time resolution of our setup, Obtaining these short response times we decided to reinvestigate the emission process using simpler GaAs structures with different layer thickness, With the new data one may have to reconsider the escape process of the electrons for thin active layers. The:measured response times of about Ips or less for 100-200nm active layer thickness suggest some ballistic traveling of the electrons through the crystal without interaction. For these electrons energy loss and depolarization seem to take place only in the bent band region or on the crystal surface.