FEL2012 - List of Authors (Schlarb, H.)

Paper

Title

Page

Laser Pulse Train Management with an Acousto-optic Modulator

189

M. Groß, H.-J. Grabosch, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M. Khojoyan, G. Klemz, G. Kourkafas, M. Krasilnikov, K. Kusoljariyakul, J. Li, M. Mahgoub, D. Malyutin, B. Marchetti, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany
D. Richter
HZB, Berlin, Germany
H. Schlarb, S. Schreiber
DESY, Hamburg, Germany

Photo injector laser systems for linac based FELs often have the capability of generating pulse trains with an adjustable length. For example, the currently installed laser at the Photo Injector Test Facility at DESY, Zeuthen Site (PITZ) can generate pulse trains containing up to 800 pulses. Repetition frequencies are 10 Hz for the pulse trains and 1 MHz for the pulses within a train, respectively. Mostly due to thermal effects caused by absorption in amplifier and frequency doubling crystals, pulse properties are changing slightly within a pulse train and also shot-to-shot, depending on the pulse train length. To increase stability and repeatability of the laser it is desirable to run it under constant conditions. To achieve this while still being able to freely choose pulse patterns a pulse picker to sort the wanted from the unwanted pulses can be installed at the laser output. A promising candidate for this functionality is an acousto-optic modulator which currently is being tested at PITZ. First experimental results will be presented and discussed towards the possibility of including this device into an FEL photo injector.

TUOAI01

First Direct Seeding at 38nm

197

C. Lechner, A. Azima, J. Bödewadt, M. Drescher, E. Hass, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Rehders, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian, M. Wieland
Uni HH, Hamburg, Germany
S. Ackermann, S. Bajt, H. Dachraoui, H. Delsim-Hashemi, S. Düsterer, B. Faatz, K. Honkavaara, T. Laarmann, M. Mittenzwey, H. Schlarb, S. Schreiber, L. Schroedter, M. Tischer
DESY, Hamburg, Germany
F. Curbis
MAX-lab, Lund, Sweden
R. Ischebeck
PSI, Villigen PSI, Switzerland
S. Khan
DELTA, Dortmund, Germany
V. Wacker
University of Hamburg, Hamburg, Germany

Funding: The project is supported by the Federal Ministry of Education and Research of Germany under contract No. 05 K10GU1 and by the German Research Foundation programme graduate school 1355.
The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm.

Slides TUOAI01 [11.553 MB]

TUOB03

Complete Ultrafast X-ray Pulse Characterization at FELs

A.L. Cavalieri, H. Bromberger, I. Grguras, S. Huber
CFEL, Hamburg, Germany
C. Behrens, S. Düsterer, H. Schlarb
DESY, Hamburg, Germany
C. Bostedt, J.D. Bozek, R.N. Coffee, Y.T. Ding, J.B. Hastings, M.C. Hoffmann, S. Schorb
SLAC, Menlo Park, California, USA
J.T. Costello
DCU, Dublin, Republic of Ireland
L.F. DiMauro
Ohio State University, USA
G. Doumy
ANL, Argonne, USA
W. Helml, R. Kienberger, A.R. Maier, W. Schweinberger
MPQ, Garching, Munich, Germany
N.M. Kabachnik, T. Mazza, M. Meyer, T. Tschentscher
XFEL. EU, Hamburg, Germany
A.K. Kazansky
UPV-EHU, Leioa, Spain

The ability to fully characterize X-ray pulses from free electron-lasers will underpin their exploitation in experiments ranging from single-molecule imaging to extreme timescale X-ray science. This issue is especially acute when confronted with the characteristics of current generation FELs operating on the principle of SASE, as most parameters fluctuate strongly from pulse to pulse. Here, we have extended the techniques of attosecond metrology with the use of single-cycle terahertz (THz) pulses, allowing for simultaneous, in-line, single-shot measurement of both the arrival time and temporal profile of FEL pulses on an absolute scale. The technique is non-invasive and could be incorporated in pump-probe experiments, eventually leading to characterization before and after interaction with most sample environments. Optical-laser-driven THz streaking measurements, revealing X-ray pulse structure shorter than 50 fs FWHM in the soft X-ray regime at FLASH and in the ~ keV range at LCLS will be discussed. With clear potential for improvement in resolution to the sub-10 fs regime, this method will ultimately allow for characterization of the shortest predicted few-femtosecond FEL pulses.

