Coherent Synchrotron Radiation Studies and Applications at the NSLS - - PowerPoint PPT Presentation

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Coherent Synchrotron Radiation Studies and Applications at the NSLS - - PowerPoint PPT Presentation

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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.

slide-1
SLIDE 1

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

  • perated 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
slide-2
SLIDE 2

BROOKHAVEN SCIENCE ASSOCIATES

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

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.

slide-3
SLIDE 3

BROOKHAVEN SCIENCE ASSOCIATES

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

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.

slide-4
SLIDE 4

BROOKHAVEN SCIENCE ASSOCIATES

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

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, ...

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SLIDE 5

BROOKHAVEN SCIENCE ASSOCIATES

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

NSLS Storage Rings

X-ray ring 2.8 GeV 300ma VUVIR ring 0.8 GeV 1000 ma, 53 MHz RF, 500ps RMS bunch length

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SLIDE 6

BROOKHAVEN SCIENCE ASSOCIATES

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

U12IR - beamline / spectrometer

Mirror M3 Mirrors M1 and M2 Source point

e UHV

window cone

bolometer lamellar grating interferometer

chop

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SLIDE 7

BROOKHAVEN SCIENCE ASSOCIATES

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

Coherent synchrotron radiation: Beam current dependence

  • First 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)

10 100 1 10 100 1000 S ~ I S ~ I

2

Detector signal [mV] Beam current [ma]

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SLIDE 8

BROOKHAVEN SCIENCE ASSOCIATES

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

VUV Ring Coherent SR: Relative Spectral Intensity

slide-9
SLIDE 9

BROOKHAVEN SCIENCE ASSOCIATES

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

CSR Emission Bursts

0.0 0.5 1.0 1.5 2.0 1 2 3 4

fs=12kHz fs= 1kHz Detector Signal [arb.] Time [ms]

20 40 60 80 100 5 10 15 20

Detector Signal [arb.] Time [ms]

  • Quasi-periodic bursts
  • T ~ 1 to 10 ms
  • detector-limited fall time
  • Risetime < 100 µs for α = αo
  • increases with decreasing α
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SLIDE 10

BROOKHAVEN SCIENCE ASSOCIATES

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

Coherent Bursts: Time Structure (spectrum analysis)

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SLIDE 11

BROOKHAVEN SCIENCE ASSOCIATES

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

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.

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SLIDE 12

BROOKHAVEN SCIENCE ASSOCIATES

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

The NSLS Source Development Lab Linac

Coherent output to over 1 THz. Potential for shorter bunches with less charge. Low rep. rate (1 to 10 Hz)

photocathode e- gun dipole chicane compressor ~ 300 fs ~ 200MeV electron bunches

THz THz

~ 150 fs Ti:S oscillator, amplifier, harmonic gen. 800 nm 150 fs pulses 266 nm 4 ps

~ 4 ps “mono” ~ 4 ps chirped

  • ff-crest

section ~ 300 fs

Photocathode gun produces ~ 0.84nC (5x109 electrons) per “shot”

X.-J. Wang et al

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SLIDE 13

BROOKHAVEN SCIENCE ASSOCIATES

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

Transition Radiation from Relativistic Electrons

θ ~1/γ θ ~1/γ Metal

e e

electrons in metal respond to time-varying Coulomb field & radiate note: radial source size ~ λγ => Rayleigh range ~ λγ2 relativistic e beam

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SLIDE 14

BROOKHAVEN SCIENCE ASSOCIATES

UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan 2 0 4 0 6 0 2 4 6 8 1 0

Intensity [arb.] F re q u e n c y [c m

  • 1]

spectra using “conventional” FTIR spectrometer

Far-Field

Expected behavior

@ Focus

Coherent THz Pulses

Transition Radiation: Energy per electron per ω →

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = 1 1 2 ln

2

β π c e E

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

movable mirror pyroelectric pulse energy detector quartz window electron beam THz radiation

1010 electrons, 116 MeV coherent to 1 THz => pulse energy of 400 µJ

(Happek et al, PRL)

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SLIDE 15

BROOKHAVEN SCIENCE ASSOCIATES

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

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)

( ) ( ) ( ) ( )

K + − + − + =

2 2 2

½

  • t

t dt E d t t dt dE t E t E

λ/4

polarizer polarizing splitter

sampling pulse ZnTe

THz

E(t)

~300 fs

E-field signal

Result: Detector signal gives instantaneous THz E-field.

Electro-optic material (ZnTe) acts as a “variable waveplate”

L

( )⎥

⎦ ⎤ ⎢ ⎣ ⎡ ∆ + − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ t t z n E

E laser

φ ω λ π 2 cos ~

( ) ( ) [ ]

t E n L t

THz E

∆ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ∆ 2 λ π φ

where

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SLIDE 16

BROOKHAVEN SCIENCE ASSOCIATES

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

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)

( ) ( ) ( ) ( )

K + − + − + =

2 2 2

½

  • t

t dt E d t t dt dE t E t E

λ/4

polarizer polarizer

sampling pulse ZnTe

THz

E(t)

~300 fs Result: Snapshot of instantaneous THz E-field.

