Kai Tiedtke - Academia.edu (original) (raw)

Papers by Kai Tiedtke

Journal of Synchrotron Radiation, 2019

The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissF... more The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissFEL has been measured with an X-ray gas monitor from DESY and compared with a PSI gas detector upstream of the optical components. The transmission efficiencies of the Mo, Si and SiC mirror coatings of the Aramis beamline and the various other in-beam components were evaluated and compared with theoretical calculations, showing an agreement of 6% or better in all cases. The experiment has also shown the efficacy of the high-harmonic rejection mirrors at the Bernina branch of the Aramis beamline at SwissFEL, and characterized the transmission efficiency of the on-line spectrometer in the Aramis beamline. The theoretical transmission of the mirror coatings match the experimental data to within 7%. The accuracy of these measurements was checked against a radiative bolometer from a Japanese collaboration and found to agree to a level of 4% or better. Further comparisons with a diamond detecto...

Nature Photonics, 2020

In the version of this Article originally published, the surname of the author N. Johansson was m... more In the version of this Article originally published, the surname of the author N. Johansson was misspelled as 'Johannson'. In addition, in affiliation 17, "University of Łódź" was incorrect; it should have read "Łódź University of Technology". These errors have been corrected in the online versions of the Article and its Supplementary Information.

Cornell University - arXiv, Jun 23, 2022

We present real-world data processing on measured electron time-of-flight data via neural network... more We present real-world data processing on measured electron time-of-flight data via neural networks. Specifically, the use of disentangled variational autoencoders on data from a diagnostic instrument for online wavelength monitoring at the free electron laser FLASH in Hamburg. Without a-priori knowledge the network is able to find representations of single-shot FEL spectra, which have a low signal-to-noise ratio. This reveals, in a directly human-interpretable way, crucial information about the photon properties. The central photon energy and the intensity as well as very detector-specific features are identified. The network is also capable of data cleaning, i.e. denoising, as well as the removal of artefacts. In the reconstruction, this allows for identification of signatures with very low intensity which are hardly recognisable in the raw data. In this particular case, the network enhances the quality of the diagnostic analysis at FLASH. However, this unsupervised method also has the potential to improve the analysis of other similar types of spectroscopy data. Motivation SASE-FEL challenge Free electron lasers (FEL) enable atomic and molecular science in the femtosecond to attosecond regime by creating highly intense photon pulses on that time scale. However, FELs which are based on the principle of self-amplified spontaneous emission (SASE) [1, 2], such as FLASH [3], produce spatial, spectral and temporal pulse properties that are strongly fluctuating from pulse to pulse. Hence, a reliable photon diagnostic on a single-shot basis is essential for sound data analysis of scientific user experiments performed at such facilities. Post-experiment sorting of recorded data with respect to different properties, such as intensity or wavelength, can reveal signatures of physical processes otherwise obscured or even hidden in the data sets. A number of diagnostic instruments at FELs are used to measure the photoionisation of gas targets, such as the Gas Monitor Detector (GMD) [4, 5] for measurement of absolute pulse energy, THz-streaking [6, 7] for determination of the photon pulse time structure [8], as well as the online photoionisation spectrometer OPIS [9, 10] (see Fig. 1) and the so-called cookie-box [8, 11] which use photoelectron spectroscopy to get information about the spectral distribution of the FEL radiation. These diagnostic methods have the advantage that they can be designed to be almost completely non-invasive. In a photoionisation process, due to the high FEL intensity, a significant space charge [10] can be created in the ionised gas target in the interaction region of the instruments. This space charge even accumulates for high FEL pulse repetition rates, since the created target gas ions cannot dissipate fast enough by Coulomb repulsion or be replenished with fresh, unionised atoms before the next FEL pulse arrives. For instruments based on photoelectron

