FEL2017 - List of Authors (Schneidmiller, E.)

Paper	Title	Page
MOBA01	Energy Chirp and Undulator Taper in FELs
	E. Schneidmiller DESY, Hamburg, Germany
	The effects of energy chirp and undulator taper in FELs and applications of these effects in different schemes are discussed. This includes an operation of FEL oscillators with reverse-tapered undulators; energy chirp effects in high-gain, short wavelength FELs like FLASH; compensation of the energy chirp by the undulator taper in high-gain FELs and the application of this effect for generation of attosecond X-ray pulses; reverse taper in high-gain FELs for circular polarization production and for an efficient, background-free harmonic generation. Some new ideas are briefly described such as strongly chirped X-ray pulses, an enhanced X-ray pulse compression, few-cycle hard X-ray pulses etc.
	Slides MOBA01 [1.303 MB]
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MOBA02	Coherence Limits of X-ray FEL Radiation	5
	M.V. Yurkov, E. Schneidmiller DESY, Hamburg, Germany
	The most simple and robust technique for production of short wavelength radiation is Self Amplified Spontaneous Emission (SASE) FEL. Amplification process in SASE FELs develops from the shot noise in the electron beam, and powerful radiation is produced by single pass of the electron beam through the undulator. Serving as a seed, shot noise effects impose fundamental limits on the coherence properties of the radiation (both, temporal and spatial). FEL theory reached mature status allowing elegant description of the shot noise phenomena, and in this report we present relevant overview.
	Slides MOBA02 [2.606 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOBA02
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MOP031	First Operation of a Harmonic Lasing Self-Seeded FEL	102
	E. Schneidmiller, B. Faatz, M. Kuhlmann, J. Rönsch-Schulenburg, S. Schreiber, M. Tischer, M.V. Yurkov DESY, Hamburg, Germany
	Harmonic lasing is a perspective mode of operation of X-ray FEL user facilities that allows it to provide brilliant beams of higher-energy photons for user experiments. Another useful application of harmonic lasing is so called Harmonic Lasing Self-Seeded Free Electron Laser (HLSS FEL), that allows it to improve spectral brightness of these facilities. In the past, harmonic lasing has been demonstrated in the FEL oscillators in infrared and visible wavelength ranges, but not in high-gain FELs and not at short wavelengths. In this paper, we report on the first evidence of the harmonic lasing and the first operation of the HLSS FEL at the soft X-ray FEL user facility FLASH in the wavelength range between 4.5 nm and 15 nm. Spectral brightness was improved in comparison with Self-Amplified Spontaneous emission (SASE) FEL by a factor of six in the exponential gain regime. A better performance of HLSS FEL with respect to SASE FEL in the post-saturation regime with a tapered undulator was observed as well. The first demonstration of harmonic lasing in a high-gain FEL and at a short wavelength paves the way for a variety of applications of this new operation mode in X-ray FELs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP031
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MOP032	Reverse Undulator Tapering for Polarization Control and Background-Free Harmonic Production in XFELs: Results from FLASH	106
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade, one can consider an installation of a short helical afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. There is an efficient method for such a suppression: an application of the reverse taper in the main undulator.* In this contribution, we present the results of experiments with reverse taper at FLASH2 where a high contrast between FEL intensities from the afterburner and from the reverse-tapered main undulator was demonstrated. Another important application of the reverse taper is a possibility to produce FEL harmonics in the afterburner (or in the last part of baseline gap-tunable undulator). We present recent results from FLASH2 where the second and the third harmonics were efficiently generated with a low background at the fundamental. * E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13-080702 (2013).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP032
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MOP033	Baseline Parameters of the European XFEL	109
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We present the latest update of the baseline parameters of the European XFEL. It is planned that the electron linac will operate at four fixed electron energies of 8.5, 12, 14, and 17.5 GeV. Tunable gap undulators provide the possibility to change the radiation wavelength in a wide range. Operation with different bunch charges (0.02, 0.1, 0.25, 0.5 and 1 nC) provides the possibility to operate XFEL with different radiation pulse duration. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP033
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MOP035	Optimum Undulator Tapering of SASE FEL: Theory and Experimental Results From FLASH2	113
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Optimization of the amplification process in FEL amplifier with diffraction effects taken into account results in a specific law of the undulator tapering.* It is a smooth function with quadratic behavior in the beginning of the tapering section which transforms to a linear behavior for a long undulator. In practice, an undulator consists of a sequence of modules of fixed length separated with intersections. Two modes of undulator tapering can be implemented: step tapering and smooth tapering. Step tapering uses a step change of the undulator gap from module to module, while smooth tapering assumes additional linear change of the gap along each module. In this report, we simulate the performance of both experimental options and compare with theoretical limit. * E.A. Schneidmiller and M.V. Yurkov, Optimization of a high efficiency free electron laser amplifier, Phys. Rev. ST Accel. Beams 18-030705 (2015).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP035
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MOP036	Frequency Doubling Mode of Operation of Free Electron Laser FLASH2	117
	M. Kuhlmann, E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We report on the results of the first operation of a frequency doubler at free electron laser FLASH2. The scheme uses the feature of the variable-gap undulator. The undulator is divided into two parts. The second part of the undulator is tuned to the double frequency of the first part. The amplification process in the first undulator part is stopped at the onset of the nonlinear regime, such that nonlinear higher-harmonic bunching in the electron beam density becomes pronouncing, but the radiation level is still small to disturb the electron beam significantly. The modulated electron beam enters the second part of the undulator and generates radiation at the second harmonic. A frequency doubler allows operation in a two-color mode and operation at shorter wavelengths with respect to standard SASE scheme. Tuning of the electron beam trajectory, phase shifters and compression allows tuning of intensities of the first and the second harmonic. The shortest wavelength of 3.1 nm (photon energy 400 eV) has been achieved with a frequency doubler scheme, which is significantly below the design value for the standard SASE option.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP036
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TUA01	Recent FEL Experiments at FLASH	210
	S. Schreiber, E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	The FLASH free-electron laser user facility at DESY (Hamburg, Germany) provides high brilliance SASE FEL radiation in the XUV and soft X-ray wavelength range. With the recent installation of a second undulator beamline (FLASH2), variable-gap undulators are now available. They now allow various experiments not possible with the FLASH1 fixed gap undulators. We report on experiments on tapering, harmonic lasing, reverse tapering, frequency doubling at FLASH2 and experiments using double pulses for specific SASE and THz experiments at FLASH1.
	Slides TUA01 [4.124 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUA01
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