Electro-optic material (ZnTe) acts as a “variable waveplate”

L

video camera

( ) [ ]

t t kz E

E laser

ω φ − ∆ + cos ~

( ) ( ) [ ]

t E n L t

THz E

∆ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ∆ 2 λ π φ

where

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SLIDE 17

BROOKHAVEN SCIENCE ASSOCIATES

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

Electro-optic sampling of SDL Linac Coherent THz Pulses

  • 1

1

  • 1

1

Y-Position [mm] X-Position [mm]

Electric Field (kV/cm)

  • 80
  • 60
  • 40
  • 20

20 40 60 80

Single shot image of EH

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

Time slices

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SLIDE 18

BROOKHAVEN SCIENCE ASSOCIATES

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

Single-Shot Electro-Optic Method

linear polarizer spectrometer with array detector

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)].

linear polarizer

λ/4 Setup for single-shot EO sensing of THz waveform

chirped sampling pulse

ZnTe THz

Wavelength | Time

( ) [ ] [ ]

) , ( exp exp ) , ( t x i E t kx i E t x Elaser φ ω = − = t t x

inst

∂ ∂ − ≡ ) , ( φ ω

2

) , ( t t kx t x β ω φ − − =

→ linear chirp

t

inst

β ω ω + =

so, if then

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SLIDE 19

BROOKHAVEN SCIENCE ASSOCIATES

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

Layout for Characterizing THz Waveforms

aluminum mirror Fiber coupled spectrometer

Shield wall linac e-beam

THz

motorized mount plane mirror plane mirror wire grid polarizers

laser pulse

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SLIDE 20

BROOKHAVEN SCIENCE ASSOCIATES

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

Single-Shot EO Sampling of SDL THz Pulse using Chirped Laser

775 780 785 790 795 800 500 1000 1500

no THz Intensity [arb.] Wavelength [nm]

  • 3
  • 2
  • 1

1 2 3

Time [ps]

775 780 785 790 795 800 500 1000 1500

no THz THz ON Intensity [arb.] Wavelength [nm]

  • 3
  • 2
  • 1

1 2 3

Time [ps]

peak is too high!

1x 2x

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SLIDE 21

BROOKHAVEN SCIENCE ASSOCIATES

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

Single-Shot EO Sampling of SDL THz Pulse: Higher intensity

385 380 375 370

Frequency [THz] Spectral Intensity [arb.]

775 780 785 790 795 800 805 810 815

No THz THz ON Wavelength [nm]

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SLIDE 22

BROOKHAVEN SCIENCE ASSOCIATES

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

Spectral Distribution

780 785 790 795 800 805

  • 0.8 mm

THz ON reference

Spectral Intensity [arb.]

Wavelength [nm]

Now, shift relative timing between the THz and chirped laser pulse by 0.8mm (places THz nearer to the short wavelength end of the chirped laser’s spectrum). “New” spectral intensity appears in the sampling laser.

slide-23
SLIDE 23

BROOKHAVEN SCIENCE ASSOCIATES

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

( ) [ ];

cos ~ t Elaser φ φ +

( ) [ ]

t t E n L t

THz

ω λ π φ − = 2 ) (

  • Return to details of Pockels electro-optic effect in terms of the induced phase φ[ETHz(t)] for the

sampling laser:

  • 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).

Time-Dependent THz E-field and Phase Modulation Effects

conventional EO effect freq. shift

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

linear chirp

41 3

2 1 2 r n L λ π ε η + =

where

  • Return to Taylor series expansion (this time for phase):
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SLIDE 24

BROOKHAVEN SCIENCE ASSOCIATES

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

THz Characterizion: Electro-Optic Methods

“Simple” EO setup to observe time-dependent phase modulation

( ) ( ) ( ) ( )

K + − + − + =

2 2 2

½

  • t

t dt E d t t dt dE t E t E

polarizer

sampling pulse ZnTe

THz

E(t)

Electro-optic material (ZnTe) acts cross phase modulator

L

( ) [ ]

t t kz E

E laser

ω φ − ∆ + cos ~

( ) ( ) [ ]

t E n L t

THz E

∆ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ∆ 2 λ π φ

where

slide-25
SLIDE 25

BROOKHAVEN SCIENCE ASSOCIATES

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

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 Laser

Time [ps]

Sampling Laser Pulse & Spectral Content

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-26
SLIDE 26

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-27
SLIDE 27

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-28
SLIDE 28

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-29
SLIDE 29

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-30
SLIDE 30

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-31
SLIDE 31

BROOKHAVEN SCIENCE ASSOCIATES

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

385 380 375 370

Laser Frequency [THz] Spectral Intensity [arb.]

