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Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

Single-pass free-electron lasers based on self-amplified spontaneous emission1,2,3,4 are enabling the generation of laser light at ever shorter wavelengths, including extreme ultraviolet5, soft X-rays and even hard X-rays6,7,8. A typical X-ray free-electron laser is a few kilometres in length and requires an electron-beam energy higher than 10 GeV (refs 6, 8). If such light sources are to become accessible to more researchers, a significant reduction in scale is desirable Here, we report observations of brilliant extreme-ultraviolet radiation from a 55-m-long compact self-amplified spontaneous-emission source, which combines short-period undulators with a high-quality electron source operating at a low acceleration energy of 250 MeV. The radiation power reaches saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ. The ultralow emittance (0.6π mm mrad) of the electron beam from a CeB6 thermionic cathode9 is barely degraded by a multiple-stage bunch compression system that dramatically enhances the beam current from 1 to 300 A. This achievement expands the potential for generating X-ray free-electron laser radiation with a compact 2-GeV machine. Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.

We achieved stable operation of a free-electron laser (FEL) based on the self-amplified spontaneous-emission (SASE) scheme at the SPring-8 Compact SASE Source (SCSS) test accelerator in the extremely ultraviolet region. Saturation of the SASE FEL power has been achieved at wavelengths ranging from 50 to 60 nm. The pulse energy has reached $\ensuremath{\sim}30\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ at 60 nm. The observed fluctuation of the pulse energy is about 10% (standard deviation) for several hours, which agrees with the expectation from the SASE theory showing the stable operation of the accelerator. The SASE FEL has been routinely operated to provide photon beams for user experiments over a period of a few weeks. Analysis on the experimental data gave the normalized-slice emittance at the lasing part is around $0.7\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$. This result indicates that the normalized-slice emittance of the initial electron beam, $0.6\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ in a 90% core part, is kept almost unchanged after the bunch compression process with a compression factor of approximately 300. The success of the SCSS test accelerator strongly encourages the realization of a compact XFEL source.

We have developed a high‐speed and simultaneous photon beam diagnostic system using optical cables at SPring‐8. The system is composed of blade type X‐ray beam position monitors (XBPM) in front ends, optical cables spread over the experimental hall and multi A/D converters at the photon beam diagnostic station. Analog data of the beam positions are transferred through the optical cables. The multi A/D converter allows us to browse and process the data from the main control room in real time. The features of the system are the wide band‐width, the ability of full‐time observation with XBPMs and the compatibility to the monitoring system of electron beam position monitors in the storage ring. The system has been routinely used for high‐speed and simultaneous measurements of photon beam and electron beam.

This paper describes a CdTe pixel detector development for high energy diffraction experiments at SPring-8. A second prototype detector (SP8-02) was designed with a pixel size of 200 μm ×200 μm and a matrix of 20 × 50. The sensor is bonded to an ASIC with a preamplifier, a shaper, a window-type discriminator and a 20-bits counter in each pixel. The current-voltage characteristics verified that a Pt/CdTe/Al-pixel sensor functioned as an electron-collecting diode pixel detector. This type sensor showed a long-term stability at near room temperature.