Updated:
06.08.2011
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The FEMTO group at the Swiss Light Source seeks to create a
facility for femtosecond x-ray/laser pump probe experiments using
electron-beam
slicing. As a part of reaching this goal, the group
also performs active research
in ultrafast x-ray science, using both the femtosecond source and
other means.
Status
The source is operational and is currently being used to perform
experiments.
Research groups interested in a collaboration are encouraged to
contact Gerhard Ingold for a discussion on the technical feasibility of the proposed experiment. If possible, try to formulate some answers to this short list of questions to help start this discussion.
Please DO NOT submit a proposal for beamtime using the FEMTO facility
without first contacting us and discussing the technical feasibility.
This includes any use of the laser system,
even if not using the slicing source. This applies even if you have
submitted proposals in the past, since the parameters of the facility tend to evolve with time.
Source Parameters
The femtosecond sliced x-rays are generated at the microXAS
beamline, at straight 5L of the SLS. Many of the capabilities
(e.g. focusing) of this beamline can be carried over to femtosecond
operation. The table below lists some
of the key properties of the sliced beam.
| Energy range (tuning curves) |
4.2 - 14 keV |
| Flux |
4 x 105 ph/s/0.1% BW (at 5 keV) |
| Bandwidth options (standard) |
Full spectrum, 1.3%, 0.045%, 0.015% (other options possible with special optics) |
| Pulse duration (measured) |
< 120 fs |
| Repetition rate |
2 kHz |
| Polarization |
linear horizontal |
| Energy resolution (with
Si(111) monochromator) |
0.02% |
| Halo background (monochromatic, at 6keV) |
< 4 x 10-2 |
| Core background (monochromatic, at 6keV) |
< 10-3 |
Table 1 Source specifications.
Some definitions of terms:
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Halo background
The x-rays created by the electrons modulated from previous
interactions between the laser and electron beam. The time for one
revolution about the SLS is approximately 1 microsecond, and the
time it takes for modulated electrons to relax back into the normal
electron orbit is several milliseconds.
The time structure of these "old" modulated electrons depends on the number of round trips, but ranges from several hundred
femtoseconds (after one round trip) to about 70 picoseconds.
The background is reported as the ratio of the estimated intensity of the x-rays from the modulated electrons generated by the previous laser pulses to the intensity of the freshly sliced femtosecond pulse, integrated over 10 ns in time.
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Core background
The x-rays from the unmodulated electron beam. This radiation is suppressed by a system of slits in the beamline, but due to its high intensity some small amount contributes to a background of the femtosecond pulse. The reported background is the ratio of this core contribution to the sliced intensity, integrated over about 10 ns in time.
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