Coherent Synchrotron Radiation Studies and Applications at the NSLS
G. Lawrence Carr
National Synchrotron Light Source
Brookhaven National Laboratory
in collaboration with

D. Arena, Y. Shen, T. Watanabe, R. Lobo, D.B. Tanner, H. Loos, B. Sheehy,
C.-C. Kao, S.L. Kramer, B. Podobedov, J.B. Murphy & X.-J. Wang
NSLS / Brookhaven National Laboratory
operated for U.S. Dep’t of Energy under contract DE-AC02-98CH10886

UVSOR Workshop on Terahertz Coherent Synchrotron Radiation
Inst. for Molecular Science, Nat’l Inst. of Nat. Science, Okazaki, Sept. 23-25, 2007

Outline• Coherent synchrotron radiation from the NSLS VUV/IR storage ring:– Far-infrared spectroscopy at beamline U12IR– CSR bursts in the ~ 100 GHz spectral range.

• Coherent transition radiation from the NSLS Source Development
Laboratory linac:– large THz radiation pulses.
– electro-optic measurement setup to sense waveforms/fields– issues when fields are large (time-dependence)– non-linear optics application:phase modulation to control spectral content, chirping, etc.

• Potential application:– switching behavior in ferroelectrics, ferromagnets, superconductors.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESOutline• Coherent synchrotron radiation from the NSLS VUV/IR storage ring:– Far-infrared spectroscopy at beamline U12IR– CSR bursts in the ~ 100 GHz spectral range.

• Coherent transition radiation from the NSLS Source Development
Laboratory linac:– large THz radiation pulses.
– electro-optic measurement setup to sense waveforms/fields– issues when fields are large (time-dependence)– non-linear optics application:phase modulation to control spectral content, chirping, etc.

• Potential application:– switching behavior in ferroelectrics, ferromagnets, superconductors.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESCoherent Synchrotron Radiation (CSR)• 1st observations in linacs:– Nakazato et al (PRL ‘89), Happek et al (PRL ‘91)

• As a linac bunch diagnostic:– Shibata et al (PRE ‘94), Lai et al (PRE ‘94), Yan et al (PRL ‘00)

• As a THz source– Ishi et al (PRA ‘91), Takahashi et al (RSI ‘98), Carr et al., (Nature ‘02)

• CSR also from storage rings– Arpe et al, Carr et al, Anderson et al, Abo-Bakr et al., ALS, SPRing-8, MIT/Bates, ...

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESNSLS Storage Rings
X-ray ring
2.8 GeV
300ma

VUVIR ring 0.8 GeV1000 ma, 53 MHz RF, 500ps RMS bunch length
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESU12IR - beamline / spectrometerebolometer
Source point

UHV

Mirror M3

cone

chop
window

Mirrors
M1 and M2

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, Japanlamellargrating
interferometer

BROOKHAVEN SCIENCE ASSOCIATESCoherent synchrotron radiation: Beam current dependenceFirst observed: October 1997.
I2 dependence beyond threshold.
threshold depends on operating parameters (E, bunch stretching, α).
–G.L. Carr et al, PAC-99, SPIE: vol. 3775 p.88 (1999),
Nucl. Instrum. & Meth. Phys. Res. A 463, 387 (2001)

1000
2

Detector signal [mV]

•
•
•

S

~I

100

10

S~

I

1
10

100

Beam current [ma]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESVUV Ring Coherent SR: Relative Spectral Intensity

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESCSR Emission Bursts• Quasi-periodic bursts• T ~ 1 to 10 ms• detector-limited fall time

• Risetime < 100 µs for α = αo• increases with decreasing α
4f s =12kHz
Detector Signal [arb.]

Detector Signal [arb.]

20

15

10

5

0
0

20

40

60

80

100

f s = 1kHz

3

2

1

0
0.0

0.5

Time [ms]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, Japan

1.0

1.5

2.0

Time [ms]BROOKHAVEN SCIENCE ASSOCIATESCoherent Bursts: Time Structure (spectrum analysis)

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESOutline• Coherent synchrotron radiation from the NSLS VUV/IR storage ring:– Far-infrared spectroscopy at beamline U12IR– CSR bursts in the ~ 100 GHz spectral range.