MOBA01

Energy Chirp and Undulator Taper in FELs

E. Schneidmiller
DESY, Hamburg, Germany

The effects of energy chirp and undulator taper in FELs and applications of these effects in different schemes are discussed. This includes an operation of FEL oscillators with reverse-tapered undulators; energy chirp effects in high-gain, short wavelength FELs like FLASH; compensation of the energy chirp by the undulator taper in high-gain FELs and the application of this effect for generation of attosecond X-ray pulses; reverse taper in high-gain FELs for circular polarization production and for an efficient, background-free harmonic generation. Some new ideas are briefly described such as strongly chirped X-ray pulses, an enhanced X-ray pulse compression, few-cycle hard X-ray pulses etc.

Slides MOBA01 [1.303 MB]

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOBA02

Coherence Limits of X-ray FEL Radiation

5

M.V. Yurkov, E. Schneidmiller
DESY, Hamburg, Germany

The most simple and robust technique for production of short wavelength radiation is Self Amplified Spontaneous Emission (SASE) FEL. Amplification process in SASE FELs develops from the shot noise in the electron beam, and powerful radiation is produced by single pass of the electron beam through the undulator. Serving as a seed, shot noise effects impose fundamental limits on the coherence properties of the radiation (both, temporal and spatial). FEL theory reached mature status allowing elegant description of the shot noise phenomena, and in this report we present relevant overview.

Slides MOBA02 [2.606 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOBA02

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOP031

First Operation of a Harmonic Lasing Self-Seeded FEL

102

E. Schneidmiller, B. Faatz, M. Kuhlmann, J. Rönsch-Schulenburg, S. Schreiber, M. Tischer, M.V. Yurkov
DESY, Hamburg, Germany

