Light Sources

Electric Field of Coherent Synchrotron Radiation Generated Using Laser
Bunch Slicing Technique
I. Katayama1, H. Shimosato2, M. Bito2, K. Furusawa2, M. Adachi3, 4, M. Shimada5, H. Zen3, 4,S. Kimura3, 4, N. Yamamoto6, M. Hosaka6, M. Katoh3, 4 and M. Ashida2, 7
1Interdisciplinary Research Center, Yokohama National Univ., Yokohama 240-8501, Japan
2
Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan
3
UVSOR, Institute of Molecular Science, Okazaki 444-8585, Japan
4
GraduateUniversities for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
5High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
6
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
7
PRESTO JST, Tokyo 102-0075, Japan

Terahertz region has been attracting much attention
in the viewpoints of solid-state physics, chemistry,and even biology, because its energy scale is offundamental importance for the phenomena occurringat or slightly below the room temperature. Recent
development of the ultrashort laser technology
enables us the generation and detection ofphase-locked terahertz waves, which is now applied
to the coherent spectroscopy such as terahertz
time-domain spectroscopy, and nonlinear terahertz
spectroscopy. Especially, the nonlinear terahertz
spectroscopy was difficult before the invention ofrecent laser-based terahertz technologies [1], which
requires intense and tunable terahertz light sources.
Coherent terahertz synchrotron radiation (CSR) is apromising light source for such nonlinear terahertz
spectroscopy because it potentially has ultrahighpower, and the spectrum can be tuned frombroadband to monochromatic in low-terahertz region[2]. In UVSOR, we recently demonstrated generationof CSR by applying the laser bunch slicing technique[2, 3]. However, the electric field detection of theCSR from laser bunch slicing has not been realized.
In this report, we show that the electric field of CSR
can be observed by using electro-optic sampling
method, and that the longitudinal density profile ofelectron bunches can be characterized by using theelectric field waveform [4].
We used a large mode-area photonic-crystal fiber todeliver the probe pulses to the detection port from thelaser systems for the laser bunch slicing. The outputof the seed oscillator was sent through the fiber andthen compressed to about 180 fs by using a
grating-pair compressor. The probe and CSR werefocused on an electro-optic crystal (ZnTe), and thepolarization rotation due to the CSR electric field wasdetected with electro-optic sampling method.
By using this method, it becomes possible tomeasure the electric field of the terahertz pulses asshown in Fig. 1(a). The observation of the pulsed
electric field means that phase of the CSR is indeed
very stable, which is a promising characteristic for thecoherent nonlinear terahertz spectroscopy. The
Fourier transform of the waveform is in good
agreement with the FTFIR measurement of the sameradiation at the same port [3, 4].
Because the generated CSR reflects thelongitudinal density profile of the electron bunch, wecan estimate it from the observed electric field profile.
Fig. 1(b) is the result of such calculation, illustrating
the formation of a dip structure in the electron bunch.
We reproduced the symmetric structure of the dip
expected in the theory [3], and showed that theduration of the dip depends on the duration of theslicing laser pulse [4].
In summary, we have demonstrated the electric field
detection of the CSR generated by using the laser
bunch slicing technique. From the observed electricfield waveform, it becomes possible to estimate thelongitudinal density distribution of electron bunches.
Therefore, the technique demonstrated in this study ispromising for monitoring bunch profiles, as well as
for coherent terahertz spectroscopy using CSR.
1.5(b)(a)p.c. 1 ps

p.c. 1 ps

p.c. 500 fs

p.c. 0.5 ps

0.5
t. l. 200 fs
0.0
n.c. 500 fs-0.5
n.c. 1 ps

Electron Density (a.u.)

Amplitude (a.u.)

