Download - Frequency-domain interferometry diagnostic system for the detection of relativistic plasma waves
UCLA
LIGO-G030514-00-Z
Frequency-domain interferometry diagnostic systemfor the detection of relativistic plasma waves
Catalin V. Filip, Electrical Engineering Department, UCLA
UCLA
LIGO-G030514-00-Z
IntroductionRelativistic Plasma Waves Can Accelerate Electrons
• Relativistic Plasma Waves have phase velocities, vphase c
• Externally injected electrons can “surf” these waves and get accelerated with gradients of few GeV/m
(100 – 1000 times more than conventional accelerators)
• Plasma accelerators could be << in size than conventional accelerators (and therefore much cheaper)
• Relativistic Plasma Waves can be excited by the beat pattern of an intense, two-wavelength laser pulse
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LIGO-G030514-00-Z
IntroductionRelativistic Plasma Waves Can Accelerate Electrons
Laser
Longitudinal
Electric FieldOf the wave QuickTime™ and a
Animation decompressorare needed to see this picture.
Horizontal (mm)
Ver
tica
l (m
m)
Longit
udin
al e
lect
ric
fiel
d (
MV
/cm
)
0
-20
20
1 2 30
100µm
focus
(a)
(b)
Laser Pulse
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LIGO-G030514-00-Z
Relativistic Plasma Waves (RPWs)Detection Techniques
There are TWO major ways to detect a RPW
1 electrons accelerated electrons
PLASMAWAVE
1. by probing the RPW with electrons(the electric field of the wave is inferred)PLASMA
PLASMAWAVE
2
kprobe
kprobe
kscatter
scatter= probe epw
kscatter= kprobe kepw
2. by probing the RPW with light (photons)(the absolute density perturbation n is inferred)
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LIGO-G030514-00-Z
Detection of Relativistic Plasma Waves-Collinear Thomson Scattering
background plasma
532-nm probe beam duringand after interaction with the plasma wave
probe beam gets modulated in phase (and amplitude)
= index of refractionin a plasma:
= 1- nncrit
< 1
For a 532-nm light wave going
through a plasma a change inplasma density of
n=1014 cm-3
(1% wave at 1016 cm-3)is equivalent to a change inthe index of refraction of
10-8
UCLA
LIGO-G030514-00-Z
Detection of Relativistic Plasma Waves-Collinear Thomson Scattering
Amplitude modulation is
10-8 - 10-10
period = 1 ps
= 1 THz
~16 Å
for a plasma density of 1016 cm-3
Scattered light
P0
Ps ~ [ n (cm-3) x probe x Linter ]2
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LIGO-G030514-00-Z
Relativistic Plasma Waves (RPW) Detectionat UCLA - Goals
1. Detection of the longitudinal component of RPW2. Detection of RPW at low densities (1015 cm-3 to 1017 cm-3)3. Good signal-to-noise ratio (1000 to 1)4. Frequency and time-resolved (both red and blue shift)5. Use of independent probe to avoid stray scattering6. Easy to implement, reliable, on-line with electrons
UCLA
LIGO-G030514-00-Z
Experimental challenges
1. Scattering lasts for ~100 ps => MUST use streak camera => MUST
use visible pulses for probing => Very small scattering efficiency
Pscattered/Pprobe 10-8 - 10-10 => MUST use MW-power probe laser pulses
with duration ≥ 2ns for easy synchronization => Pulse energy is high =>
MUST use high-damage threshold optics
2. The VERY WEAK scattered light is only ~8 Å away from the
VERY INTENSE probe light
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LIGO-G030514-00-Z
Experimental considerations
frequencyor wavelength
probe lightamplitude =109
scattered lightamplitude =1
8 Å 8 Å
Etalontransmission
1. First use a “power” filter to decrease the power of the probe pulse (~1000 times) in order to use a grating afterwards
2. Use an etalon with high-damage threshold coatings as a “power” filter.
532nm = 3.51015 Hz
~1012 Hz3. Hope that the bandwidth of the probe laser pulse is narrow enough.
UCLA
LIGO-G030514-00-Z
Experimental Setup For Frequency And TimeResolved Collinear Thomson Scattering
ImagingSpectrometer
Input
Output
StreakCamera
27 reflecting surfaces,9 lenses, 5 focii
Beam Dump
Etalon (high-power filter)
100 ps CO2 pulse drivesplasma wave
F# = 2, Imax=1015 W/cm2
DCR-11Nd:YAG
Q-Switched532.1 nm
100 mJ, 5 ns
Interaction Chamber
OAP
20 MW
Beam dumpfor 532.1 nm
10 kW
< 2 mW
To positionmonitor
Grating (low-power)filter
Beam rotator
Teflondump Mirror
Mirror
Spatial filter
IP
f=1 m
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LIGO-G030514-00-Z
+ - Spectrometer
16-bit CCDWhite-light source
Spatial filterand collimator
Etalon
Spectrometerslit
a
b c
0
1000
2000
3000
4000
528 529 530 531 532 533 534 535 536
Wavelength (nm)
Inte
nsit
y (c
ount
s)
Etalon preliminary test and measurements
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LIGO-G030514-00-Z
QuickTime™ and aTIFF decompressor
are needed to see this picture.
QuickTime™ and aTIFF decompressor
are needed to see this picture.