Journal of Instrumentation, 2009

Due to the stochastic nature of the Self Amplifying Spontaneous Emission (SASE) process and the r... more Due to the stochastic nature of the Self Amplifying Spontaneous Emission (SASE) process and the resulting pulse-to-pulse fluctuations of the Free Electron Laser (FEL) photon energies, experimenters working with FELs need to get real-time feedback about the photon properties for their experiments. Investigations of narrow atomic or molecular resonances, phase transitions, or any other kind of effect heavily dependent on photon energy would need to know the precise FEL photon energy for each individual photon bunch. Furthermore, any spectrometer developed to deliver the information of these properties should not significantly interfere or degrade the FEL beam. Therefore, the group at the Free Electron Laser in Hamburg (FLASH) has developed an online photoionization spectrometer that uses ion time of flight (I-TOF) measurement methods on noble gases to measure the photon energy of each pulse. This paper presents the first test results for the viability of this online photoionization spectrometer (OPS).

Journal of Synchrotron Radiation, 2019

X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse en... more X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. They are used for tuning and maintaining the self-amplified spontaneous emission (SASE) operation and for sorting single-shot experimental data according to the pulse-resolved energy monitor data. The XGMs were developed at DESY based on the specific requirements for the European XFEL. In total, six XGM units are continuously in operation. Here, the main principle and experimental setup of an XGM are summarized, and the locations of the six XGMs at the facility are shown. Pulse energy measurements at 0.134 nm wavelength are presented, exceeding 1 mJ obtained with an absolute measurement uncertainty of 7–10%; correlations between different XGMs are shown, from which a SASE1 beamline transmission of 97% is deduced. Additionally, simultaneous position measurements close to the undulator and at the end of the tunnel are shown, along wit...

FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for u... more FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable which allows to test and use advanced lasing concepts. In particular, we tested recently a two-color mode of operation based on the alternation of tunes of the undulator segments (every other segment is tuned to the second wavelength). This scheme is advantageous in comparison with a subsequent generation of two colors in two different parts of the undulator. First, source positions of two FEL beams are close to each other which makes it easier to handle them. Second, the amplification is more efficient in this configuration since the segments with respectively "wrong" wavelength act as bunchers. We developed methods for online intensity measurements of the two colors simultaneously that require a combination of two detectors. We present some examples of such measurements in the XUV and soft X...

Free-electron lasers deliver VUV and soft x-ray pulses with the highest brilliance available and ... more Free-electron lasers deliver VUV and soft x-ray pulses with the highest brilliance available and high spatial coherence. Users of such facilities have high demands on phase and coherence properties of the beam, for instance when working with coherent diffractive imaging (CDI). To gain highly resolved spatial coherence information, we have performed a caustic scan at BL2 of FLASH using the ellipsoidal beam line focusing mirror and a movable XUV sensitive CCD detector. This measurement allows for retrieving the Wigner distribution function, being the two-dimensional Fourier transform of the mutual intensity of the beam. Computing the reconstruction on a fourdimensional grid, this yields the Wigner distribution which describes the beam propagation completely. Hence, we are able to provide comprehensive information about spatial coherence properties of the FLASH beam including the mutual coherence function and the global degree of coherence. Additionally, we derive the beam propagation ...

The rapid development of a new generation of X-ray radiation sources providing ultrashort (from a... more The rapid development of a new generation of X-ray radiation sources providing ultrashort (from atto- to femtoseconds) pulses creates unique possibilities for generating high energy density states of matter. Instruments, like free-electron lasers (FELs) produce pulses of very high intensity and allow to extend the optical studies of radiation induced phase transitions of solids. The excitation of solid materials with x-ray femtosecond pulses offers a number of advantages over irradiation with femtosecond optical lasers. First of all the energy deposition process is not influenced by optical nonlinearities i.e. multiphoton absorption and free carrier absorption. Moreover the absorption depth can be varied over many orders of magnitude. E.g. for silicon it changes from a few nanometres up to hundreds of microns. Therefore, ultrashort X-ray pulses allow the preparation of well-defined excitation conditions in variable sample volumes and thus to study the energy transport processes. Single shot irradiations of the Si flat mirror were performed at SACLA FEL facilities in the range of 5.5 – 12 keV photon energies, at normal and grazing incidence angles. Observed radiation induced structural modification of materials is related to melting of silicon and its resolidification and a have threshold nature. The experimental damage thresholds are the highest in case of the irradiations below the critical angles. In these cases the energy density of the radiation absorbed at the sample’s surface can reach above a melting threshold (approx. 1eV/atom) without any structural modification. This may be explained by the transport of the energy out of the excitation volume (limited to the absorption skin depth) by hot electrons on the time scales shorter than the one typical for the electron-phonon coupling (~2 ps for Si). Modelling of the energy transport by ballistic electrons has been performed by means of the PENELOPE simulation code