• Coherent transition radiation from the NSLS Source Development
Laboratory linac:– large THz radiation pulses.
– electro-optic measurement setup to sense waveforms/fields– issues when fields are large (time-dependence)– non-linear optics application:phase modulation to control spectral content, chirping, etc.

• Potential application:– switching behavior in ferroelectrics, ferromagnets, superconductors.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESThe NSLS Source Development Lab Linac
X.-J. Wang et al

Photocathode gun produces ~ 0.84nC (5x109 electrons) per “shot”~300 fs ~200MeV
electron bunches

dipole chicane
compressor

photocathodee- gunoff-crest
sectionTHz
THz~ 300 fs

~ 4 pschirped~ 4 ps“mono”

266 nm4 ps

800 nm 150 fs pulses~ 150 fs Ti:S oscillator,
amplifier, harmonic gen.


Coherent output to over 1 THz. Potential for shorter bunches with less charge.



Low rep. rate (1 to 10 Hz)
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESTransition Radiation from Relativistic Electrons
Metalelectrons in metal respond totime-varying Coulomb field & radiateθ ~1/γeθ ~1/γrelativistic e beam

note:
radial source size ~ λγ => Rayleigh range ~ λγ2
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, Japane

BROOKHAVEN SCIENCE ASSOCIATESCoherent THz Pulses
e2 ⎡ ⎛ 2 ⎞ ⎤Transition Radiation: Energy per electron per ω → E =⎟⎟ − 1⎥⎢ln⎜⎜
π c ⎣ ⎝1− β ⎠ ⎦1010 electrons, 116 MeV coherent to 1 THz(Happek et al, PRL)=> pulse energy of 400 µJ
Expected behavior
movablemirrorspectra using@ Focus
Far-Field“conventional”
FTIR spectrometer

10electron beamTHzradiationquartz window
pyroelectric pulse
energy detector

Intensity [arb.]

8

6

4

2

Finite source and aperture, quartz windowreflection => ~ 35% efficient or 140 µJ.
We have measured 100 µJ per pulse.

0
0

20

40

60
-1

F r e q u e n c y [c m ]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Characterizion: Electro-Optic Methods
Coherent detection setup for measuring THz waveforms using Pockels Effect: “THz Electro-Optic switch”(Zhang et al, Heinz et al)

E laser ~ cos ⎡⎢ ⎛⎜ 2π n ⎞⎟ z − ω 0 t + ∆ φ E (t )⎤⎥ where ∆φE (t ) = ⎛⎜ 2π L ⎞⎟ ∆n[ETHz (t )]
λ0⎠
λ0 ⎠
⎝
⎣⎝
⎦
Electro-optic material (ZnTe) acts as a “variable waveplate”

THz~300 fs

E-field
signalZnTesampling
pulse

E(t)

polarizer

λ/4polarizing splitterLE (t ) = E (t ) + dE
0

dt

2
d
(t − t ) + ½ E
o

2
(
)
t
−
t
+K
2
o
dt

Result: Detector signal gives instantaneous THz E-field.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Characterizion: Electro-Optic Methods
Coherent detection setup for measuring THz waveforms using Pockels Effect: “THz Electro-Optic switch”(Zhang et al, Heinz et al)

E laser ~ cos [kz + ∆ φ E (t ) − ω t ] where ∆φE (t ) = ⎛⎜ 2π L ⎞⎟ ∆n[ETHz (t )]λ0⎠⎝Electro-optic material (ZnTe) acts as a “variable waveplate”

THz~300 fs

ZnTe
sampling
pulse

E(t)

video camera

λ/4 polarizer

polarizer

L

Result: Snapshot of instantaneous THz E-field.

