FEL2012 - List of Authors (Yurkov, M.V.)

Paper

Title

Page

Harmonic Lasing in X-ray FELs

45

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

Contrary to nonlinear harmonic generation, harmonic lasing in a high-gain FEL can provide much more intense, stable,and narrow-band FEL beam which is easier to handle if the fundamental is suppressed. We propose efficient methods for suppression of the fundamental. We perform a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics, and present explicit expression for FEL gain length, taking into account all essential effects. We conclude that harmonic lasing is much more robust than usually thought, and can be widely used in the existing or planned X-ray FEL facilities. LCLS after a minor modification can lase at the 3rd harmonic up to the photon energy of 25-30 keV providing multi-gigawatt power level. At the European XFEL the harmonic lasing would allow to extend operating range (ultimately up to 100 keV), to increase brilliance, to enable two-color operation for pump-probe experiments,and to provide more flexible operation at different electron energies. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities, harmonics can grow faster than the fundamental.

MOPD04

Fitting Formulas for Harmonic Lasing in FEL Amplifiers

49

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

One of the most important subjects of the high-gain FEL engineering is the calculation of the gain length, and fitting formulas are frequently used for this purpose. Here we refer to Ming Xie fitting formulas [1] and fitting formulas for optimized FEL written down in an explicit form in terms of the electron beam and undulator parameters [2]. In this paper we perform generalization of these fitting formulas to the case of harmonic lasing.
[1] M. Xie, Nucl. Instrum. and Methods A445(2000)59
[2] E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov,
Opt. Commun. 235(2004)415

MOPD05

Harmonic Lasing of Thin Electron Beam

53

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

For a typical operating range of hard X-ray FELs the condition 2π ε/λ ~ 1 is usually a design goal for the shortest wavelength. In the case of the simultaneous lasing the fundamental mode has shorter gain length than harmonics. If the same electron beam is used to drive an FEL in a soft X-ray beamline, the regime with 2π ε/λ << 1 is realized which corresponds to the case of a small value of diffraction parameter. Here we present a detailed study of this regime. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities (like SASE3 beamline of the European XFEL), harmonics can grow faster than the fundamental wavelength. This feature can be used in some experiments, but might also be an unwanted phenomenon, and we discuss possible measures to diminish it.

MOPD06

Spatial Properties of the Radiation from SASE FELs at the European XFEL

57

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

Recently DESY and the European XFEL GmbH performed revision of the baseline parameters for the electron beam. Operating range of bunch charges has been extended from 20 pC to 1 nC. Different modes of FEL operation become possible with essentially different properties of the radiation. Radiation from SASE FEL with planar undulator contains visible contribution of higher odd harmonics. Knowledge of spatial properties of harmonics is of great practical interest for planning user experiments. In this report we present results of the studies of spatial properties of the radiation from SASE FELs at the European XFEL. We consider nonlinear mechanism of harmonic generation and trace spatial properties of the odd harmonics up to deep nonlinear regime.

MOPD07

On Disruption of the Fundamental Harmonic in SASE FEL with Phase Shifters

61

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

A method to disrupt the fundamental harmonic with phase shifters installed between undulator modules (while keeping the lasing at the third harmonic undisturbed) was proposed in [*]. If phase shifters are tuned such that the phase delay is 2π/3 (or 4π/3) for the fundamental, then its amplification is disrupted. At the same time the phase shift is equal to 2π for the third harmonic, i.e. it continues to get amplified without being affected by phase shifters. We note that simulations in [*] were done for the case of a monochromatic seed, and the results cannot be applied for a SASE FEL. The reason is that in the latter case the amplified frequencies are defined self-consistently, i.e. there is frequency shift (red or blue) depending on positions and magnitudes of phase kicks. This leads to a significantly weaker suppression effect. In particular, we found out that a consecutive use of phase shifters with the same phase kicks 2π/3 (as proposed in [*] is inefficient, i.e. it does not lead to a sufficiently strong suppression of the fundamental wavelength. In the present report we propose a modification of phase shifters method that can work in the case of a SASE FEL.
[*] B.W.J. McNeil et al., Phy. Rev. Lett. 96, 084801 (2006).

MOPD08

Coherence Properties of the Odd Harmonics of the Radiation from SASE FEL with Planar Undulator

65

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

We present a comprehensive analysis of coherence properties of odd harmonics radiated from a SASE FEL with planar undulator. Nonlinear mechanism of harmonic generation is under study. Temporal and space correlation functions, coherence time and degree of transverse coherence are calculated by means of numerical simulations with the code FAST. Similarity techniques have been used to derive general coherence properties of the radiation in the saturation regime.