Slides TUOB03 [15.857 MB]

TUPD13

Progress Towards HGHG and EEHG at FLASH

257

K.E. Hacker, C. Behrens, H. Schlarb
DESY, Hamburg, Germany
G. Angelova Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden
A. Azima, J. Bödewadt
Uni HH, Hamburg, Germany
S. Khan, R. Molo
DELTA, Dortmund, Germany
P. Salén, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden

Funding: BMBF 05K10PE1 and DESY
New infrastructure was built at FLASH to enable 30-100 fs long, milliJoule pulses of 270 nm light to seed the electron beam with HGHG and EEHG techniques, targeting wavelengths in the range from 10 nm to 40 nm. HGHG, or High Gain Harmonic Generation, and EEHG, or Echo-Enabled Harmonic Generation, utilize an external laser together with chicanes and undulators in order to generate a bunched beam which will radiate in a subsequent undulator. In the case of HGHG, the beam is bunched at the seed laser wavelength, radiating harmonics thereof in the radiator. In the case of EEHG, the beam is bunched at a harmonic of the seed wavelength, radiating that same harmonic in the radiator. The properties of the setup, commissioning difficulties and the inital attempts at HGHG seeding at 38.5 nm will be described.

TUPD35

Femtosecond Level Synchronization of a Linac based Super-radiant THz Facility

313

M. Kuntzsch, M. Gensch, U. Lehnert, F. Röser
HZDR, Dresden, Germany
M. Bousonville, H. Schlarb, N. Stojanovic, S. Vilcins
DESY, Hamburg, Germany

The superconducting radiofrequency (SRF) electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded with an SRF Gun and a femtosecond (fs) electron beamline to enable continuous wave operation with bunch charges of up to 1 nC and bunch durations down to 100 fs (RMS). The new femtosecond electron beamline will be used to drive two coherent THz sources and one X-ray source based on Thomson scattering. The two different THz sources, one narrow bandwidth undulator source and one broad bandwidth coherent transition/diffraction source, are guided into a dedicated THz Laboratory where they can be combined with various fs-laser systems. For the planned THz pump laser probe experiments, synchronization of the external pump-probe lasers on the fs- level is essential. Our approach is based on an optical synchronization system, adapted from a similar system installed at FLASH [*]. That system will be installed in collaboration between DESY and HZDR. In this contribution we will discuss the layout of the synchronization scheme and first ideas for measurements of the arrival time jitter of the THz pulses to evaluate the achieved degree of timing stability.
* F.Loehl, H.Schlarb et. al."Sub-10 femtosecond stabilization of a fiber-link using a balanced optical cross-correlator", proceedings of PAC2007, Albuquerque, USA, JUN 25-29 2007, FR0AC04.

WEPD07

Status of the FLASH II Project

381

K. Honkavaara, S. Ackermann, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, B. Faatz, M. Felber, J. Feldhaus, N. Golubeva, M. Körfer, M. Kuhlmann, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, N. Mildner, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Remde, H. Schlarb, B. Schmidt, M. Schmitz, M. Scholz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, N. Stojanovic, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig, T. Wohlenberg
DESY, Hamburg, Germany
M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner
Uni HH, Hamburg, Germany
F. Tavella
HIJ, Jena, Germany

The extension of the FLASH facility at DESY (Hamburg, Germany) - FLASH II Project - is under way. The extension includes a second undulator line with variable gap undulators to allow a more flexible operation, and a new experimental hall for photon experiments. The present FLASH linac will drive the both undulator beamlines. Civil construction of the new buildings has been started in autumn 2011 continuing in several steps until early 2013. The design of the new beamline including the extraction from the FLASH linac and the undulator is mostly finished, and the manufacturing of the components is under way. The mounting of the beamline will start in autumn 2012, and the commissioning with beam is scheduled for second half of 2013. We report here the design of the different phases of the project including the time schedule up to the first user operation.