E (t ) = E (t ) + dE
0

dt

2
d
(t − t ) + ½ E
o

2
(
)
t
−
t
+K
2
o
dt

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESElectro-optic sampling of SDL Linac Coherent THz Pulses
Low charge (intensity) measurement:
Single-cycle at focus: note that Transition Radiation is radially polarized
Jitter (~ 150 fs) limits ability to extract detailed waveforms & spectra.
Need a “single-shot” method
Single shot image of EH

Time slices

80
60

1

20

0
0
-20
-40

-1

-60
-80

-1

0

1

X-Position [mm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESElectric Field (kV/cm)

Y-Position [mm]40Single-Shot Electro-Optic Method
Use chirped sampling laser to encode waveform’s entire time-dependence onto different
wavelengths of laser in a single pulse. Avoids need for multiple sampling.
[Jiang and Zhang, Appl. Phys. Lett. 72, 1945 (1998)].

Elaser ( x, t ) = E0 exp[i (kx − ωt )] = E0 exp[iφ ( x, t )]

ωinst ≡ − ∂φ ( x, t ) ∂t
so, if φ ( x, t ) = kx − ωt − βt 2 then ωinst = ω + βt → linear chirp
Setup for single-shot
EO sensing of
THz waveform

linearpolarizer

ZnTe

THz
chirpedsampling
pulse

Wavelength | Timeλ/4linearpolarizer

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, Japan

spectrometer witharray detector

BROOKHAVEN SCIENCE ASSOCIATESLayout for Characterizing THz Waveforms
aluminum mirror

linac e-beam
motorized
mount

plane
mirrorwire gridpolarizers

THzlaser pulse

Shield wall

plane
mirrorFiber coupledspectrometer

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESSingle-Shot EO Sampling of SDL THz Pulse using Chirped Laser
Time [ps]-3

Intensity [arb.]

1500

-2

-1

0

1

2

3

no THzTHz ONpeak is too high!

2x
1000

1x

500

0
775

780

785

790

795

800

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESSingle-Shot EO Sampling of SDL THz Pulse: Higher intensity
Frequency [THz]
385

380

375

370

Spectral Intensity [arb.]

No THzTHz ON

775

780

785

790

795

800

805

810

815

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Spectral Distribution“New” spectral intensity
appears in the sampling
laser.

-0.8 mm
THz ONreference

Spectral Intensity [arb.]

Now, shift relative timing
between the THz andchirped laser pulse by 0.8mm(places THz nearer to theshort wavelength end of the
chirped laser’s spectrum).

780

785

790

795

800

805

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESTime-Dependent THz E-field and Phase Modulation Effects• Return to details of Pockels electro-optic effect in terms of the induced phase φ[ETHz(t)] for the
sampling laser:

E laser ~ cos [φ0 + φ (t )] ;φ (t ) =2π L

λ0n [ETHz (t )] − ω t• Return to Taylor series expansion (this time for phase):⎡ ⎛ d 2 ETHz
⎞⎤ 2
dE
⎡
⎤
⎛
⎞
THz
− ω⎥ t + ⎢ η ⎜φ (t ) = η E (0) + ⎢ η ⎜⎟2 ⎟⎥ t + K
dt
dt
⎝
⎠
⎣
⎦
⎠⎦
⎣ ⎝
conventional
EO effect

freq.
shift

where η =2 2π L 3
n0 r41λ1+ ε0linearchirp• Different terms in phase correspond to simple phase shifts, spectral shifts and even spectral chirping.
• Result: When THz is sufficiently strong, it modifies the spectral content of the Ti:S laser.

• Note: for 1% wavelength shift at λ=800nm with 0.5mm ZnTe, need dE/dt = 1.3 MV/cm/ps• Application: THz control of ultra-fast laser pulses (tuning, chirp+compression, lensing, …)• Effects simplified using an unchirped laser (to sample just a small segment of THz waveform).
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Characterizion: Electro-Optic Methods“Simple” EO setup to observe time-dependent phase modulation

E laser ~ cos [kz + ∆ φ E (t ) − ω t ] where ∆φE (t ) = ⎛⎜ 2π L ⎞⎟ ∆n[ETHz (t )]λ0⎠⎝Electro-optic material (ZnTe) acts cross phase modulator
ZnTe

THz
sampling
pulse

E(t)

polarizer

L

E (t ) = E (t ) + dE
0

dt

2
d
(t − t ) + ½ E
o

2
(
)
t
−
t
+K
2
o
dt

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESSampling Laser Pulse & Spectral Content
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

370

1.0
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

THz Phase Modulation of Sampling Laser
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
Laser Frequency [THz]φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝
385
380
375

1.0

370

THz
Laser

Spectral Intensity [arb.]

