New approach to jitter reduction of an x-ray streak camera in accumulation mode. Page: 2 of 6
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which is significantly better than a similar camera with slower switch and deflection plates.[61
2. METHODS OF REDUCING TIMING JITTER
The streak tube that was used in this work is similar to our previous design[9'10 except that we redesigned the deflection
plates. In the streak tube, the x-ray-produced electrons from the photocathode are accelerated by the high field (10
kV/mm) between the photocathode and the anode. The electrons then enter the region between a pair of deflection plates.
The deflection plates are driven by a ramp voltage produced by a photoconductive switch that will be described later.
Finally, the electrons are focused on the microchannel plate /phosphor screen by a magnetic lens. It is well known that
the temporal resolution of streak camera are limited mainly by the transit time dispersion of the photoelectrons as they
travel from the photocathode to the deflection plates. It is also limited by the spatial resolution of the electron optics in
the tube and by the sweeping speed. It was demonstrated before that the contribution from these two factors is about 0.5
ps for a previously developed camera. []
When the camera operates in the accumulation mode, the dominating factor that limits the time resolution is the timing
jitter. While the response time of the photoconductive switch to the triggering laser may be instantaneous, the timing
jitter is not zero unless the laser pulse is absolutely stable. At the present, the lasers used in synchrotron facilities for
time-resolved x-ray studies are Ti:sapphire lasers operated at kilohertz repetition rate. The same laser is used to pump the
sample under investigation and to trigger the photoconductive switch. The pulse energy fluctuation is on the order of 1 %
rms. This energy fluctuation causes the output amplitude of the photoconductor to change from shot to shot, which in
turn produces timing jitter.
The timing jitter caused by laser fluctuation is illustrated in Figure 1, where the time dependence of the output amplitude
of the switch from two laser shots is shown. We assume that the first pulse (V1) has higher amplitude than the (V2). If
properly calibrated, it will take a longer time for the second pulse to reach a certain level of driving voltage (for example,
at half of the averaged pulse high, Va), which corresponds to the center of the phosphor screen. The time difference (t2-tl)
represents the time jitter due to the switch response to the fluctuation of laser intensity. The jitter of the switch can be
simply expressed as
AV
Atptter = s0.5T,,e V - (1)
Where TRiS, is the rise time of sweeping pulse, AV/Va is the rms fluctuation in the shot-to-shot switch output
voltage, which is related to the laser intensity fluctuation nonlinearly (if the switch is operated in a saturated mode
to suppress the effect of the laser intensity fluctuation). Therefore, the jitter can be reduced by decreasing the rise
time.
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Liu, J.; MacPhee, A. G.; Liu, C.; Shan, B.; Wang, J. & Chang, Z. New approach to jitter reduction of an x-ray streak camera in accumulation mode., article, July 19, 2002; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc737028/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.