THPD33

Generation of Ultra-short Electron Bunches at FLASH

610

J. Rönsch-Schulenburg, E. Hass, A. Kuhl, T. Plath, M. Rehders, J. Roßbach
Uni HH, Hamburg, Germany
A. Angelovski, R. Jakoby, A. Penirschke
TU Darmstadt, Darmstadt, Germany
N. Baboi, M. Bousonville, M.K. Czwalinna, C. Gerth, K. Klose, T. Limberg, U. Mavrič, H. Schlarb, B. Schmidt, S. Schreiber, B. Steffen, C. Sydlo, S. Vilcins, S. Wesch
DESY, Hamburg, Germany
S. Schnepp, T. Weiland
TEMF, TU Darmstadt, Darmstadt, Germany

Funding: The work is supported by German Federal Ministry of Education and Research (BMBF) within Joint Project - FSP 301 under the contract number 05K10GU2.
In order to produce radiation pulses of a few femtoseconds at FELs like FLASH, different concepts have been proposed. Probably the most robust method is to create an electron bunch, which is in the most extreme case as short as one longitudinal optical mode. For FLASH this translates into a bunch length of a few micrometers only. In order to mitigate space charge effects, the bunch charge needs to be about 20 pC. The technical requirements to achieve this goal are discussed. This includes beam dynamics studies to optimize the injection and compression of small charge electron bunches. A reduced photo injector laser pulse duration helps to relax the RF tolerance which scales linear with the compression factor. A new photo injector laser with sub-picosecond pulse duration in combination with a stretcher is used to optimize the initial bunch length. The commissioning of the new laser system and first experiments are described. Limitations of the presently available electron beam diagnostics at FLASH for short, low charge bunches are analyzed. Improvements of the longitudinal phase space diagnostics and the commissioning of a more sensitive beam arrival time monitor are described.

THPD37

Beam Dynamic Studies for the Generation of Short SASE Pulses at FLASH

614

M. Rehders, J. Roßbach
Uni HH, Hamburg, Germany
J. Rönsch-Schulenburg
CFEL, Hamburg, Germany
H. Schlarb, S. Schreiber
DESY, Hamburg, Germany

Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301.
Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. In the ideal case a bunch charge of 20pC is sufficient for the generation of such short bunches. A shorter bunch duration directly at the photo-cathode helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and collective effects. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode though the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. A comparison of the beam dynamics simulations with measurements is presented in this contribution. The expected SASE pulses are being simulated with the Genesis code.

Paper	Title	Page
MOPD61	Laser Pulse Train Management with an Acousto-optic Modulator	189
	M. Groß, H.-J. Grabosch, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M. Khojoyan, G. Klemz, G. Kourkafas, M. Krasilnikov, K. Kusoljariyakul, J. Li, M. Mahgoub, D. Malyutin, B. Marchetti, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany D. Richter HZB, Berlin, Germany H. Schlarb, S. Schreiber DESY, Hamburg, Germany
	Photo injector laser systems for linac based FELs often have the capability of generating pulse trains with an adjustable length. For example, the currently installed laser at the Photo Injector Test Facility at DESY, Zeuthen Site (PITZ) can generate pulse trains containing up to 800 pulses. Repetition frequencies are 10 Hz for the pulse trains and 1 MHz for the pulses within a train, respectively. Mostly due to thermal effects caused by absorption in amplifier and frequency doubling crystals, pulse properties are changing slightly within a pulse train and also shot-to-shot, depending on the pulse train length. To increase stability and repeatability of the laser it is desirable to run it under constant conditions. To achieve this while still being able to freely choose pulse patterns a pulse picker to sort the wanted from the unwanted pulses can be installed at the laser output. A promising candidate for this functionality is an acousto-optic modulator which currently is being tested at PITZ. First experimental results will be presented and discussed towards the possibility of including this device into an FEL photo injector.

TUOAI01	First Direct Seeding at 38nm	197
	C. Lechner, A. Azima, J. Bödewadt, M. Drescher, E. Hass, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Rehders, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian, M. Wieland Uni HH, Hamburg, Germany S. Ackermann, S. Bajt, H. Dachraoui, H. Delsim-Hashemi, S. Düsterer, B. Faatz, K. Honkavaara, T. Laarmann, M. Mittenzwey, H. Schlarb, S. Schreiber, L. Schroedter, M. Tischer DESY, Hamburg, Germany F. Curbis MAX-lab, Lund, Sweden R. Ischebeck PSI, Villigen PSI, Switzerland S. Khan DELTA, Dortmund, Germany V. Wacker University of Hamburg, Hamburg, Germany
	Funding: The project is supported by the Federal Ministry of Education and Research of Germany under contract No. 05 K10GU1 and by the German Research Foundation programme graduate school 1355. The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm.
	Slides TUOAI01 [11.553 MB]

