Abstract
Two types of optical choppers for time-resolved measurements at synchrotron radiation soft X-ray beamlines have been developed. One type uses an air-spindle-type rotation mechanism with a two-stage differential pumping system to maintain the ultra-high vacuum of the X-ray beamline, and the other uses a magnetic bearing. Both can be installed at the soft X-ray beamlines at SPring-8, greatly improving the accessibility of pump-and-probe spectroscopy. The combination of X-ray chopper and pump-and-probe photoemission electron microscope at SPring-8 provides drastic improvements in signal-to-noise ratio and resolution compared with techniques using high-voltage gating of channel plate detectors. The choppers have the capability to be used not only at synchrotron radiation facilities but also at other types of soft X-ray and VUV beamlines.
Highlights
Pump-and-probe time-resolved measurements using pulsed light are a recent trend in a variety of scientific fields, and ultra-fast measurements using laser pulses can access the attosecond timescale region
There is no provision of a single-bunch mode, since the reduced average photon flux would impact the experiments of users not performing time-resolved measurements
We have developed two types of X-ray beam chopper suitable for pump-and-probe studies at the soft X-ray beamlines at SPring-8
Summary
Pump-and-probe time-resolved measurements using pulsed light are a recent trend in a variety of scientific fields, and ultra-fast measurements using laser pulses can access the attosecond timescale region. One is to construct gating circuits for the pulse-counting system, as used in previous works (Fukumoto et al, 2008; Kinoshita et al, 2012; Ohkochi et al, 2012), and another is to use a detector system with sufficient time-resolution (Yamamoto & Matsuda, 2013) Another approach is to select single X-ray pulses using. The chopper shape is a disc, and the X-rays pass through grooves cut along radial lines on the surface of the disc, as shown, where a design which can operate at two different repetition frequencies is shown. By changing the position of the grooves relative to the X-ray axis (above or below the broken line in the figure), different repetition frequencies can be selected This grooved design is of low fabrication cost, and is well suited to high-choppingfrequency applications which require large numbers of grooves. This operation is suitable for investigating relatively slow phenomena, in the several microsecond to sub-millisecond range
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