FEL2015 - List of Keywords (timing)

Paper	Title	Other Keywords	Page
MOP036	Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator	laser, detector, FEL, electron	105
	H. Yang, C. Jeon, K. Jung, J. Kim KAIST, Daejeon, Republic of Korea H. Chung Korea University Sejong Campus, Sejong, Republic of Korea B. Han, Y.U. Jeong KAERI, Daejon, Republic of Korea
	Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.
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MOP042	All-Fiber Approach to Long-Term Stable Timing Distribution System	laser, polarization, coupling, optics	122
	M. Xin, K. Safak, F.X. Kaernter DESY, Hamburg, Germany P.T. Callahan, M.Y. Peng MIT, Cambridge, Massachusetts, USA
	High precision timing distribution systems are critical for free-electron lasers (FELs). Real facilities such as FLASH and the European XFEL need fiber networks consisting of 20 or more timing links, which require tremendous attention to the alignment and stability of the free-space optics to minimize timing-drifts induced by beam pointing instabilities. This situation also necessitates preamplification of the master laser output to overcome excessive free-space to fiber coupling losses to provide adequate power for all timing links. Recently, we have developed integrated, fiber-coupled balanced optical cross-correlators (FC-BOC) using periodically-poled KTiOPO4 (PPKTP) waveguides. These waveguides exhibit second harmonic conversion efficiencies 20 times higher than the bulk optical devices, which will decrease the power demand from the master laser and consequently support more timing links. Furthermore, the robustness and ease of implementation of these fiber-coupled devices will eliminate alignment-related problems observed in free-space optics. In this paper, we present an all-fiber implementation of a 3.5-km timing distribution system using FC-BOCs, over 200 hours operation without interruption. The remaining drift (<1 Hz) is only 3.3 fs RMS, and the integrated jitter above 1 Hz is kept below 0.7 fs, which is more than sufficient for an efficient FEL synchronization.
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MOP043	Influence of Environment Changes on Libera Sync 3 Long-term Stability	controls, detector, monitoring, operation	126
	S. Zorzut, M. Cargnelutti I-Tech, Solkan, Slovenia S. Hunziker PSI, Villigen PSI, Switzerland
	Libera Sync 3 can be used as a reference clock transfer system in the latest fourth generation light sources where the long-term stability is in the range of a few tens of femtoseconds of drift per day. The system has been developed in collaboration with the Paul Scherrer Institute (PSI) and first units are already tested in SwissFEL machine. In this article we present the influence of temperature and humidity changes on the long-term phase stability of the system.
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MOP047	The BINP HLS to Measure Vertical Changes on PAL-XFEL Buildings and Ground	survey, operation, experiment, alignment	133
	H. J. Choi, K.H. Gil, H.-S. Kang, S.H. Kim, K.W. Seo PAL, Pohang, Kyungbuk, Republic of Korea
	PAL-XFEL is being installed and will be completed by December of 2015 so that users can be supported beginning in 2016. PAL-XFEL equipment should continuously maintain the bunch beam parameter. To this end, PAL-XFEL equipment has to be kept precisely aligned. As a part of the process for installing PAL-XFEL, a surface geodetic network and the installation of a tunnel measurement network inside buildings is in preparation; additionally, the fiducialization of major equipment is underway. After PAL-XFEL equipment is optimized and aligned, if the ground and buildings go through vertical changes during operation, misalignment of equipments will cause errors in the electron beam trajectory, which will lead to changes to the beam parameter. For continuous and systemic measurement of vertical changes in buildings and to monitor ground subsidence (sinks) and uplift, the BINP Ultrasonic-type Hydrostatic Levelling System (HLS) is to be installed and operated in all sections of PAL-XFEL for linear accelerator, undulator and beam line. This study will introduce the operation principle, design concept and advantages (self-calibration) of BINP ULS Sensor, and will outline its installation plan and operation plan.
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TUP045	MTCA.4 Phase Detector for Femtosecond-Precision Laser Synchronization	laser, detector, controls, experiment	474
	E. Janas, M. Felber, M. Heuer, U. Mavrič, H. Schlarb DESY, Hamburg, Germany K. Czuba Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	For time-resolved experiments at FELs such as the European XFEL an accurate synchronization of the machine is essential. The required femtosecond- level synchronization we plan to achieve with an optical synchronization system, in which an inherent part is the master laser oscillator (MLO) locked to the electrical reference. At DESY we develop a custom rear transition module in MTCA.4 standard, which will allow for different techniques of phase detection between the optical and the electrical signal, as well as locking to an optical reference using a cross-correlator. In this paper we present the current status of the development, including two basic solutions for the detection to an RF. One of the methods incorporates an external drift free detector based on the so-called MZI setup. The other one employs the currently used downconverter scheme with subsequent improvements. The module can serve for locking a variety of lasers with different repetition rates.
	Poster TUP045 [4.010 MB]
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TUP049	Prototype of the Improved Electro-Optical Unit for the Bunch Arrival Time Monitors at FLASH and the European XFEL	laser, electron, electronics, pick-up	478
	H. Dinter, M.K. Czwalinna, C. Gerth, K.P. Przygoda, R. Rybaniec, H. Schlarb, C. Sydlo DESY, Hamburg, Germany
	At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems providing accurate timing stability for time-resolved pump-probe experiments and seeding schemes. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultra-short laser pulses. At both facilities, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into several segments for different SASE beam lines. Each of the segments will exhibit individual timing jitter characteristics since they are generated from different injector lasers and can be accelerated with individual energy gain settings. In this paper, we describe the recent improvements of the electro-optical unit developed for the bunch arrival time monitors to be installed in both facilities.
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TUP070	Energy Jitter Minimization at LCLS	linac, experiment, operation, simulation	523
	L. Wang, A.L. Benwell, A. Brachmann, W.S. Colocho, F.-J. Decker, Z. Huang, T.J. Maxwell, T. Tao, J.L. Turner SLAC, Menlo Park, California, USA
	The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively.
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WEP010	Development of Phonon Dynamics Measurement System by MIR-FEL and Pico-second Laser	FEL, laser, scattering, lattice	615
	T. Murata, T. Katsurayama, T. Kii, T. Konstantin, K. Masuda, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Zen Kyoto University, Kyoto, Japan K. Hachiya Kyoto University Graduate School of Energy Science, Kyoto, Japan K. Yoshida Kumamoto University, Department of Applied Chemistry and Biochemistry, Kumamoto, Japan
	Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.
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WEP023	Two Bunches with ns-Separation with LCLS	laser, experiment, photon, controls	634
	F.-J. Decker, S. Gilevich, Z. Huang, H. Loos, A. Marinelli, C.A. Stan, J.L. Turner, Z. Van Hoover, S. Vetter SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) delivers typically one bunch. Two bunches are interesting for pump / probe experiments. Two electron bunches with ps separation have been already produced using a split and delay in the laser which produces them on the gun cathode. Here we present the combination of two lasers with a combiner, this allows any time separation and is it limited to RF bucket spacing so far to about 40 ns limited by the setup of our beam containment system. Different beam energies were also provided and the most challenging part was a transverse separation of a few σs for the two beams. Although this setup was very jittery a successful user experiment was accomplished.
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WEP047	Femtosecond Timing Distribution at the European XFEL	laser, optics, FEL, electron	669
	C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack DESY, Hamburg, Germany S. Jabłoński Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.
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WEP082	High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses	polarization, radiation, electron, laser	739
	J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov KAERI, Daejon, Republic of Korea B.A. Gudkov, S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method. Phys. Rev. Lett. 110, 064805.
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Paper