Journal of Synchrotron Radiation, 2019

X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration.... more X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration. These sources are chaotic by nature and therefore, to be used at their full potential, require that every X-ray pulse is characterized in terms of various relevant properties such as intensity, photon energy, position and timing. Diagnostics are for example installed on an X-ray beamline to specifically monitor the intensity of individual X-ray pulses. To date, these can however only provide a single-shot value of the relative number of photons per shot. Here are reported measurements made in January 2015 of the absolute number of photons in the hard X-ray regime at LCLS which is typically 3.5 × 1011 photons shot−1 between 6 and 9.5 keV at the X-ray Pump–Probe instrument. Moreover, an average transmission of ≈62% of the hard X-ray beamline over this energy range is measured and the third-harmonic content of ≈0.47% below 9 keV is characterized.

With FLASH2020+, a major upgrade of the FLASH facility has started to meet the new requirements o... more With FLASH2020+, a major upgrade of the FLASH facility has started to meet the new requirements of the growing soft-x ray user community. The design of the FEL beamlines aims at photon properties suitable to the needs of future user experiments with high repetition rate XUV and soft X-ray radiation. By the end of the project, both existing FEL lines at FLASH will be equipped with fully tunable undulators capable of delivering photon pulses with variable polarization. The use of the external seeding at 1 MHz in burst mode is part of the design of the new FLASH1 beamline, while FLASH2 will exploit novel lasing concepts based on different undulator configurations. The new FLASH2020+ will rely on an electron beam energy of 1.35 GeV that will extend the accessible wavelength range to the oxygen K-edge with variable polarization. The facility will be completed with new laser sources for pump and probe experiment and new experimental stations.

In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) dete... more In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) detects scattered radiation from a target (mesh). Use of different targets and geometrical positioning of the MCP plates provides control of photon flux on the detector. MCP detector covers the whole wavelength range of FLASH2 (from 2.x nm to 100 nm). Dynamic range spans from sub-nJ to mJ level (from spontaneous to saturation level). Relative accuracy of single-shot radiation pulse energy measurements in the exponential gain regime is about 1%. DAQ based software is under development which allows to perform cross-correlation of the SASE FEL performance with electron beam jitters. As a result, it is possible: (i) to organize efficient feedback for cancellation of machine jitters, and (ii) to use statistical techniques for characterization of SASE FEL radiation deriving such important quantities as gain curve (gain of the radiation pulse energy and its fluctuations along the undulator), radiat...

X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation V

Photon beam diagnostics play an essential role for tun- ing free-electron lasers (FEL) and delive... more Photon beam diagnostics play an essential role for tun- ing free-electron lasers (FEL) and delivering the requested beam properties to the users. An overview of the FLASH1 and FLASH2 photon diagnostic devices will be presented with emphasis onthe newpulse resolvingintensitymonitor covering an extended energy range.

FLASH, the Free-electron LASer in Hamburg, is the world’s first free electron laser for extremely... more FLASH, the Free-electron LASer in Hamburg, is the world’s first free electron laser for extremely bright and ultra-short pulses in the extreme ultraviolet and soft X-ray range. Efficient photon beam transport and diagnostics play an essential role in exploiting the features of this new generation of light sources in a large variety of user experiments. A detailed overview of the FLASH user facility is presented.

Optics Express

Proper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important fo... more Proper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz (MHz) repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5-nm beam generated by the free-electron laser in Hamburg (FLASH) using the method of multi-pulse desorption imprints in poly(methyl methacrylate)(PMMA). The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single-shot ablation imprints and multi-shot desorption imprints at both low (10 Hz) and high (1 MHz) repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function model.