1.0

t.l. 0.2 ps
n.c. 0.5 ps
n.c. 1 ps

-1.0
-1.5
05
10Time (ps)15-404
Time (ps)8Fig. 1. (a) Observed electric field waveforms of theCSR generated with various pulses of different chirp
and pulse durations: p.c.: positive chirp, t.l.: transfer
limited and n.c.: negative chirp. (b) Reconstructed
electron density profile of electron bunches.
[1] I. Katayama et al., Phys Rev. Lett. 108 (2012)
097401.
[2] S. Bielawski et al., Nat. Phys. 4 (2008) 390.
[3] M. Shimada et al., Jpn. J. Appl. Phys. 46 (2007)
7939.
[4] I. Katayama et al., Appl. Phys. Lett. 100 (2012)
111112.

31

Light Sources

Generation of Polarized Gamma Rays by Laser Compton Scattering
Y. Taira1, 2, M. Adachi3, H. Zen3, N. Yamamoto1, M. Hosaka1, K. Soda1 and M. Katoh3
1Graduate School of Engineering, Nagoya University, Nagoya 464-8603, JapanThe Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo 102-8472, Japan
3
UVSOR, Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan

2

Gamma rays with excellent features can begenerated via laser Compton scattering (LCS [1]),where incident laser photons are scattered by arelativistic electron beam circulating in an electron
storage ring. LCS gamma rays are tunable in energy,
quasi-monochromatic, intense, and highly polarized.
Highly polarized gamma rays can be generated via
LCS because gamma rays preserve polarization of anincident laser. Circularly polarized gamma rays areused in development polarized positron beam for
future electron-positron linear colliders and solid statephysics using magnetic Compton scattering. Linearlypolarized gamma rays are used in nuclear science.
In this paper, we have demonstrated that the spatial
image of the polarized gamma rays is reflected in thepolarization effect and have evaluated the degree of
linear polarization of LCS gamma rays.
The point of collision between the electron beamand the laser was in a vacuum chamber along astraight section. Linearly and circularly polarizedlaser was injected into the electron beam from thehorizontal 90-degree direction. The polarization wascontrolled by a wave plate. The spatial profile of thegamma rays was recorded with an imaging plate(BAS-IP MS) located 5.4 m away from the collision
point.
Figures 1 and 2 show the spatial images of LCS
gamma rays generated by linearly (horizontaldirection) and circularly polarized laser, respectively.
For the linear polarization, the root mean square (rms)of the LCS gamma rays is 0.245 mrad and 0.300 mrad
along the horizonrtal (x) and vertical (y) direction,respectively. For the circular polarization, the rms of
the LCS gamma rays is 0.294 mrad and 0.261 mrad
along the x and y direction, respectively.
The spatial distribution was calculated using aMonte Carlo simulation code, EGS5. In thissimulation, the divergence, and spatial distribution of
the electron beam were included in the calculation.
The rms of the linearly polarized gamma rays is 0.227
mrad and 0.282 mrad along the x and y direction,respectively. The divergence is lower along thehorizontal direction due to polarization effects. Therms of the circularly polarized gamma rays is 0.261
mrad and 0.230 mrad along the x and y direction,respectively. The divergence is lower along thevertical direction due to spatial distribution of theelectron beam.
We also calculated the spatial distribution of LCS
gamma rays with different degree of linearpolarization. The degree of linear polarization of LCS
gamma rays shown in Fig. 1 was found to be further

than 88 % by comparing the ratio of the rms along thex and y directions between the experimental data andcalculated values.

Fig. 1. Spatial image of LCS gamma rays generated
by linearly polarized laser.

Fig. 2. Spatial image of LCS gamma rays generated
by circularly polarized laser.
[1] J. Stepanek, Nucl. Instr. and Meth. A 412 (1998)
174.