770 780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0 THz Laser

Time [ps]

THz Phase Modulation of Sampling Laser

( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-32
SLIDE 32

BROOKHAVEN SCIENCE ASSOCIATES

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

Calculated Phase Modulation Effects

Other details: Lensing from spatial variation of n(t) (time-dependent gradient index lens) 500 kV/cm field 0.5mm thick ZnTe

380 375 370

Frequency [THz] Spectral Intensity [arb.]

780 790 800 810

Wavelength [nm]

  • 1

1

  • 1.0
  • 0.5

0.0 0.5 1.0

THz Laser Time [ps]

E-fields

Laser spectra ( )

K + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + =

2 2 2

) ( t dt E d t dt dE E t

THz THz

η ω η η φ

slide-33
SLIDE 33

BROOKHAVEN SCIENCE ASSOCIATES

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

(a) No THz (c) ∆t=250fs (d) ∆t=500fs (e) ∆t=750fs (f) ∆t=900fs (b) ∆t=0

790 800 780 810

Wavelength (nm)

Measured Phase Modulation with SDL Linac Coherent THz

  • Electro-optic measurements of SDL THz pulses.

– 35 µJ pulses, 2mm focus, 0.5mm ZnTe.

  • ~ 130 fs (FWHM) unchirped laser sampling pulse, no

polarization analysis.

  • Probably still a mixture of effects

–

  • ptical 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

slide-34
SLIDE 34

BROOKHAVEN SCIENCE ASSOCIATES

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

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)

Full calculation

slide-35
SLIDE 35

BROOKHAVEN SCIENCE ASSOCIATES

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

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.

slide-36
SLIDE 36

BROOKHAVEN SCIENCE ASSOCIATES

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

  • 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 (Stöhr et 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.

Potential Application: Studies of Magnetization Dynamics

H THz

Figure from C. H. Back, et al., Science 285, 864 (1999)

slide-37
SLIDE 37

BROOKHAVEN SCIENCE ASSOCIATES

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

Potential Application: Non-equilibrium Superconductivity

10 20 30 40 50 0.0 5.0x10

3

1.0x10

4

Conductivity [Ω-cm]

  • 1

Frequency [cm

  • 1]

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

α-MoGe film on sapphire

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

σ2 σ1

( ) t

d t E J

t g n

′ ′ ≅

∫

∞ −

ω σ

V dt dI L =

( ) ( )

∫

∞ −

′ ′ =

t

t d t V L t I 1

[ ]

ω ω ω σ i

g ~

<

(pure inductor) Superconducting state described by complex

  • rder parameter (amplitude and phase).

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

slide-38
SLIDE 38

BROOKHAVEN SCIENCE ASSOCIATES

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

Time-dependent Supercurrent in a Thin Film Superconductor

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.5 1.0

Intensity Frequency [THz]

10 20 30

Frequency [cm

  • 1]
  • 4
  • 2

2 4

  • 1x10

5

  • 5x10

4

5x10

4

1x10

5

Electric Field [V/cm] Time [ps]

  • 4
  • 2

2 4 5x10

8

1x10

9

Induced Current Density [A/cm

2]

Time [ps]

=> “over twist” the local superconducting phase, spin off vortices? How quickly can a vortex be created? How does dissipation initially appear? Note: a typical superconductor has critical current JC ~ 108 A/cm2

JC

slide-39
SLIDE 39

BROOKHAVEN SCIENCE ASSOCIATES

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

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)

slide-40
SLIDE 40

BROOKHAVEN SCIENCE ASSOCIATES

UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan end of slide show please applaud now

slide-41
SLIDE 41

BROOKHAVEN SCIENCE ASSOCIATES

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

Single-Shot EO Sampling of SDL THz Pulse: Higher intensity

385 380 375 370

Frequency [THz] Spectral Intensity [arb.]

775 780 785 790 795 800 805 810 815

No THz THz ON Wavelength [nm]

slide-42
SLIDE 42

BROOKHAVEN SCIENCE ASSOCIATES

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

Full Electro-Optic Calculation

385 380 375 370

No THz 250 kV/cm Frequency [THz] Spectral Intensity [arb.]