Journal of Synchrotron Radiation

Journal of Synchrotron Radiation, 2019

The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissF... more The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissFEL has been measured with an X-ray gas monitor from DESY and compared with a PSI gas detector upstream of the optical components. The transmission efficiencies of the Mo, Si and SiC mirror coatings of the Aramis beamline and the various other in-beam components were evaluated and compared with theoretical calculations, showing an agreement of 6% or better in all cases. The experiment has also shown the efficacy of the high-harmonic rejection mirrors at the Bernina branch of the Aramis beamline at SwissFEL, and characterized the transmission efficiency of the on-line spectrometer in the Aramis beamline. The theoretical transmission of the mirror coatings match the experimental data to within 7%. The accuracy of these measurements was checked against a radiative bolometer from a Japanese collaboration and found to agree to a level of 4% or better. Further comparisons with a diamond detecto...

Nature Photonics, 2020

In the version of this Article originally published, the surname of the author N. Johansson was m... more In the version of this Article originally published, the surname of the author N. Johansson was misspelled as 'Johannson'. In addition, in affiliation 17, "University of Łódź" was incorrect; it should have read "Łódź University of Technology". These errors have been corrected in the online versions of the Article and its Supplementary Information.

Cornell University - arXiv, Jun 23, 2022

We present real-world data processing on measured electron time-of-flight data via neural network... more We present real-world data processing on measured electron time-of-flight data via neural networks. Specifically, the use of disentangled variational autoencoders on data from a diagnostic instrument for online wavelength monitoring at the free electron laser FLASH in Hamburg. Without a-priori knowledge the network is able to find representations of single-shot FEL spectra, which have a low signal-to-noise ratio. This reveals, in a directly human-interpretable way, crucial information about the photon properties. The central photon energy and the intensity as well as very detector-specific features are identified. The network is also capable of data cleaning, i.e. denoising, as well as the removal of artefacts. In the reconstruction, this allows for identification of signatures with very low intensity which are hardly recognisable in the raw data. In this particular case, the network enhances the quality of the diagnostic analysis at FLASH. However, this unsupervised method also has the potential to improve the analysis of other similar types of spectroscopy data. Motivation SASE-FEL challenge Free electron lasers (FEL) enable atomic and molecular science in the femtosecond to attosecond regime by creating highly intense photon pulses on that time scale. However, FELs which are based on the principle of self-amplified spontaneous emission (SASE) [1, 2], such as FLASH [3], produce spatial, spectral and temporal pulse properties that are strongly fluctuating from pulse to pulse. Hence, a reliable photon diagnostic on a single-shot basis is essential for sound data analysis of scientific user experiments performed at such facilities. Post-experiment sorting of recorded data with respect to different properties, such as intensity or wavelength, can reveal signatures of physical processes otherwise obscured or even hidden in the data sets. A number of diagnostic instruments at FELs are used to measure the photoionisation of gas targets, such as the Gas Monitor Detector (GMD) [4, 5] for measurement of absolute pulse energy, THz-streaking [6, 7] for determination of the photon pulse time structure [8], as well as the online photoionisation spectrometer OPIS [9, 10] (see Fig. 1) and the so-called cookie-box [8, 11] which use photoelectron spectroscopy to get information about the spectral distribution of the FEL radiation. These diagnostic methods have the advantage that they can be designed to be almost completely non-invasive. In a photoionisation process, due to the high FEL intensity, a significant space charge [10] can be created in the ionised gas target in the interaction region of the instruments. This space charge even accumulates for high FEL pulse repetition rates, since the created target gas ions cannot dissipate fast enough by Coulomb repulsion or be replenished with fresh, unionised atoms before the next FEL pulse arrives. For instruments based on photoelectron

Journal of Instrumentation, 2009

Due to the stochastic nature of the Self Amplifying Spontaneous Emission (SASE) process and the r... more Due to the stochastic nature of the Self Amplifying Spontaneous Emission (SASE) process and the resulting pulse-to-pulse fluctuations of the Free Electron Laser (FEL) photon energies, experimenters working with FELs need to get real-time feedback about the photon properties for their experiments. Investigations of narrow atomic or molecular resonances, phase transitions, or any other kind of effect heavily dependent on photon energy would need to know the precise FEL photon energy for each individual photon bunch. Furthermore, any spectrometer developed to deliver the information of these properties should not significantly interfere or degrade the FEL beam. Therefore, the group at the Free Electron Laser in Hamburg (FLASH) has developed an online photoionization spectrometer that uses ion time of flight (I-TOF) measurement methods on noble gases to measure the photon energy of each pulse. This paper presents the first test results for the viability of this online photoionization spectrometer (OPS).