Harmonic lasing is a perspective mode of operation of X-ray FEL user facilities that allows it to provide brilliant beams of higher-energy photons for user experiments. Another useful application of harmonic lasing is so called Harmonic Lasing Self-Seeded Free Electron Laser (HLSS FEL), that allows it to improve spectral brightness of these facilities. In the past, harmonic lasing has been demonstrated in the FEL oscillators in infrared and visible wavelength ranges, but not in high-gain FELs and not at short wavelengths. In this paper, we report on the first evidence of the harmonic lasing and the first operation of the HLSS FEL at the soft X-ray FEL user facility FLASH in the wavelength range between 4.5 nm and 15 nm. Spectral brightness was improved in comparison with Self-Amplified Spontaneous emission (SASE) FEL by a factor of six in the exponential gain regime. A better performance of HLSS FEL with respect to SASE FEL in the post-saturation regime with a tapered undulator was observed as well. The first demonstration of harmonic lasing in a high-gain FEL and at a short wavelength paves the way for a variety of applications of this new operation mode in X-ray FELs.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP031

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOP032

Reverse Undulator Tapering for Polarization Control and Background-Free Harmonic Production in XFELs: Results from FLASH

106

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade, one can consider an installation of a short helical afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. There is an efficient method for such a suppression: an application of the reverse taper in the main undulator.* In this contribution, we present the results of experiments with reverse taper at FLASH2 where a high contrast between FEL intensities from the afterburner and from the reverse-tapered main undulator was demonstrated. Another important application of the reverse taper is a possibility to produce FEL harmonics in the afterburner (or in the last part of baseline gap-tunable undulator). We present recent results from FLASH2 where the second and the third harmonics were efficiently generated with a low background at the fundamental.
* E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13-080702 (2013).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP032

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOP033

Baseline Parameters of the European XFEL

109

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We present the latest update of the baseline parameters of the European XFEL. It is planned that the electron linac will operate at four fixed electron energies of 8.5, 12, 14, and 17.5 GeV. Tunable gap undulators provide the possibility to change the radiation wavelength in a wide range. Operation with different bunch charges (0.02, 0.1, 0.25, 0.5 and 1 nC) provides the possibility to operate XFEL with different radiation pulse duration. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP033

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOP035

Optimum Undulator Tapering of SASE FEL: Theory and Experimental Results From FLASH2

113

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Optimization of the amplification process in FEL amplifier with diffraction effects taken into account results in a specific law of the undulator tapering.* It is a smooth function with quadratic behavior in the beginning of the tapering section which transforms to a linear behavior for a long undulator. In practice, an undulator consists of a sequence of modules of fixed length separated with intersections. Two modes of undulator tapering can be implemented: step tapering and smooth tapering. Step tapering uses a step change of the undulator gap from module to module, while smooth tapering assumes additional linear change of the gap along each module. In this report, we simulate the performance of both experimental options and compare with theoretical limit.
* E.A. Schneidmiller and M.V. Yurkov, Optimization of a high efficiency free electron laser amplifier, Phys. Rev. ST Accel. Beams 18-030705 (2015).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP035

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOP036

Frequency Doubling Mode of Operation of Free Electron Laser FLASH2

117

M. Kuhlmann, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We report on the results of the first operation of a frequency doubler at free electron laser FLASH2. The scheme uses the feature of the variable-gap undulator. The undulator is divided into two parts. The second part of the undulator is tuned to the double frequency of the first part. The amplification process in the first undulator part is stopped at the onset of the nonlinear regime, such that nonlinear higher-harmonic bunching in the electron beam density becomes pronouncing, but the radiation level is still small to disturb the electron beam significantly. The modulated electron beam enters the second part of the undulator and generates radiation at the second harmonic. A frequency doubler allows operation in a two-color mode and operation at shorter wavelengths with respect to standard SASE scheme. Tuning of the electron beam trajectory, phase shifters and compression allows tuning of intensities of the first and the second harmonic. The shortest wavelength of 3.1 nm (photon energy 400 eV) has been achieved with a frequency doubler scheme, which is significantly below the design value for the standard SASE option.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP036

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUA01

Recent FEL Experiments at FLASH

210

S. Schreiber, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

The FLASH free-electron laser user facility at DESY (Hamburg, Germany) provides high brilliance SASE FEL radiation in the XUV and soft X-ray wavelength range. With the recent installation of a second undulator beamline (FLASH2), variable-gap undulators are now available. They now allow various experiments not possible with the FLASH1 fixed gap undulators. We report on experiments on tapering, harmonic lasing, reverse tapering, frequency doubling at FLASH2 and experiments using double pulses for specific SASE and THz experiments at FLASH1.

Slides TUA01 [4.124 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUA01

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)