0.5

0.0

-0.5

-1.0
-1

0

Time [ps]

1

770

780

790

800

810

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESCalculated Phase Modulation Effects
2
⎡
⎛
⎞⎤
d
dE
⎤
⎡
⎛
⎞
φ (t ) = η E (0) + ⎢ η ⎜ THz dt ⎟ − ω ⎥ t + ⎢ η ⎜ ETHz 2 ⎟⎥ t 2 + K
dt ⎠⎦
⎠
⎣ ⎝
⎦
⎣ ⎝

Frequency [THz]
380

1.0

375

370

800

810

Laser
spectraTHz

0.5mm thick ZnTe
0.0

Spectral Intensity [arb.]

500 kV/cm field

Laser
0.5

-0.5

E-fields
-1.0
-1

0

1

780

790

Wavelength [nm]Time [ps]Other details: Lensing from spatial variation of n(t) (time-dependent gradient index lens)
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Measured Phase Modulation with SDL Linac Coherent THz•(a) No THz

Electro-optic measurements of SDL THz pulses.
– 35 µJ pulses, 2mm focus, 0.5mm ZnTe.

•~ 130 fs (FWHM) unchirped laser sampling pulse, nopolarization analysis.
Probably still a mixture of effects– optical alignment and waveform distortion– walk-off (velocity mis-match)– phase modulation (2nd and 3rd order NLO)
– dynamic lensing that affects coupling into
spectrometer’s optical fiber.

Vary delay between THz and laser pulse•(b) ∆t=0(c) ∆t=250fs(d) ∆t=500fs(e) ∆t=750fs(f) ∆t=900fs

780

790

800

810

Wavelength (nm)UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESEO Detection of Bunch Coulomb Field (inside linac)
X. Yan et al (PRL ’00)
I. Wilke et al (PRL ’02)
H. Loos et al (PAC ‘03)

Fullcalculation

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESOutline• Coherent synchrotron radiation from the NSLS VUV/IR storage ring:– Far-infrared spectroscopy at beamline U12IR– CSR bursts in the ~ 100 GHz spectral range.

• Coherent transition radiation from the NSLS Source Development
Laboratory linac:– large THz radiation pulses.
– electro-optic measurement setup to sense waveforms/fields– issues when fields are large (time-dependence)– non-linear optics application:phase modulation to control spectral content, chirping, etc.

• Potential application:– switching behavior in ferroelectrics, ferromagnets, superconductors.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESPotential Application: Studies of Magnetization Dynamics
Figure from C. H. Back, et al.,Science 285, 864 (1999)

H
THz• Idea:Use strong THz field to affect magnetization state of a thin film on < 10-12 s time scale.
• Ex situ approach
Use propagating THz wave external to accelerator. Contrast study at SLAC/SPPS (Stöhret al, Nature) where specimen was placed inside linac and directly exposed to electron
beam.
• Method:
pre-saturate film, expose to THz field pulse, then perform post image analysis (SEMPA)• Similar approach could be used for the study of ferroelectric switching.
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESPotential Application: Non-equilibrium Superconductivity
Superconducting state described by complex
order parameter (amplitude and phase).

How does supercurrent (phase) react to a 1
MV/cm, ~ 1ps E-field transient?
Low frequency response is dominated byimaginary part of conductivity.

σ [ω < ωg ] ~ i ω (pure inductor)
dI
L =V
dt

-1

H. Tashiro, D.B. Tanner et al
U. Florida

Conductivity [Ω-cm]

Most time-resolved studies have explored pairbreaking and recombination (amplitude out of
equilibrium) using ω>ωg photons.