Journal of Synchrotron Radiation, 2019

X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse en... more X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. They are used for tuning and maintaining the self-amplified spontaneous emission (SASE) operation and for sorting single-shot experimental data according to the pulse-resolved energy monitor data. The XGMs were developed at DESY based on the specific requirements for the European XFEL. In total, six XGM units are continuously in operation. Here, the main principle and experimental setup of an XGM are summarized, and the locations of the six XGMs at the facility are shown. Pulse energy measurements at 0.134 nm wavelength are presented, exceeding 1 mJ obtained with an absolute measurement uncertainty of 7–10%; correlations between different XGMs are shown, from which a SASE1 beamline transmission of 97% is deduced. Additionally, simultaneous position measurements close to the undulator and at the end of the tunnel are shown, along wit...

FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for u... more FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable which allows to test and use advanced lasing concepts. In particular, we tested recently a two-color mode of operation based on the alternation of tunes of the undulator segments (every other segment is tuned to the second wavelength). This scheme is advantageous in comparison with a subsequent generation of two colors in two different parts of the undulator. First, source positions of two FEL beams are close to each other which makes it easier to handle them. Second, the amplification is more efficient in this configuration since the segments with respectively "wrong" wavelength act as bunchers. We developed methods for online intensity measurements of the two colors simultaneously that require a combination of two detectors. We present some examples of such measurements in the XUV and soft X...

Free-electron lasers deliver VUV and soft x-ray pulses with the highest brilliance available and ... more Free-electron lasers deliver VUV and soft x-ray pulses with the highest brilliance available and high spatial coherence. Users of such facilities have high demands on phase and coherence properties of the beam, for instance when working with coherent diffractive imaging (CDI). To gain highly resolved spatial coherence information, we have performed a caustic scan at BL2 of FLASH using the ellipsoidal beam line focusing mirror and a movable XUV sensitive CCD detector. This measurement allows for retrieving the Wigner distribution function, being the two-dimensional Fourier transform of the mutual intensity of the beam. Computing the reconstruction on a fourdimensional grid, this yields the Wigner distribution which describes the beam propagation completely. Hence, we are able to provide comprehensive information about spatial coherence properties of the FLASH beam including the mutual coherence function and the global degree of coherence. Additionally, we derive the beam propagation ...

The rapid development of a new generation of X-ray radiation sources providing ultrashort (from a... more The rapid development of a new generation of X-ray radiation sources providing ultrashort (from atto- to femtoseconds) pulses creates unique possibilities for generating high energy density states of matter. Instruments, like free-electron lasers (FELs) produce pulses of very high intensity and allow to extend the optical studies of radiation induced phase transitions of solids. The excitation of solid materials with x-ray femtosecond pulses offers a number of advantages over irradiation with femtosecond optical lasers. First of all the energy deposition process is not influenced by optical nonlinearities i.e. multiphoton absorption and free carrier absorption. Moreover the absorption depth can be varied over many orders of magnitude. E.g. for silicon it changes from a few nanometres up to hundreds of microns. Therefore, ultrashort X-ray pulses allow the preparation of well-defined excitation conditions in variable sample volumes and thus to study the energy transport processes. Single shot irradiations of the Si flat mirror were performed at SACLA FEL facilities in the range of 5.5 – 12 keV photon energies, at normal and grazing incidence angles. Observed radiation induced structural modification of materials is related to melting of silicon and its resolidification and a have threshold nature. The experimental damage thresholds are the highest in case of the irradiations below the critical angles. In these cases the energy density of the radiation absorbed at the sample’s surface can reach above a melting threshold (approx. 1eV/atom) without any structural modification. This may be explained by the transport of the energy out of the excitation volume (limited to the absorption skin depth) by hot electrons on the time scales shorter than the one typical for the electron-phonon coupling (~2 ps for Si). Modelling of the energy transport by ballistic electrons has been performed by means of the PENELOPE simulation code

