FEL2014 - List of Authors (Lechner, C.)

Paper

Title

Page

Demonstration of SASE Suppression Through a Seeded Microbunching Instability

177

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov
DESY, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355.
Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP089

Overview of FEL Seeding Activities at FLASH

J. Bödewadt, S. Ackermann, R.W. Aßmann, N. Ekanayake, B. Faatz, G. Feng, I. Hartl, R. Ivanov, T. Laarmann, J.M. Mueller, T. Tanikawa
DESY, Hamburg, Germany
S. Ackermann, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Roßbach
Uni HH, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

The free-electron laser facility FLASH at DESY operates since several years in SASE mode, delivering high-intensity FEL pulses in the extreme ultra violet and soft x-ray wavelength range for users. In order to get more control of the characteristics of the FEL pulses external FEL seeding has proven to be a reliable method to do so. At FLASH, an experimental setup to test several different external seeding methods has been installed since 2010. After successful demonstration of direct seeding at 38 nm, the setup is now being commissioned to operate in HGHG and EEHG mode. Furthermore, other studies on laser induced effects on the electron beam dynamics will be performed. Beside the experimental activities, a design for the seeding option for the FLASH2 beamline is currently under investigation. The goal for that is to develop a concept which is compatible with the operation of FLASH1 and which satisfies the high demands of the future user community. In this contribution, we give an overview of the activities on FEL seeding at FLASH.

MOP094

Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure

272

N. Ekanayake, S. Ackermann
DESY, Hamburg, Germany
S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity.
Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

THP076

Measurements of the Timing Stability at the FLASH1 Seeding Experiment

913

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach, M. Wieland
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, H. Dachraoui, N. Ekanayake, B. Faatz, M. Felber, K. Honkavaara, T. Laarmann, J.M. Mueller, H. Schlarb, S. Schreiber, S. Schulz
DESY, Hamburg, Germany
G. Angelova Hamberg
Uppsala University, Uppsala, Sweden
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany
P.M. Salen, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4 and 05K13PE3 and the German Research Foundation programme graduate school 1355.
For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.

Paper	Title	Page
MOP060	Demonstration of SASE Suppression Through a Seeded Microbunching Instability	177
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP089	Overview of FEL Seeding Activities at FLASH
	J. Bödewadt, S. Ackermann, R.W. Aßmann, N. Ekanayake, B. Faatz, G. Feng, I. Hartl, R. Ivanov, T. Laarmann, J.M. Mueller, T. Tanikawa DESY, Hamburg, Germany S. Ackermann, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Roßbach Uni HH, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	The free-electron laser facility FLASH at DESY operates since several years in SASE mode, delivering high-intensity FEL pulses in the extreme ultra violet and soft x-ray wavelength range for users. In order to get more control of the characteristics of the FEL pulses external FEL seeding has proven to be a reliable method to do so. At FLASH, an experimental setup to test several different external seeding methods has been installed since 2010. After successful demonstration of direct seeding at 38 nm, the setup is now being commissioned to operate in HGHG and EEHG mode. Furthermore, other studies on laser induced effects on the electron beam dynamics will be performed. Beside the experimental activities, a design for the seeding option for the FLASH2 beamline is currently under investigation. The goal for that is to develop a concept which is compatible with the operation of FLASH1 and which satisfies the high demands of the future user community. In this contribution, we give an overview of the activities on FEL seeding at FLASH.

MOP094	Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure	272
	N. Ekanayake, S. Ackermann DESY, Hamburg, Germany S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath Uni HH, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany
	Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity. Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

THP076	Measurements of the Timing Stability at the FLASH1 Seeding Experiment	913
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach, M. Wieland Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, H. Dachraoui, N. Ekanayake, B. Faatz, M. Felber, K. Honkavaara, T. Laarmann, J.M. Mueller, H. Schlarb, S. Schreiber, S. Schulz DESY, Hamburg, Germany G. Angelova Hamberg Uppsala University, Uppsala, Sweden K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany P.M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4 and 05K13PE3 and the German Research Foundation programme graduate school 1355. For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.