Electrons Laser Diode Controller To Laser Trigger Time to Digital Converter

Computer Figure 1. Schematic of the LBL Pulsed X-ray Facilit. Light from a laser diode excites the photocathode, liberating photoelectrons that are accelerated to the tungsten anode, creating x-rays on impact. The x-rays excite the sample and the resulting fluorescent emissions are detected with a photomultiplier tube and recorded. We have developed a bench-top pulsed x-ray system for measuring scintillation properties of compounds in crystal or powdered form. The source is a light-excited x-ray tube that produces 40 x-ray photons (mean energy 18.5 keV) per steradian in each 100 ps fwhm pulse. The repetition rate is adjustable from 0 to 107 pulses per second. The fluorescent emanations from the x-ray excited samples are detected with either a sapphire-windowed microchannel plate photomultiplier tube (spectral range 150–650 nm, tra sit time jitter 40 ps fwhm) or a quartz windowed GaAs(Cs) photomultiplier tube (spectral range 160–930 nm, transit time jitter 4 ns fwhm). Decay time spectra are acquired using a TDC having 40 ps fwhm resolution over a 84 ms dynamic range. A computer controlled monochromator can be inserted into the optical path to measure the emission spectrum or wavelength resolved decay time spectrum. A computer controlled sample changer allows up to 64 samples to be measured without intervention. can be inserted into the optical path to provide wavelength sel ctivity. A variety of conventional nuclear electronics is used to process the data, including a time to digital converter (TDC) to record the arrival time of the optical signal and a scaler to count the number of pulses observed. All facets of the Facility are under the control of a personal computer. I