Title

Other Keywords

Page

MOP036

Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator

laser, detector, FEL, electron

105

H. Yang, C. Jeon, K. Jung, J. Kim
KAIST, Daejeon, Republic of Korea
H. Chung
Korea University Sejong Campus, Sejong, Republic of Korea
B. Han, Y.U. Jeong
KAERI, Daejon, Republic of Korea

Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.

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MOP042

All-Fiber Approach to Long-Term Stable Timing Distribution System

laser, polarization, coupling, optics

122

M. Xin, K. Safak, F.X. Kaernter
DESY, Hamburg, Germany
P.T. Callahan, M.Y. Peng
MIT, Cambridge, Massachusetts, USA

High precision timing distribution systems are critical for free-electron lasers (FELs). Real facilities such as FLASH and the European XFEL need fiber networks consisting of 20 or more timing links, which require tremendous attention to the alignment and stability of the free-space optics to minimize timing-drifts induced by beam pointing instabilities. This situation also necessitates preamplification of the master laser output to overcome excessive free-space to fiber coupling losses to provide adequate power for all timing links. Recently, we have developed integrated, fiber-coupled balanced optical cross-correlators (FC-BOC) using periodically-poled KTiOPO4 (PPKTP) waveguides. These waveguides exhibit second harmonic conversion efficiencies 20 times higher than the bulk optical devices, which will decrease the power demand from the master laser and consequently support more timing links. Furthermore, the robustness and ease of implementation of these fiber-coupled devices will eliminate alignment-related problems observed in free-space optics. In this paper, we present an all-fiber implementation of a 3.5-km timing distribution system using FC-BOCs, over 200 hours operation without interruption. The remaining drift (<1 Hz) is only 3.3 fs RMS, and the integrated jitter above 1 Hz is kept below 0.7 fs, which is more than sufficient for an efficient FEL synchronization.

Export •

reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

MOP043

Influence of Environment Changes on Libera Sync 3 Long-term Stability

controls, detector, monitoring, operation

126

S. Zorzut, M. Cargnelutti
I-Tech, Solkan, Slovenia
S. Hunziker
PSI, Villigen PSI, Switzerland

Libera Sync 3 can be used as a reference clock transfer system in the latest fourth generation light sources where the long-term stability is in the range of a few tens of femtoseconds of drift per day. The system has been developed in collaboration with the Paul Scherrer Institute (PSI) and first units are already tested in SwissFEL machine. In this article we present the influence of temperature and humidity changes on the long-term phase stability of the system.

