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Self-Seed XFEL
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At BL3, a narrow band of XFEL can be used with the reflective self-seed method (figure 1). Self-seed XFEL have the same average pulse energy as SASE XFEL, but exhibit high-monochromaticity. Providing this type of XFEL requires an adjustment time of approximately one shift. In addition, it takes longer than usual to change the wavelength. These adjustment times are included in the user’s beam time. |
If you are planning to use self-seed XFEL, please be sure to contact the このメールアドレスはスパムボットから保護されています。閲覧するにはJavaScriptを有効にする必要があります。 for information on the available wavelength conditions before applying for an assignment. |
References:
I. Inoue et al., Nature Photon. 13, 319 (2019). |
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ー Figure 1: A schematic diagram of the reflective self-seeding method at SACLA. In reflective self-seeding, the undulator is divided into two sections, with a channel-cut crystal made of silicon installed between them. The XFEL oscillated in the first half are monochromatized by this analyzer crystal. Then, by amplifying this monochromatic seed-light with the undulator in the latter half, a narrow band of XFEL is generated. |
Characteristics of self-seed XFEL
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Self-seed XFEL spectrum
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The spectral width (ΔE/E)of the XFEL is approximately 0.03%. This is about one-tenth of the normal operating mode for SACLA. On the other hand, the pulse energy of the self-seed mode is approximately 60% of the normal mode. Figure 2 shows an example of the spectrum of the normal operating mode and the self-seed mode. |
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ー Figure 2: A comparison between the spectrum of normal operation and self-seed operation. |
Fluctuations of the energy width for each shot
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During self-seed operation, the photon energy width of the XFEL pulse is different for each shot. This is due to the fact that the nature of the electron beam varies from pulse to pulse (especially the energy chirp). Figure 3 shows a histogram of the photon energy width for each shot. If spectral width information is required to analyze experimental data, the EH1 single-shot spectrometer can be used to measure the spectrum for each shot in parallel with the experiment. |
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ー Figure 3: A histogram of photon energy width for each pulse of self-seed XFEL (10 keV self-seed XFEL). |
Guidelines for photon energy and pulse energy that can be oscillated
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Photon energy |
7-15 keV |
Energy width |
0.03% |
Pulse energy |
200 µJ @ 7-10 keV, ~100 µJ @ 15 keV |
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