Gree-Ne (543nm) beam
Etalon preliminary test and measurements
532nm, 100 mJ
Energy meter
Energy meter
Profile of the reflection of the543 nm Gaussian He-Ne gas laser beam
Camera
Camera
Attenuation of the probe pulse at 532.1 nm is only ~10 times!
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LIGO-G030514-00-Z
Multi-passing of the Etalon
50 µm
1
2 BeamDump
3
10%
1%0.1%
To grating
Multi-passing of the etalon is achieved by sending theprobe beam on consequent transmission maxima.
Top view
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LIGO-G030514-00-Z
Grating preliminary test and measurements
0th order
Ist orderMonitor
Signal
Razor blade on atranslation stage
The grating can reduce theprobe light ~107 times withoutattenuating the scattered light
532nm~5 mJ
Beam splitter
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LIGO-G030514-00-Z
0
10
20
30
40
531 532 533 534
Ne lines
Wavelength (nm)
Rel
ativ
e T
rans
mis
sion
531 533 535
0.0
2.5
5.0
7.5
50 150 250
Dis
tanc
e (m
m)
Ne lines
Wavelength (nm)
Intensity (counts)
(a)(b)
White light measurements
Etalonattenuation
at probe
Signal at probe+8Å
Signal at probe– 8Å
UCLA
LIGO-G030514-00-Z
1. Plasma is produced by tunneling ionization of backfill gas- H2, He, Ar from 1015 cm-3 to 1017 cm-3
2. CO2 laser parameters:- ≤100 ps FWHM, 2-, 10.3µm and 10.6 µm- energy, 10.6/10.360J/25J, maximum 1 TW- beam size (dia.) from 1.5” to 3.4”,- OAP focussing down to 2 w0 120 µm- max. 6 1015 W/cm2, linearly polarized
3. Probe pulse parameters:- visible, Q-switched, Nd:YAG, 532.1 nm- ~100 mJ in 5 ns, 1011 W/cm2 in plasma
4. Thomson scattering parameters- collinear (0 degree) geometry, and k-matched for relativistic plasma waves- interaction length ~2 zR 2 mm
- frequency resolution 0.4 Å, time resolution ~100 ps (grating limited)
Experimental Parameters
CO2
probe
Plasma
Probebeam
CO2 laserbeam
Plasma
3mm
35mm
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LIGO-G030514-00-Z
250 750 1250
531.0
531.5
532.0
532.5
533.0
125 250 375 500 625 750
200 900 1600 2300
530.00
531.25
532.50
533.75
535.00
20 90 160 230 300
11341,322 mTorr He 11358,1.73 Torr He
Blue shifted sidebands (in He)
Red shifted sidebands
10 x attn.
Time-Resolved Spectra FromCollinear Thomson Scattering
n = 1.07 nres n = 5.76 nres
Wav
elen
gth
Wav
elen
gth
Time (ps)
Line of Simultaneous
events
C. V. Filip et al., Rev. Sci. Instr. 74, 3576 (2003)also in July 2003 Virtual Journal of Ultrafast Science, http://www.vjultrafast.org.
UCLA
LIGO-G030514-00-Z
160 ps
1500 2000 2500
532.0
532.5
533.0
533.5
534.0
534.5
535.0
40 50 60 70 80 900
0
100
200
300
400
500
400 600 800 1000 1200 1400
Time (ps)
Inte
nsi
ty (
cou
nts
)
Lineout of the red shifted2nd harmonic beatwave component
10x attn.
Beatwave
Time (ps)
Intensity (arb. units)
Wav
elen
gth
(n
m)
2nd harmonic
3rd harmonic
Probe pulseat 532.1 nm
2Torr H2; n=13.3 nres
Ratio of intensityof 1st/2nd harmonic
R 20
Relativistic Plasma Wave Detection in H2
Off Resonance
CO2 pulse ~ 100 ps
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c Æ
d
~ 3 cm
~ 3
cm
Incoming pulse
Outgoing pulse in I-st order of grating
Temporal resolution of thediagnostic system 100 ps
∆d=
i
DNprobe
cCos(i)
D
100ps
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LIGO-G030514-00-Z
Time Resolved Spectra FromF/18 Collinear Thomson Scattering, n=nres
0.0 3.0 6.0 9.0 12.0
532.0
533.0
534.0
Time (ns)
Wav
elen
gth
(nm
)
133 227 320 413 507 600Intensity (counts)
0.00 3.00 6.00 9.00 12.000
175
350
525
700
0
175
350
525
700
Time (ns)
Int.
(cou
nts)
PROBE
-
100x
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Acceleration of injected electrons in H2
at n=3.3nres
10
100
1000
104
105
106
107
108
109
15 20 25
Ele
ctro
ns/M
eV
Energy (MeV)
Noise level
12 13 14 15Energy (MeV)
12 MeV,injectionenergy
3
Single frequency
Shot #11999
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LIGO-G030514-00-Z
Conclusions
A Thomson scattering diagnostic system has been used to detectrelativistic plasma waves excited at low plasma densities (0.1% critical).
The probing was done collinearly with an independent probe laser pulse.
A novel spatial-spectral notch filter based on a triple-pass Fabry-Perot etalonwas utilized to simultaneously attenuate the probe light ~1012 times
and collect the weak, 100-ps scattered light which is shifted by only ~8 Å.
Both the red and blue-shifted scattered light up to the third harmonicwas recorded in time and frequency. Using this system, non-resonantly
excited plasma waves were characterized.