α-MoGe film on sapphire

4

1.0x10σ2
3

5.0x10σ1t

1
I (t ) = ∫ V (t ′)dt ′L −∞t

J ≅ σ nω g ∫ E (t ′) d t ′
−∞

0.0
0

10

20

30

40

50

-1

Frequency [cm ]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESTime-dependent Supercurrent in a Thin Film Superconductor
0

10

20

30

Intensity
Electric
Field [V/cm]

1.0 4

5x10

0

0.5
-5x10

-1x10

4

5

-4
-2
0
2
4
0.0
0.0
0.2
0.4
0.6
0.8
1.0

2

1x10

Frequency [cm ]Induced Current Density [A/cm ]

-1

5

1x10

9

5x10

8

JC
0
-4

-2

Time [ps]Frequency [THz]

0

2

4

Time [ps]Note: a typical superconductor has critical current JC ~ 108 A/cm2=> “over twist” the local superconducting phase, spin off vortices?
How quickly can a vortex be created? How does dissipation initially appear?
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESSummary• Coherent SR bursts from NSLS VUV/IR ring
• Intense CTR pulses from photo-injected linac– single-cycle pulses– large electro-optic effects: time-dependence leads to laser phase modulation• spectral shifting & chirping• could be used to control ultrafast laser pulses.
• affects in situ EO sampling of thee-beam Coulomb field.

• Large pulse energy −> strong electric (& magnetic) fields.
– opportunity for studying field-induced ultra-fast switching.
– initially: “photographic” samples– or waveform distortion in transmitted THz pulse.
– ultimately: THz, other probe (x-rays, electrons)

Acknowledgements: J. Misewich, G. Nintzel, R. Smith, B. Singh (Brookhaven),
T.F. Heinz (Columbia), Dave Reitze (Florida)
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

end of slide show
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UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESSingle-Shot EO Sampling of SDL THz Pulse: Higher intensity
Frequency [THz]
385

380

375

370

Spectral Intensity [arb.]

No THzTHz ON

775

780

785

790

795

800

805

810

815

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESFull Electro-Optic Calculation
Frequency [THz]
385

380

375

370

Spectral Intensity [arb.]

No THz250 kV/cm

775

780

785

790

795

800

805

810

815

Wavelength [nm]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Fields for Relativistic Electron
Non-relativistic Coulomb Field

Relativistic
Relativistic (3(1 MeV)
GeV) Coulomb Field

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Radiation from Electron on Circular Orbit
Relativistic parameters

β=v

c

γ =

1
1− β 2m = m0γ
Modern accelerators:
β ~ 0.99999999
γ ~ 6000β ~ 0.95

Calculated using
Radiation2D code
Tsumoru Shintake

RIKEN / Spring-8

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESTransition Radiation: Coulomb Field & Spectral Content
Radial Source Size (“waist”): W ~ λγ /2πTime-dependent Coulomb field

Spectral Content (not to scale)UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Short Bunch Source: The NSLS Source Development Lab Photo-injected Linac
BNL
Photo-injector IV

300 MeV
S-Band Linac(DARPA)

10 m NISUS Wiggler (SDI)

Chicane Bunch Compressor

Ti:Sapphire Laser

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESMaking Short Bunches• Problem: Electron charge Î Coulomb repulsion– Coulomb interaction causes spread in the energy distribution of a bunch.
– For a non-relativistic electron, energy spread => velocity spread => distance spread.
– BUT: For highly relativistic electrons, velocity spread remains small (mass varies).
=> Start with long bunch, accelerate to high energy, then compress.

RF Linac voltage (-)

Compression method analogous to light, magnets serve as dispersive optics for electrons.
Direction of travelon crest (standard)off crest (energy chirp)
Dipole chicane to compress chirped bunch
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Statistics• Shot-to-shot fluctuations affect120

usefulness of pulses for some
applications.

– Pump-probe spectroscopy• Typical fluctuations 4 to 6% RMS.

