The resolution of ultrafast studies performed at extreme ultraviolet and X-ray free-electron lasers is still limited by shot-to-shot variations of the temporal pulse characteristics. Here we show a versatile single-shot temporal diagnostic tool that allows the determination of the extreme ultraviolet pulse duration and the relative arrival time with respect to an external pump-probe laser pulse. This method is based on time-resolved optical probing of the transient reflectivity change due to linear absorption of the extreme ultraviolet pulse within a solid material. In this work, we present measurements performed at the FLASH free-electron laser. We determine the pulse duration at two distinct wavelengths, yielding (184 ± 14) fs at 41.5 nm and (21 ± 19) fs at 5.5 nm. Furthermore, we demonstrate the feasibility to operate the tool as an online diagnostic by using a 20-nm-thin Si 3 N 4 membrane as target. Our results are supported by detailed numerical and analytical investigations.

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL)\ud pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial\ud experimental parameter that needs to be characterized. We measured the pulse shape of an extreme\ud ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods\ud based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods,\ud one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities.\ud The measurements were carried out at the seeded FEL facility FERMI. The FEL temporal pulse\ud characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they\ud were compared to the predictions of a theoretical model. The measurements allowed a direct observation of\ud the pulse lengthening and splitting at saturation, in agreement with the proposed theory

Extreme-ultraviolet to x-ray free-electron lasers (FELs) in operation for scientific applications are up to now single-user facilities. While most FELs generate around 100 photon pulses per second, FLASH at DESY can deliver almost two orders of magnitude more pulses in this time span due to its superconducting accelerator technology. This makes the facility a prime candidate to realize the next step in FELs-dividing the electron pulse trains into several FEL lines and delivering photon pulses to several users at the same time. Hence, FLASH has been extended with a second undulator line and self-amplified spontaneous emission (SASE) is demonstrated in both FELs simultaneously. FLASH can now deliver MHz pulse trains to two user experiments in parallel with individually selected photon beam characteristics. First results of the capabilities of this extension are shown with emphasis on independent variation of wavelength, repetition rate, and photon pulse length.

Applications in life sciences and information technology require all-optical solutions. In the inevitable race towards miniaturized optical circuits, all-integrated solutions will prevail against bulk setups. Because of its outstanding nonlinear properties, lithium niobate (LiNbO3) emerged as the key platform for integrated optics. In this paper, we discuss the direct femtosecond (fs) laser inscription technique whose flexibility enables the realization of two- and three-dimensional embedded optical waveguides in various optical materials. Linear and nonlinear components for monolithic and hybrid waveguide devices are characterized and their perspectives are reviewed, e.g. couplers, Bragg reflectors, frequency converters, amplitude modulators and gain modules. Finally, we demonstrate a monolithic LiNbO3 waveguide chip that combines a frequency doubling and a modulating unit. Thumbnail image of Schematic of a hybrid fs laser written chip that comprises a rare-earth-doped laser section (a), a frequency doubling unit (b), Bragg reflectors (c), waveguide splitters (d) and an amplitude modulator (e)