Journal of Synchrotron Radiation, 2019

X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration.... more X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration. These sources are chaotic by nature and therefore, to be used at their full potential, require that every X-ray pulse is characterized in terms of various relevant properties such as intensity, photon energy, position and timing. Diagnostics are for example installed on an X-ray beamline to specifically monitor the intensity of individual X-ray pulses. To date, these can however only provide a single-shot value of the relative number of photons per shot. Here are reported measurements made in January 2015 of the absolute number of photons in the hard X-ray regime at LCLS which is typically 3.5 × 1011 photons shot−1 between 6 and 9.5 keV at the X-ray Pump–Probe instrument. Moreover, an average transmission of ≈62% of the hard X-ray beamline over this energy range is measured and the third-harmonic content of ≈0.47% below 9 keV is characterized.

With FLASH2020+, a major upgrade of the FLASH facility has started to meet the new requirements o... more With FLASH2020+, a major upgrade of the FLASH facility has started to meet the new requirements of the growing soft-x ray user community. The design of the FEL beamlines aims at photon properties suitable to the needs of future user experiments with high repetition rate XUV and soft X-ray radiation. By the end of the project, both existing FEL lines at FLASH will be equipped with fully tunable undulators capable of delivering photon pulses with variable polarization. The use of the external seeding at 1 MHz in burst mode is part of the design of the new FLASH1 beamline, while FLASH2 will exploit novel lasing concepts based on different undulator configurations. The new FLASH2020+ will rely on an electron beam energy of 1.35 GeV that will extend the accessible wavelength range to the oxygen K-edge with variable polarization. The facility will be completed with new laser sources for pump and probe experiment and new experimental stations.

In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) dete... more In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) detects scattered radiation from a target (mesh). Use of different targets and geometrical positioning of the MCP plates provides control of photon flux on the detector. MCP detector covers the whole wavelength range of FLASH2 (from 2.x nm to 100 nm). Dynamic range spans from sub-nJ to mJ level (from spontaneous to saturation level). Relative accuracy of single-shot radiation pulse energy measurements in the exponential gain regime is about 1%. DAQ based software is under development which allows to perform cross-correlation of the SASE FEL performance with electron beam jitters. As a result, it is possible: (i) to organize efficient feedback for cancellation of machine jitters, and (ii) to use statistical techniques for characterization of SASE FEL radiation deriving such important quantities as gain curve (gain of the radiation pulse energy and its fluctuations along the undulator), radiat...

X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation V

Photon beam diagnostics play an essential role for tun- ing free-electron lasers (FEL) and delive... more Photon beam diagnostics play an essential role for tun- ing free-electron lasers (FEL) and delivering the requested beam properties to the users. An overview of the FLASH1 and FLASH2 photon diagnostic devices will be presented with emphasis onthe newpulse resolvingintensitymonitor covering an extended energy range.

FLASH, the Free-electron LASer in Hamburg, is the world’s first free electron laser for extremely... more FLASH, the Free-electron LASer in Hamburg, is the world’s first free electron laser for extremely bright and ultra-short pulses in the extreme ultraviolet and soft X-ray range. Efficient photon beam transport and diagnostics play an essential role in exploiting the features of this new generation of light sources in a large variety of user experiments. A detailed overview of the FLASH user facility is presented.

Optics Express

Proper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important fo... more Proper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz (MHz) repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5-nm beam generated by the free-electron laser in Hamburg (FLASH) using the method of multi-pulse desorption imprints in poly(methyl methacrylate)(PMMA). The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single-shot ablation imprints and multi-shot desorption imprints at both low (10 Hz) and high (1 MHz) repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function model.

Journal of Synchrotron Radiation