Time-resolved fluorescence using synchrotron radiation excitation:
A powered fourth-harmonic cavity improves pulse stability
Krzysztof Polewski, Stephen L. Kramer, Zbigniew S. Kolber,
John G. Trunk, Denise C. Monteleone and John C. Sutherland
Rev. Sci. Instr. 65(8), 2562-2567 (1994).
Abstract
The pulsed nature or "time structure" of synchrotron radiation from electron
storage rings is used to measure the kinetics of the decay of electronically
excited states and is particularly useful because the wavelength of excitation
can be chosen at will. However, changes in the length of the pulses of
radiation from a storage ring resulting from the gradual decrease of current
circulating in the ring during the course of a "fill" limit the duration of
data collection, and hence photometric sensitivity. A fourth-harmonic cavity
that was recently added to the vacuum ultraviolet (VUV) storage ring at the
National Synchrotron Light Source slows the loss of current during a fill,
and thus increases the total number of photons produced. When operated in a
passive (unpowered) mode, however, the fourth-harmonic cavity increases both
the average width of the photon pulses and the changes in width that occur
during a fill, thus reducing the usefulness of the VUV ring in timing
experiments. We demonstrate that operating the fourth-harmonic cavity in an
active (powered) mode, while further increasing pulse duration, can stabilize
pulse width, thereby restoring timing capabilities.
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