TUOB03	Complete Ultrafast X-ray Pulse Characterization at FELs
	A.L. Cavalieri, H. Bromberger, I. Grguras, S. Huber CFEL, Hamburg, Germany C. Behrens, S. Düsterer, H. Schlarb DESY, Hamburg, Germany C. Bostedt, J.D. Bozek, R.N. Coffee, Y.T. Ding, J.B. Hastings, M.C. Hoffmann, S. Schorb SLAC, Menlo Park, California, USA J.T. Costello DCU, Dublin, Republic of Ireland L.F. DiMauro Ohio State University, USA G. Doumy ANL, Argonne, USA W. Helml, R. Kienberger, A.R. Maier, W. Schweinberger MPQ, Garching, Munich, Germany N.M. Kabachnik, T. Mazza, M. Meyer, T. Tschentscher XFEL. EU, Hamburg, Germany A.K. Kazansky UPV-EHU, Leioa, Spain
	The ability to fully characterize X-ray pulses from free electron-lasers will underpin their exploitation in experiments ranging from single-molecule imaging to extreme timescale X-ray science. This issue is especially acute when confronted with the characteristics of current generation FELs operating on the principle of SASE, as most parameters fluctuate strongly from pulse to pulse. Here, we have extended the techniques of attosecond metrology with the use of single-cycle terahertz (THz) pulses, allowing for simultaneous, in-line, single-shot measurement of both the arrival time and temporal profile of FEL pulses on an absolute scale. The technique is non-invasive and could be incorporated in pump-probe experiments, eventually leading to characterization before and after interaction with most sample environments. Optical-laser-driven THz streaking measurements, revealing X-ray pulse structure shorter than 50 fs FWHM in the soft X-ray regime at FLASH and in the ~ keV range at LCLS will be discussed. With clear potential for improvement in resolution to the sub-10 fs regime, this method will ultimately allow for characterization of the shortest predicted few-femtosecond FEL pulses.
	Slides TUOB03 [15.857 MB]

TUPD13	Progress Towards HGHG and EEHG at FLASH	257
	K.E. Hacker, C. Behrens, H. Schlarb DESY, Hamburg, Germany G. Angelova Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden A. Azima, J. Bödewadt Uni HH, Hamburg, Germany S. Khan, R. Molo DELTA, Dortmund, Germany P. Salén, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
	Funding: BMBF 05K10PE1 and DESY New infrastructure was built at FLASH to enable 30-100 fs long, milliJoule pulses of 270 nm light to seed the electron beam with HGHG and EEHG techniques, targeting wavelengths in the range from 10 nm to 40 nm. HGHG, or High Gain Harmonic Generation, and EEHG, or Echo-Enabled Harmonic Generation, utilize an external laser together with chicanes and undulators in order to generate a bunched beam which will radiate in a subsequent undulator. In the case of HGHG, the beam is bunched at the seed laser wavelength, radiating harmonics thereof in the radiator. In the case of EEHG, the beam is bunched at a harmonic of the seed wavelength, radiating that same harmonic in the radiator. The properties of the setup, commissioning difficulties and the inital attempts at HGHG seeding at 38.5 nm will be described.

TUPD35	Femtosecond Level Synchronization of a Linac based Super-radiant THz Facility	313
	M. Kuntzsch, M. Gensch, U. Lehnert, F. Röser HZDR, Dresden, Germany M. Bousonville, H. Schlarb, N. Stojanovic, S. Vilcins DESY, Hamburg, Germany
	The superconducting radiofrequency (SRF) electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded with an SRF Gun and a femtosecond (fs) electron beamline to enable continuous wave operation with bunch charges of up to 1 nC and bunch durations down to 100 fs (RMS). The new femtosecond electron beamline will be used to drive two coherent THz sources and one X-ray source based on Thomson scattering. The two different THz sources, one narrow bandwidth undulator source and one broad bandwidth coherent transition/diffraction source, are guided into a dedicated THz Laboratory where they can be combined with various fs-laser systems. For the planned THz pump laser probe experiments, synchronization of the external pump-probe lasers on the fs- level is essential. Our approach is based on an optical synchronization system, adapted from a similar system installed at FLASH []. That system will be installed in collaboration between DESY and HZDR. In this contribution we will discuss the layout of the synchronization scheme and first ideas for measurements of the arrival time jitter of the THz pulses to evaluate the achieved degree of timing stability. F.Loehl, H.Schlarb et. al."Sub-10 femtosecond stabilization of a fiber-link using a balanced optical cross-correlator", proceedings of PAC2007, Albuquerque, USA, JUN 25-29 2007, FR0AC04.

