FEL2015 - List of Keywords (polarization)

Paper	Title	Other Keywords	Page
MOP008	Theoretical Computation of the Polarization Characteristics of an X-Ray Free-Electron Laser with Planar Undulator	undulator, FEL, electron, radiation	38
	G. Geloni XFEL. EU, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λ_w²/(4 pi L_g)², where λ_w is the length of the undulator period and L_g is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λ_w³/(4 pi L_g)³ and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.
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MOP042	All-Fiber Approach to Long-Term Stable Timing Distribution System	timing, laser, 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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MOP070	Harmonic Generation in Two Orthogonal Undulators	undulator, electron, radiation, simulation	200
	N.S. Mirian UVSOR, Okazaki, Japan
	In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.
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TUP053	Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion	FEL, undulator, radiation, diagnostics	486
	W.M. Fawley, E. Allaria, E. Ferrari Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy
	Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators. [1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013). [2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014).
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WEP082	High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses	radiation, electron, timing, 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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WEP087	Smith-Purcell Radiation from Microbunched Beams Modulated after Passing the Undulators in FELs	radiation, FEL, target, undulator	752
	A. Potylitsyn TPU, Tomsk, Russia D.Yu. Sergeeva, M.N. Strikhanov, A.A. Tishchenko MEPhI, Moscow, Russia
	We suggest using the Smith-Purcell effect from microbunched beams modulated after passing the undulators in FELs as an extra source of monochromatic radiation. We investigate theoretically characteristics of Smith-Purcell radiation in THz and X-ray frequency regions for two types of distribution of the particles in the beam. The expression for spectral-angular distribution of such radiation is obtained and analyzed, both for fully and partially modulated beams. The intensity of Smith-Purcell radiation is shown to be able to increase both due to the periodicity of the beam and the periodicity of the target. The numerical results prove that such radiation source can be an effective instrument for different FEL users, supplementary for the main FEL source.
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WED01	Commissioning of the Delta Polarizing Undulator at LCLS	undulator, radiation, bunching, electron	757
	H.-D. Nuhn, S.D. Anderson, R.N. Coffee, Y. Ding, Z. Huang, M. Ilchen, Yu.I. Levashov, A.A. Lutman, J.P. MacArthur, A. Marinelli, S.P. Moeller, F. Peters, Z.R. Wolf SLAC, Menlo Park, California, USA J. Buck XFEL. EU, Hamburg, Germany G. Hartmann, J. Viefhaus DESY, Hamburg, Germany A.O. Lindahl University of Gothenburg, Gothenburg, Sweden A.B. Temnykh Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work was supported by U.S. DOE, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A.B. Temnykh is supported U.S. National Science Foundation awards DMR-0807731 and DMR-DMR-0936384. The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators, which provides only limited taper capability and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new 3.2-m-long compact undulator (based on the Cornell University fixed-gap Delta design) has been developed and installed as the last LCLS undulator segment (U33) in October 2014. The Delta undulator provides full control of the polarization degree and K parameter through array position adjustments. Used on its own, it produces fully polarized spontaneous radiation in the selected state (linear, circular or elliptical). To increase the output power by orders of magnitude, the electron beam is micro-bunched by several (5-15) upstream LCLS undulator segments operated in the linear FEL regime. This micro-bunching process produces horizontally linear polarized (background) radiation. This unwanted radiation component has been greatly reduced by a reversed taper configuration, as suggested by Schneidmiller. Full elimination of the linear polarized component was achieved through spatial separation combined with transverse collimation. The paper will describe the methods tested during commissioning and will also present results of polarization measurements showing high degrees of circular polarization in the soft x-ray wavelength range.
	Slides WED01 [10.165 MB]
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Paper

Title

Other Keywords

Page

MOP008

Theoretical Computation of the Polarization Characteristics of an X-Ray Free-Electron Laser with Planar Undulator

undulator, FEL, electron, radiation

38

G. Geloni
XFEL. EU, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λ_w²/(4 pi L_g)², where λ_w is the length of the undulator period and L_g is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λ_w³/(4 pi L_g)³ and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.

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MOP042

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

timing, laser, 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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MOP070

Harmonic Generation in Two Orthogonal Undulators

undulator, electron, radiation, simulation

200

N.S. Mirian
UVSOR, Okazaki, Japan

In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.

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TUP053

Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion

FEL, undulator, radiation, diagnostics

486

W.M. Fawley, E. Allaria, E. Ferrari
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy

Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators.
[1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013).
[2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014).

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WEP082

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

radiation, electron, timing, 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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WEP087

Smith-Purcell Radiation from Microbunched Beams Modulated after Passing the Undulators in FELs

radiation, FEL, target, undulator

752

A. Potylitsyn
TPU, Tomsk, Russia
D.Yu. Sergeeva, M.N. Strikhanov, A.A. Tishchenko
MEPhI, Moscow, Russia

We suggest using the Smith-Purcell effect from microbunched beams modulated after passing the undulators in FELs as an extra source of monochromatic radiation. We investigate theoretically characteristics of Smith-Purcell radiation in THz and X-ray frequency regions for two types of distribution of the particles in the beam. The expression for spectral-angular distribution of such radiation is obtained and analyzed, both for fully and partially modulated beams. The intensity of Smith-Purcell radiation is shown to be able to increase both due to the periodicity of the beam and the periodicity of the target. The numerical results prove that such radiation source can be an effective instrument for different FEL users, supplementary for the main FEL source.

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

WED01

Commissioning of the Delta Polarizing Undulator at LCLS

undulator, radiation, bunching, electron

757

H.-D. Nuhn, S.D. Anderson, R.N. Coffee, Y. Ding, Z. Huang, M. Ilchen, Yu.I. Levashov, A.A. Lutman, J.P. MacArthur, A. Marinelli, S.P. Moeller, F. Peters, Z.R. Wolf
SLAC, Menlo Park, California, USA
J. Buck
XFEL. EU, Hamburg, Germany
G. Hartmann, J. Viefhaus
DESY, Hamburg, Germany
A.O. Lindahl
University of Gothenburg, Gothenburg, Sweden
A.B. Temnykh
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work was supported by U.S. DOE, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A.B. Temnykh is supported U.S. National Science Foundation awards DMR-0807731 and DMR-DMR-0936384.
The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators, which provides only limited taper capability and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new 3.2-m-long compact undulator (based on the Cornell University fixed-gap Delta design) has been developed and installed as the last LCLS undulator segment (U33) in October 2014. The Delta undulator provides full control of the polarization degree and K parameter through array position adjustments. Used on its own, it produces fully polarized spontaneous radiation in the selected state (linear, circular or elliptical). To increase the output power by orders of magnitude, the electron beam is micro-bunched by several (5-15) upstream LCLS undulator segments operated in the linear FEL regime. This micro-bunching process produces horizontally linear polarized (background) radiation. This unwanted radiation component has been greatly reduced by a reversed taper configuration, as suggested by Schneidmiller. Full elimination of the linear polarized component was achieved through spatial separation combined with transverse collimation. The paper will describe the methods tested during commissioning and will also present results of polarization measurements showing high degrees of circular polarization in the soft x-ray wavelength range.

Slides WED01 [10.165 MB]

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