WEPD55

Tunable IR/THz Source for Pump Probe Experiments at the European XFEL

503

M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We present a concept of an accelerator based source of powerful, coherent THz radiation for pump-probe experiments at the European XFEL. The electron accelerator is similar to that operating at the PITZ facility. It consists of rf gun and warm accelerating section (energy up to 30 MeV). The radiation is generated in a 5 meter long APPLE-type undulator with a period length of 4 cm, thus providing polarization control. Radiation with wavelength below 200 micrometers is generated using the mechanism of SASE FEL. Powerful coherent radiation with wavelength above 200 micrometers is generated in the undulator by a tailored (compressed) electron beam. Properties of the radiation are: wavelength range is 10 to 1000 micrometers (30 THz - 0.3 THz), radiation pulse energy is up to a few hundreds microjoles, peak power is 10 to 100 MW, spectrum bandwidth is 2 - 3%. It is important to note that the time structure of the THZ source ideally matches with the time structure of the x-ray pulses since the THZ source is based on the same technology as the injector of the European XFEL. A similar scheme can be also realized at LCLS, SACLA, or SWISS FEL with S-band rf accelerator technology.

THOC02

Determination of Temporal FEL Pulse Properties: Challenging Concepts and Experiments

N. Stojanovic, S. Düsterer, B. Schmidt, E. Schneidmiller, S. Schreiber, M.V. Yurkov
DESY, Hamburg, Germany
M. Drescher, W. Wurth
Uni HH, Hamburg, Germany
R. Mitzner
HZB, Berlin, Germany

Funding: BMBF, 05K10CHC
One of the most challenging tasks for the FEL photon diagnostics is the determination of the pulse duration - even more so information on the temporal substructure. The knowledge of the temporal pulse characteristics is important for wide range of experiments, from interaction of materials with high intensity radiation to ultrafast pump-probe studies. Here, the temporal resolution depends on the pulse duration as well as on the precise arrival time between the pump and probe pulse. Due to the wide range of available parameters at the existing and planned FELs, the photon energies are ranging from VUV to X-rays and pulse durations from sub fs up to 1ps range. Thus, a variety of methods has to be considered in order to characterize its temporal structure. Moreover due to the statistical nature of the SASE process, the pulse shape (consisting of multitude of sub-pulses) varies from shot to shot. Ultimately, single-shot pulse characterization is needed, which by far increases the level of complexity comparing to averaging techniques utilized so far. Here we present an overview of the different pulse diagnostics techniques that were utilized at FLASH in Hamburg.

Paper	Title	Page
MOPD03	Harmonic Lasing in X-ray FELs	45
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Contrary to nonlinear harmonic generation, harmonic lasing in a high-gain FEL can provide much more intense, stable,and narrow-band FEL beam which is easier to handle if the fundamental is suppressed. We propose efficient methods for suppression of the fundamental. We perform a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics, and present explicit expression for FEL gain length, taking into account all essential effects. We conclude that harmonic lasing is much more robust than usually thought, and can be widely used in the existing or planned X-ray FEL facilities. LCLS after a minor modification can lase at the 3rd harmonic up to the photon energy of 25-30 keV providing multi-gigawatt power level. At the European XFEL the harmonic lasing would allow to extend operating range (ultimately up to 100 keV), to increase brilliance, to enable two-color operation for pump-probe experiments,and to provide more flexible operation at different electron energies. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities, harmonics can grow faster than the fundamental.

MOPD04	Fitting Formulas for Harmonic Lasing in FEL Amplifiers	49
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	One of the most important subjects of the high-gain FEL engineering is the calculation of the gain length, and fitting formulas are frequently used for this purpose. Here we refer to Ming Xie fitting formulas [1] and fitting formulas for optimized FEL written down in an explicit form in terms of the electron beam and undulator parameters [2]. In this paper we perform generalization of these fitting formulas to the case of harmonic lasing. [1] M. Xie, Nucl. Instrum. and Methods A445(2000)59 [2] E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov, Opt. Commun. 235(2004)415

MOPD05	Harmonic Lasing of Thin Electron Beam	53
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	For a typical operating range of hard X-ray FELs the condition 2π ε/λ ~ 1 is usually a design goal for the shortest wavelength. In the case of the simultaneous lasing the fundamental mode has shorter gain length than harmonics. If the same electron beam is used to drive an FEL in a soft X-ray beamline, the regime with 2π ε/λ << 1 is realized which corresponds to the case of a small value of diffraction parameter. Here we present a detailed study of this regime. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities (like SASE3 beamline of the European XFEL), harmonics can grow faster than the fundamental wavelength. This feature can be used in some experiments, but might also be an unwanted phenomenon, and we discuss possible measures to diminish it.

