Modeling Streak Camera Sweep Speeds

On the OMEGA laser system at the University of Rochester's Laboratory for Laser Energetics (LLE), six P5 10 streak cameras measure the pulse shape of the 60 OMEGA beam lines. These cameras use a photocathode to convert an optical signal into an electron beam. A voltage ramp then sweeps this electron beam across a phosphor screen which is in turn imaged by a CCD. Currently, 120 images of an eight-pulse fiducial laser with a period of 548 ps are used to obtain approximately 700 measurements of the speed at whch the electron beam sweeps across the image (sweep speed). A spline interpolation is then used to obtain sweep speed values at all points on the CCD. Unfortunately, this introduces noise, and fails when the sweep window changes due to unexpected variations in the camera's voltages. In order to deal with these issues, a model was constructed using frequencies obtained from a PSPICE simulation of the camera's sweep circuitry. This model will replace the spline interpolation, yielding a more accurate sweep and allowing data recovery in case of malfunction. Introduction Streak cameras are instruments which convert optical signals into images where time is mapped to spatial displacement. They are extremely useful in measuring many types of short duration optical phenomena.' As a result, their uses are extremely varied. Their basic construction, however, is largely the same regardless of their use. First, a photocathode is exposed to the optical signal to be measured, causing the photocathode to emit a beam of electrons (see fig. 1). The number of electrons emitted is proportional to the intensity of the input signal. This electron beam is then accelerated through a potential difference and focused between two plates which have a changing voltage across them. This changing voltage has the effect of changing the electron beam's deflection over time. Finally, at the end of the system, the electron beam impacts on a phosphor screen which fluoresces. The fluorescence is then imaged onto some medium. The image created has two special characteristics. First, movement across the image represents a change in time, a reflection of the fact that the electron beam moved across the phosphor screen during the exposure. Second, wlndow