WEPD07	Status of the FLASH II Project	381
	K. Honkavaara, S. Ackermann, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, B. Faatz, M. Felber, J. Feldhaus, N. Golubeva, M. Körfer, M. Kuhlmann, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, N. Mildner, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Remde, H. Schlarb, B. Schmidt, M. Schmitz, M. Scholz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, N. Stojanovic, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig, T. Wohlenberg DESY, Hamburg, Germany M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner Uni HH, Hamburg, Germany F. Tavella HIJ, Jena, Germany
	The extension of the FLASH facility at DESY (Hamburg, Germany) - FLASH II Project - is under way. The extension includes a second undulator line with variable gap undulators to allow a more flexible operation, and a new experimental hall for photon experiments. The present FLASH linac will drive the both undulator beamlines. Civil construction of the new buildings has been started in autumn 2011 continuing in several steps until early 2013. The design of the new beamline including the extraction from the FLASH linac and the undulator is mostly finished, and the manufacturing of the components is under way. The mounting of the beamline will start in autumn 2012, and the commissioning with beam is scheduled for second half of 2013. We report here the design of the different phases of the project including the time schedule up to the first user operation.

THPD33	Generation of Ultra-short Electron Bunches at FLASH	610
	J. Rönsch-Schulenburg, E. Hass, A. Kuhl, T. Plath, M. Rehders, J. Roßbach Uni HH, Hamburg, Germany A. Angelovski, R. Jakoby, A. Penirschke TU Darmstadt, Darmstadt, Germany N. Baboi, M. Bousonville, M.K. Czwalinna, C. Gerth, K. Klose, T. Limberg, U. Mavrič, H. Schlarb, B. Schmidt, S. Schreiber, B. Steffen, C. Sydlo, S. Vilcins, S. Wesch DESY, Hamburg, Germany S. Schnepp, T. Weiland TEMF, TU Darmstadt, Darmstadt, Germany
	Funding: The work is supported by German Federal Ministry of Education and Research (BMBF) within Joint Project - FSP 301 under the contract number 05K10GU2. In order to produce radiation pulses of a few femtoseconds at FELs like FLASH, different concepts have been proposed. Probably the most robust method is to create an electron bunch, which is in the most extreme case as short as one longitudinal optical mode. For FLASH this translates into a bunch length of a few micrometers only. In order to mitigate space charge effects, the bunch charge needs to be about 20 pC. The technical requirements to achieve this goal are discussed. This includes beam dynamics studies to optimize the injection and compression of small charge electron bunches. A reduced photo injector laser pulse duration helps to relax the RF tolerance which scales linear with the compression factor. A new photo injector laser with sub-picosecond pulse duration in combination with a stretcher is used to optimize the initial bunch length. The commissioning of the new laser system and first experiments are described. Limitations of the presently available electron beam diagnostics at FLASH for short, low charge bunches are analyzed. Improvements of the longitudinal phase space diagnostics and the commissioning of a more sensitive beam arrival time monitor are described.

THPD37	Beam Dynamic Studies for the Generation of Short SASE Pulses at FLASH	614
	M. Rehders, J. Roßbach Uni HH, Hamburg, Germany J. Rönsch-Schulenburg CFEL, Hamburg, Germany H. Schlarb, S. Schreiber DESY, Hamburg, Germany
	Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301. Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. In the ideal case a bunch charge of 20pC is sufficient for the generation of such short bunches. A shorter bunch duration directly at the photo-cathode helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and collective effects. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode though the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. A comparison of the beam dynamics simulations with measurements is presented in this contribution. The expected SASE pulses are being simulated with the Genesis code.