MOPD06	Spatial Properties of the Radiation from SASE FELs at the European XFEL	57
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Recently DESY and the European XFEL GmbH performed revision of the baseline parameters for the electron beam. Operating range of bunch charges has been extended from 20 pC to 1 nC. Different modes of FEL operation become possible with essentially different properties of the radiation. Radiation from SASE FEL with planar undulator contains visible contribution of higher odd harmonics. Knowledge of spatial properties of harmonics is of great practical interest for planning user experiments. In this report we present results of the studies of spatial properties of the radiation from SASE FELs at the European XFEL. We consider nonlinear mechanism of harmonic generation and trace spatial properties of the odd harmonics up to deep nonlinear regime.

MOPD07	On Disruption of the Fundamental Harmonic in SASE FEL with Phase Shifters	61
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	A method to disrupt the fundamental harmonic with phase shifters installed between undulator modules (while keeping the lasing at the third harmonic undisturbed) was proposed in []. If phase shifters are tuned such that the phase delay is 2π/3 (or 4π/3) for the fundamental, then its amplification is disrupted. At the same time the phase shift is equal to 2π for the third harmonic, i.e. it continues to get amplified without being affected by phase shifters. We note that simulations in [] were done for the case of a monochromatic seed, and the results cannot be applied for a SASE FEL. The reason is that in the latter case the amplified frequencies are defined self-consistently, i.e. there is frequency shift (red or blue) depending on positions and magnitudes of phase kicks. This leads to a significantly weaker suppression effect. In particular, we found out that a consecutive use of phase shifters with the same phase kicks 2π/3 (as proposed in [] is inefficient, i.e. it does not lead to a sufficiently strong suppression of the fundamental wavelength. In the present report we propose a modification of phase shifters method that can work in the case of a SASE FEL. [] B.W.J. McNeil et al., Phy. Rev. Lett. 96, 084801 (2006).

MOPD08	Coherence Properties of the Odd Harmonics of the Radiation from SASE FEL with Planar Undulator	65
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We present a comprehensive analysis of coherence properties of odd harmonics radiated from a SASE FEL with planar undulator. Nonlinear mechanism of harmonic generation is under study. Temporal and space correlation functions, coherence time and degree of transverse coherence are calculated by means of numerical simulations with the code FAST. Similarity techniques have been used to derive general coherence properties of the radiation in the saturation regime.

WEPD55	Tunable IR/THz Source for Pump Probe Experiments at the European XFEL	503
	M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We present a concept of an accelerator based source of powerful, coherent THz radiation for pump-probe experiments at the European XFEL. The electron accelerator is similar to that operating at the PITZ facility. It consists of rf gun and warm accelerating section (energy up to 30 MeV). The radiation is generated in a 5 meter long APPLE-type undulator with a period length of 4 cm, thus providing polarization control. Radiation with wavelength below 200 micrometers is generated using the mechanism of SASE FEL. Powerful coherent radiation with wavelength above 200 micrometers is generated in the undulator by a tailored (compressed) electron beam. Properties of the radiation are: wavelength range is 10 to 1000 micrometers (30 THz - 0.3 THz), radiation pulse energy is up to a few hundreds microjoles, peak power is 10 to 100 MW, spectrum bandwidth is 2 - 3%. It is important to note that the time structure of the THZ source ideally matches with the time structure of the x-ray pulses since the THZ source is based on the same technology as the injector of the European XFEL. A similar scheme can be also realized at LCLS, SACLA, or SWISS FEL with S-band rf accelerator technology.

THOC02	Determination of Temporal FEL Pulse Properties: Challenging Concepts and Experiments
	N. Stojanovic, S. Düsterer, B. Schmidt, E. Schneidmiller, S. Schreiber, M.V. Yurkov DESY, Hamburg, Germany M. Drescher, W. Wurth Uni HH, Hamburg, Germany R. Mitzner HZB, Berlin, Germany
	Funding: BMBF, 05K10CHC One of the most challenging tasks for the FEL photon diagnostics is the determination of the pulse duration - even more so information on the temporal substructure. The knowledge of the temporal pulse characteristics is important for wide range of experiments, from interaction of materials with high intensity radiation to ultrafast pump-probe studies. Here, the temporal resolution depends on the pulse duration as well as on the precise arrival time between the pump and probe pulse. Due to the wide range of available parameters at the existing and planned FELs, the photon energies are ranging from VUV to X-rays and pulse durations from sub fs up to 1ps range. Thus, a variety of methods has to be considered in order to characterize its temporal structure. Moreover due to the statistical nature of the SASE process, the pulse shape (consisting of multitude of sub-pulses) varies from shot to shot. Ultimately, single-shot pulse characterization is needed, which by far increases the level of complexity comparing to averaging techniques utilized so far. Here we present an overview of the different pulse diagnostics techniques that were utilized at FLASH in Hamburg.