32

Light Sources

Consideration on Using Higher Harmonics of Ti:Sa Laser for Coherent
Harmonic Generation at UVSOR
N. Wasa1, M. Hosaka2, Y. Uematsu1, S. Sekita1, N. Yamamoto2, Y. Takashima1, 2, M. Adachi3,H. Zen3, S. Tanaka3 and M. Katoh3
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Nagoya University Synchrotron Radiation Research Center, Nagoya 464-8603, Japan
3UVSOR, Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan

2efficiency and properties of the 2nd harmonics from
non-linear crystal. No-linear crystals of BBO ofthickness of 0.1 mm, 0.5 mm, 1 mm and 2 mm areirradiated by a mode-lock Ti:Sa laser with 2.5 mJ
pulse energy and 100 fsec. The measured efficiencyof 2nd harmonics is around 50 % for crystals withthickness more than 0.5 mm. We constructed acompact auto-correlator system to measure pulse
width of the 2nd harmonics [4]. Slightly increase of
pulse width is observed in the second harmonics, but
degradation to the peak power is small. We alsomeasured spectra of the 2nd harmonics using thecrystals and conclude that 0.5 mm thickness BBO is
the most suitable for our CHG experiment.
Near future we plan to make the CHG experimentusing 2nd harmonics of the Ti:Sa laser. We alsoplan to make basic experiment on production of 3rdand 4th harmonics for the CHG experiment.

Development of new coherent light sources using a
relativistic electron beam and laser is underway at theUVSOR storage ring. We have already succeeded ingeneration of coherent synchrotron radiation (CSR) in
THz region [1] and coherent harmonic generation(CHG) [2]. So far fundamental wave of a mode-lock
Ti:Sa laser is employed as a seed for the CHG
experiment. In parallel with those experiments, weare considering using high harmonics of the laser as aseed for the CHG experiment and made numericalcalculations and basic experiments.
CHG is a method to produce coherent harmonics oflaser light by using a relativistic electron beam and an
optical klystron type undulator. With increasing
harmonic number of the CHG, the conversion
efficiency rapidly decreases and therefore
short-wavelength coherent light is difficult to obtain.
On the other hand, if higher harmonics of the laser isapplied for the seed, the harmonic number can bemuch reduced and generation of shorter wavelength
coherent light up to soft-X ray region can be expected.
In order to evaluate the effectiveness, we madenumerical calculations. The spectral intensity of CHG
is approximately expressed using the CHG form
factor f n as:

PCHG n | Nf n PSp n ,where N is number of electrons interacted with thelaser and PSp(n) is spectral intensity of incoherent
spontaneous radiation. As CHG spectral intensity is
proportional to the form factor, we estimate efficiencyof the CHG via the form factor. Figure 1 shows
calculated form factor as a function of the harmonic
number of the fundamental laser (not of the seedlaser) under various conditions of the seed laser [3].
Parameters of electron beam from UVSOR-II storage
ring and of the new optical klystron are employed in
the calculation. For 2nd and 4th harmonics generation,
we assume 200 PJ pulse energy and 100 fsec-FWHM
pulse width, which can be provided by harmonic
generation with a nonlinear crystal. For 15th
harmonics of laser, we assume the high harmonic is
produced with Gas and much reduced pulse energy of
5 PJ. As seen in the figure, 2nd and 4-th harmonics oflaser has advantages in producing coherent light inthe VUV and soft X-ray region over fundamental
wave and 15-th harmonics.
We performed experiment to deduced conversion

Fig. 1. Calculated CHG form factor as a function ofharmonic number.
[1] M. Shimada et al., Phys. Rev. Lett. 103 (2009)
144802.
[2] M. Labat et al., Phys. Rev. Lett. 101 (2008)
164803.
[3] N. Wasa, Master’s Thesis, Nagoya University(2012).
[4] S. Sekita, Graduation Thesis, Nagoya University(2012).