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MOP047

The BINP HLS to Measure Vertical Changes on PAL-XFEL Buildings and Ground

survey, operation, experiment, alignment

133

H. J. Choi, K.H. Gil, H.-S. Kang, S.H. Kim, K.W. Seo
PAL, Pohang, Kyungbuk, Republic of Korea

PAL-XFEL is being installed and will be completed by December of 2015 so that users can be supported beginning in 2016. PAL-XFEL equipment should continuously maintain the bunch beam parameter. To this end, PAL-XFEL equipment has to be kept precisely aligned. As a part of the process for installing PAL-XFEL, a surface geodetic network and the installation of a tunnel measurement network inside buildings is in preparation; additionally, the fiducialization of major equipment is underway. After PAL-XFEL equipment is optimized and aligned, if the ground and buildings go through vertical changes during operation, misalignment of equipments will cause errors in the electron beam trajectory, which will lead to changes to the beam parameter. For continuous and systemic measurement of vertical changes in buildings and to monitor ground subsidence (sinks) and uplift, the BINP Ultrasonic-type Hydrostatic Levelling System (HLS) is to be installed and operated in all sections of PAL-XFEL for linear accelerator, undulator and beam line. This study will introduce the operation principle, design concept and advantages (self-calibration) of BINP ULS Sensor, and will outline its installation plan and operation plan.

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TUP045

MTCA.4 Phase Detector for Femtosecond-Precision Laser Synchronization

laser, detector, controls, experiment

474

E. Janas, M. Felber, M. Heuer, U. Mavrič, H. Schlarb
DESY, Hamburg, Germany
K. Czuba
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

For time-resolved experiments at FELs such as the European XFEL an accurate synchronization of the machine is essential. The required femtosecond- level synchronization we plan to achieve with an optical synchronization system, in which an inherent part is the master laser oscillator (MLO) locked to the electrical reference. At DESY we develop a custom rear transition module in MTCA.4 standard, which will allow for different techniques of phase detection between the optical and the electrical signal, as well as locking to an optical reference using a cross-correlator. In this paper we present the current status of the development, including two basic solutions for the detection to an RF. One of the methods incorporates an external drift free detector based on the so-called MZI setup. The other one employs the currently used downconverter scheme with subsequent improvements. The module can serve for locking a variety of lasers with different repetition rates.

Poster TUP045 [4.010 MB]

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TUP049

Prototype of the Improved Electro-Optical Unit for the Bunch Arrival Time Monitors at FLASH and the European XFEL

laser, electron, electronics, pick-up

478

H. Dinter, M.K. Czwalinna, C. Gerth, K.P. Przygoda, R. Rybaniec, H. Schlarb, C. Sydlo
DESY, Hamburg, Germany

At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems providing accurate timing stability for time-resolved pump-probe experiments and seeding schemes. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultra-short laser pulses. At both facilities, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into several segments for different SASE beam lines. Each of the segments will exhibit individual timing jitter characteristics since they are generated from different injector lasers and can be accelerated with individual energy gain settings. In this paper, we describe the recent improvements of the electro-optical unit developed for the bunch arrival time monitors to be installed in both facilities.

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TUP070

Energy Jitter Minimization at LCLS

linac, experiment, operation, simulation

523

L. Wang, A.L. Benwell, A. Brachmann, W.S. Colocho, F.-J. Decker, Z. Huang, T.J. Maxwell, T. Tao, J.L. Turner
SLAC, Menlo Park, California, USA

The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively.

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reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

WEP010

Development of Phonon Dynamics Measurement System by MIR-FEL and Pico-second Laser

FEL, laser, scattering, lattice

615

T. Murata, T. Katsurayama, T. Kii, T. Konstantin, K. Masuda, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Zen
Kyoto University, Kyoto, Japan
K. Hachiya
Kyoto University Graduate School of Energy Science, Kyoto, Japan
K. Yoshida
Kumamoto University, Department of Applied Chemistry and Biochemistry, Kumamoto, Japan

Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.

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WEP023

Two Bunches with ns-Separation with LCLS

laser, experiment, photon, controls

634

F.-J. Decker, S. Gilevich, Z. Huang, H. Loos, A. Marinelli, C.A. Stan, J.L. Turner, Z. Van Hoover, S. Vetter
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) delivers typically one bunch. Two bunches are interesting for pump / probe experiments. Two electron bunches with ps separation have been already produced using a split and delay in the laser which produces them on the gun cathode. Here we present the combination of two lasers with a combiner, this allows any time separation and is it limited to RF bucket spacing so far to about 40 ns limited by the setup of our beam containment system. Different beam energies were also provided and the most challenging part was a transverse separation of a few σs for the two beams. Although this setup was very jittery a successful user experiment was accomplished.

Export •

reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

WEP047

Femtosecond Timing Distribution at the European XFEL

laser, optics, FEL, electron

669

C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack
DESY, Hamburg, Germany
S. Jabłoński
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.

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WEP082

High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses

polarization, radiation, electron, laser

739

J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov
KAERI, Daejon, Republic of Korea
B.A. Gudkov, S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [*] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method.
* Phys. Rev. Lett. 110, 064805.

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