775 780 785 790 795 800 805 810 815

Wavelength [nm]

slide-43
SLIDE 43

BROOKHAVEN SCIENCE ASSOCIATES

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

Fields for Relativistic Electron

Relativistic (3 MeV) Coulomb Field Non-relativistic Coulomb Field Relativistic (1 GeV) Coulomb Field

slide-44
SLIDE 44

BROOKHAVEN SCIENCE ASSOCIATES

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

Radiation from Electron on Circular Orbit

Calculated using Radiation2D code Tsumoru Shintake RIKEN / Spring-8

c v = β

2

1 1 β γ − =

γ m m =

Relativistic parameters

Modern accelerators: β ~ 0.99999999 γ ~ 6000 β ~ 0.95

slide-45
SLIDE 45

BROOKHAVEN SCIENCE ASSOCIATES

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

Transition Radiation: Coulomb Field & Spectral Content

Time-dependent Coulomb field Spectral Content (not to scale)

Radial Source Size (“waist”): W ~ λγ λγ /2π

slide-46
SLIDE 46

BROOKHAVEN SCIENCE ASSOCIATES

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

10 m NISUS Wiggler (SDI) 10 m NISUS Wiggler (SDI)

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

300 MeV 300 MeV S S-

  • Band Linac

Band Linac (DARPA) (DARPA) Ti:Sapphire Ti:Sapphire Laser Laser BNL BNL Photo Photo-

  • injector IV

injector IV

Chicane Bunch Compressor Chicane Bunch Compressor

slide-47
SLIDE 47

BROOKHAVEN SCIENCE ASSOCIATES

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

Making Short Bunches

  • Problem: Electron charge 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 (-) Direction of travel

  • n crest (standard)
  • ff crest (energy chirp)

Compression method analogous to light, magnets serve as dispersive optics for electrons.

Dipole chicane to compress chirped bunch

slide-48
SLIDE 48

BROOKHAVEN SCIENCE ASSOCIATES

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

Statistics

  • Shot-to-shot fluctuations affect

usefulness of pulses for some applications.

– Interferometry – Pump-probe spectroscopy

  • Typical fluctuations 4 to 6% RMS.

– due mostly to variations in

charge (particle number) from laser fluctuations.

  • High rep. rate (average) or single-

shot capability needed.

10 20 30 40 20 40 60 80 100 120

1000 pulses 500 pC 34 µJ avg.

σ = 5.6%

Number Pulse Energy [µJ]

slide-49
SLIDE 49

BROOKHAVEN SCIENCE ASSOCIATES

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

N2 dependence

  • Intensity ~ Q2 (∝ N2) is a

signature of coherent emission.

1 10 10 100 1000

Slope = 2

Detected Power [arb.] Charge [pC]

slide-50
SLIDE 50

BROOKHAVEN SCIENCE ASSOCIATES

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

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:

THz

magnetic viscosity field (gauss)

10-15 10-12 10-9 10-6

Excitation / I nteraction

exchange interaction Stoner excitations spin waves (low q limit) spin-lattice relaxation in manganites precessional rotation and damping spin coherence and spin diffusion

Coercivity / Saturation

time (sec)

105 104 101 102 103

soft manganites permalloy transition metals & alloys a″ Fe16N2 dilute magnetic semicond. rare-earth magnets

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

slide-51
SLIDE 51

BROOKHAVEN SCIENCE ASSOCIATES

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

Co Time (s) Spin Precession Spin-Lattice Relaxation Domain Propagation

10-15 10-12 10-9 10-6 e- e-

H Spin-Orbital Exchange

THz Driven Magnetic Dynamics

10-10 - 10-9 Precessional motion TBD Spin coherence TBD Spin diffusion TBD Spin injection 10-12 - 10-11 (in manganites) Spin – lattice relaxation 10-12 (low q limit) Spin waves 10-15 - 10-14 Stoner excitations 10-15 Exchange interaction Timescale (sec) Excitation / Interaction

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

slide-52
SLIDE 52

BROOKHAVEN SCIENCE ASSOCIATES

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

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 of Relativistic Electron Bunches” (TESLA Report 2005-01)

α = 0 −> ψ = π/4 (45°)

( ) ( ) ( )

E n L n n L E ∆ = − = ∆

2 1

2 2 λ π λ π φ

slide-53
SLIDE 53

BROOKHAVEN SCIENCE ASSOCIATES

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

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) r bunch density λ << lb E~ N1/2; I ~ N λ >> lb; E ~ N; I ~ N2 ( ) ( ) ( ) [ ] ( )

ω ω ω ω ω d dI f N N N d dI

cle multiparti

1 − + =

( ) ( )

2 / ˆ

∫

∞ ∞ − ⋅

= dr r S e f

c r n i r ω

ω

where (Nodvick & Saxon)

In some accelerators, bunch lengths are 100s of fs (=>THz), and N can be large e.g. ~ 1010

2

~ N

slide-54
SLIDE 54

BROOKHAVEN SCIENCE ASSOCIATES

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

Threshold dependence on fs0 Threshold dependence on fs0

2

2

E n ave

E n Z eI σ πα ≤

2

~

s th

f I α ∝ Keil-Schnell

(coasting / unbunched beam)

Boussard

replace Iave with Ipeak

3 2 / 3

~

s th

f I α ∝