Number– Interferometry

100

1000 pulses
500 pC80

34 µJ avg.
σ = 5.6%60

40– due mostly to variations incharge (particle number)from laser fluctuations.

20• High rep. rate (average) or single-

0

shot capability needed.

0

10

20

30

40

Pulse Energy [µJ]UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

N2 dependence• Intensity ~ Q2 (∝ N2) is asignature of coherent emission.

Detected Power [arb.]

1000

100

e
op
l
S

10

=

2

1

10

Charge [pC]
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESOpportunities in Magnetism with THz Pulses
Ultra-Short Pulses and/or High Fields -- D. Arena / NSLS
Current state of the art for “ultra-fast” dynamics experiments:THzmvi agnsc eos tic
ity

pr
sp
ec
St exc
in
e
s
-la
on ha
sp
an pinan ssio
er ng
t
i
(
i
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t
n
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l
m ice ow w
ex e
sp coh d d nal
an re
av
am ro
ci int
in er
q
ta
e
g
e
l
l
e
t
di n
an ax im s
tio rac
ffu ce ping atioai
ite tit
ns tionsios on )nn

Time: ~100 fs (lasers)~100 ps (synchrotron)
Field: ~10 – 100 gauss (stripline)

Excitation / Interaction
10-15
105

103

102

field
(gauss)10-12 104

10-9

10-6 101

time
(sec)

Coercivity / Saturation
.
oy
N2
nd
h
6
s
n
o
all
t
1
s
e
r
o y
e c
rm
iti allo soft nite ilut emi
ea ets ″ F
e
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p
e
n &
d cs
ga
ar agn ainr
traals
t
a
m
m
ne
et
g
a
m
m

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESTime (s)THz Driven Magnetic Dynamics

10-6

Use ultra-short magnetic field pulses to
induce spin excitations (D. Arena / NSLS)
DomainPropagation
H

10-9

10-12

10-15

Spin-Lattice
Relaxation

Spin
Precession

Spin-Orbital
Exchangee-Excitation / Interaction
Exchange interaction
Stoner excitations
Spin waves
Spin – lattice relaxation

Timescale (sec)
10-15
10-15 - 10-14
10-12 (low q limit)
10-12 - 10-11 (in manganites)

Precessional motion
Spin injection
Spin diffusion

10-10 - 10-9
TBD
TBD

Spin coherence

TBD

e-

Co
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATESElectro-Optic Details for ZnTe
S. Casalbuoni, H. Schlarb, B. Schmidt, P. Schmüser,B. Steffen, A. Winter DESY & Universität Hamburg“Numerical Studies on the Electro-Optic Sampling ofRelativistic Electron Bunches” (TESLA Report 2005-01)

α = 0 −> ψ = π/4 (45°)∆φ (E ) =

2π L

λ0

(n1 − n2 ) = 2π L ∆n(E )λ0

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Multi-particle Coherent Synchrotron Radiation (CSR)
Accelerators typically have many electrons traveling in a “bunch”. Can emission be coherent?
Yes -- if bunch (or some portion of it) has length that is short compared to wavelength.

S(r)bunch density

λ << lb
E~ N1/2; I ~ Nλ >> lb;r

E ~ N; I ~ N2

dI (ω )dI (ω )= [N + N (N − 1) f (ω )]d ω multiparti cledω∞where f (ω ) = ∫ e−∞riω nˆ ⋅ r / c

S (r )dr~ N2

2(Nodvick & Saxon)

In some accelerators, bunch lengths are 100s of fs (=>THz), and N can be large e.g. ~ 1010
UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES

Threshold dependence on fs0
s0

Keil-Schnell(coasting / unbunched beam)eI aveZnn≤ 2παEσ E2

I th ∝ α ~ f s20
Boussard
replace Iave with Ipeak

I th ∝ α 3 / 2 ~ f s30

UVSOR Workshop on THz Coherent Synchrotron Radiation
23-25 September 2007, IMS Okazaki, JapanBROOKHAVEN SCIENCE ASSOCIATES