Development of a pump-probe facility with sub-picosecond time resolution combining a high-power ultraviolet regenerative FEL amplifier and a soft X-ray SASE FEL

This paper presents the conceptual design of a high power radiation source with laser-like characteristics in the ultraviolet spectral range at the TESLA Test Facility (TTF). The concept is based on the generation of radiation in a regenerative FEL amplifier (RAFEL). The RAFEL described in this paper covers a wavelength range of 200–400 nm and provides 200 fs pulses with 2 mJ of optical energy per pulse. The linac operates at 1% duty factor and the average output radiation power exceeds 100 W. The RAFEL will be driven by the spent electron beam leaving the soft X-ray FEL, thus providing minimal interference between these two devices. The RAFEL output radiation has the same time structure as the X-ray FEL and the UV pulses are naturally synchronized with the soft X-ray pulses from the TTF FEL. Therefore, it should be possible to achieve synchronization close to the duration of the radiation pulses (200 fs) for pump-probe techniques using either an UV pulse as a pump and soft X-ray pulse as a probe, or vice versa

Experience with MCP-based Photon Detector at FLASH2

We present recent experimental results on statistical measurements of amplification process in FLASH2 SASE FEL. Micro-channel plate (MCP) detector is used for precise measurements of the radiation pulse energy. DAQ based software is used for cross-correlation of the SASE FEL performance and electron beam jitters. Analysis of machine jitters essential for SASE FEL operation has been performed. Application of gating strategy with measured machine parameters allows us to isolate machine jitters from fundamental SASE fluctuations. Subsequent application of statistical techniques for characterization of SASE FEL radiation allows to derive such important quantities as gain length, saturation length, radiation pulse duration, coherence time, and degree of transverse coherence

Single-shot determination of focused FEL wave fields using iterative phase retrieval

Determining fluctuations in focus properties is essential for many experiments at Self-Amplified-Spontaneous-Emission (SASE) based Free-Electron-Lasers (FELs), in particular for imaging single non-crystalline biological particles. We report on a diffractive imaging technique to fully characterize highly focused, single-shot pulses using an iterative phase retrieval algorithm, and benchmark it against an existing Hartmann wavefront sensor. The results, both theoretical and experimental, demonstrate the effectiveness of this technique to provide a comprehensive and convenient shot-to-shot measurement of focused-pulse wave fields and source-point positional variations without the need for manipulative optics between the focus and the detector

THz SASE FEL at PITZ: lasing at a wavelength of 100µm

Development of an accelerator-based tunable THz source prototype for pump-probe experiments at the Eu-ropean XFEL is ongoing at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The proof-of-principle exper-iments on the THz SASE FEL are performed utilizing the LCLS-I undulator installed in the PITZ beamline. The first lasing at a center wavelength of 100 µm was ob-served in the summer of 2022. The lasing of the narrow-band THz source was achieved using an electron beam with an energy of ~17 MeV and a bunch charge up to several nC. Optimization of beam transport and matching resulted in the measurement of THz radiation with a pulse energy of tens of µJ, measured with pyroelectric detectors. The THz FEL gain curves were measured by means of specially designed short coils along the undulator. The results of the first characterization of the THz source at PITZ will be presented

Lasers and Coherent Light Sources

This chapter describes lasers and other sources of coherent light that operate in a wide wavelength range. First, the general principles for the generation of coherent continuous-wave and pulsed radiation are treated including the interaction of radiation with matter, the properties of optical resonators and their modes as well as such processes as Q-switching and mode-locking. The general introduction is followed by sections on numerous types of lasers, the emphasis being on todayʼs most important sources of coherent light, in particular on solid-state lasers and several types of gas lasers. An important part of the chapter is devoted to the generation of coherent radiation by nonlinear processes with optical parametric oscillators, difference- and sum-frequency generation, and high-order harmonics. Radiation in the extended ultraviolet (EUV) and x-ray ranges can be generated by free electron lasers (FEL) and advanced x-ray sources. Ultrahigh light intensities up to 1021 W/cm2 open the door to studies of relativistic laser–matter interaction and laser particle acceleration. The chapter closes with a section on laser stabilization

Coherent-Pulse 2D Crystallography Using a Free-Electron Laser X-Ray Source.

Coherent diffractive imaging for the reconstruction of a two-dimensional (2D) finite crystal structure with a single pulse train of free-electron laser radiation at 7.97 nm wavelength is demonstrated. This measurement shows an advance on traditional coherent imaging techniques by applying it to a periodic structure. It is also significant that this approach paves the way for the imaging of the class of specimens which readily form 2D, but not three-dimensional crystals. We show that the structure is reconstructed to the detected resolution, given an adequate signal-to-noise ratio

Opportunities for two-color experiments in the soft X-ray regime at the European XFEL

Abstract X-ray pump/X-ray probe applications are made possible at X-ray Free Electron Laser (XFEL) facilities by generating two X-ray pulses with different wavelengths and controllable temporal delay. In order to enable this capability at the European XFEL, an upgrade project to equip the soft X-ray SASE3 beamline with a magnetic chicane is underway. In the present paper we describe the status of the project, its scientific focus and expected performance, including start-to-end simulations of the photon beam transport up to the sample, as well as recent experimental results demonstrating two-color lasing at photon energies of 805 eV + 835 eV and 910 eV + 950 eV. Additionally, we discuss methods to analyze the spectral properties and the intensity of the generated radiation to provide on-line diagnostics for future user experiments