33

FEL

Chirality Formation of Amino Acids by Circularly Polarized UV
Irradiation
P. K. Sarker1, J. Takahashi2, Y. Obayashi1, T. Kaneko1, K. Kobayashi1 H. Mita2, J. Takahashi3,K. Matsuo4, M. Hosaka5, M. Adachi6, H. Zen6 and M. Kato6
1

Department of Chemistry and Biotechnology, Faculty of Engineering, Yokohama National University, Yokohama
240-8501, Japan
2
NTT Microsystem Integration Laboratories, Atsugi 243-0198, Japan
3
Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295, Japan
4
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
5
Graduate School of Engineering, Nagoya University, Nagoya 464-8601, Japan
6
Institute for Molecular Science, Okazake 444-8585, Japan

Science obtaining the first evidence ofextraterrestrial amino acids in a carbonaceouschondrite (e.g., Murchison meteorite), a great numberof laboratory experiments have been reported to study
possible abiotic formation of bioorganic compounds
including amino acids and their precursors frompossible astrophysical media by irradiation withhigh-energy particles [1] or ultraviolet (UV) light [2].
It is plausible that considerable number of organic
compounds, including amino acids and theirprecursors, were brought to primitive planets bymicrometeorites (MMs), comets, and interplanetary
dust particles (IDPs). Moreover, amino acids inseveral meteorites (e.g., Murchison, Murray, Orgueil)
have been found to have L-enantiomeric excess, thesame handedness as observed in some biologicalamino acids. Therefore, it has been suggested that lifeon Earth was seeded by the delivery of organic
compounds from outer space during the intense
bombardment period of the primitive Earth [3]. On
the other hand, the origin of homochirality interrestrial biological molecules (dominant L-bodyamino acids and D-body sugars) remains anunresolved important problem in the study for theorigins of life. One of the most attractive hypotheses
for the origin of homochirality is nominated as“Cosmic Scenario”; some chiral impulses fromasymmetric excitation sources in space triggered
asymmetric reactions on the surfaces of such spacematerials as meteorites or interstellar dusts.
According to this scenario, the enantiomeric excesses
in terrestrial amino acids can be advocated thatasymmetric reactions of complex organic molecules
including amino acid precursors were induced bycircularly polarized light (CPL) from synchrotron
radiation (SR) source in space prior to the existenceof terrestrial life. Recently, a wide-field and deepnear-infrared circularly polarized light has been
observed in the Orion nebula, where massive stars
and many low-mass stars are forming [4]. Thisobservation results strongly support the “CosmicScenario” with CPL in space for the origin ofhomochirality in terrestrial bioorganic compounds.
Currently, ground simulation experiments for theextraterrestrial scenario by using CPL from SR

facilities as a simulating polarized energy source isbeing conducted. Aqueous solutions of DL-isovaline(Ival), DL-histidine (His) and DL-5-ethyl5methylhydantoin (EM-Hyd, a precursor of Ival)
were irradiated with UV-CPL at 215 nm from an freeelectron laser source of UVSOR-II (IMS, Japan).
Now, the circular dichroism (CD) spectra of theUV-CPL irradiated compounds are being measured at
the beamline-15 of Hiroshima Synchrotron Radiation
Center (HiSOR, Hiroshima University, Japan).
After UV-LCPL and UV-RCPL irradiation of His,Ival and EM-Hyd, no D- and L-excess was observed(Fig. 1), although very small D- and L-excess wasinvestigatedbyhighperformanceliquidchromatography. As it is very difficult to examine theasymmetricphotodecompositionofUV-CPL
irradiated amino acids in aqueous state, we are now
planning to enlarge their enantiomeric excess (e.e.)which will be investigated in near future.

Fig. 1. CD spectra of non-irradiated and irradiated(UV-CPL) Histidine.
[1] K. Kobayashi et al., Adv. Space Res. 16 (1995)
21.
[2] P. de Marcellus et al., Astrobiology 11 (2011) 847.
[3] J. Bailey, Orig. Life Evol. Biosph. 31 (2001) 167.
[4] T. Fukue et al., Orig. Life Evol. Biosph. 40 (2010)
335.

34