laser driven accelerators for a new frontier in ultrafast physics...laser driven accelerators for a...
TRANSCRIPT
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Laser driven accelerators for a new frontier
in ultrafast physics
Brendan Dromey
Studying nascent proton driven radiation
chemistry in H2O in real timeSPIE Prague, 2nd April 2019
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Acknowledgments
• Mark Coughlan • Balder Villa-Gomez• Mark Yeung• Hannah Donnelly• Nicole Breslin• Christine Arthur• G. Nersisyan
• M. Zepf
• Rong Yang• Martin Speicher• Jorg Schreiber
SPIE Prague, 2nd April 2019
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Overview
•Ultrafast sources of laser driven radiation
•Optical streaking technique
•Pulsed radiolysis in SiO2: The role of dimensionality
•Pulsed radiolysis in H2O: Solvated electron dynamics on ultrafast timescales
SPIE Prague, 2nd April 2019
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Laser driven ion accelerators – a novel source for ultrafast physics
H. Schwoerer, “Laser-plasma acceleration of quasi-monoenergetic protons from microstructuredtargets”, Nature, 439, 445-448, 2006
Traget Normal Sheath Acceleration, TNSA
PIC simulation: Broadband energy spectrum
1
10-2
10-4
10Energy (MeV)
Sharp high energy cut off
By slowing and stopping lower energy components of the ion energy spectrum the ultrafast pulse duration can be recovered to
permit ultrafast pulsed radiolysis
Velocity dispersion
E
Time (ps)
1 ps
Phase space rotation
~ 100 ps
Critically, ultrafast pulse duration is
preserved in narrow energy bandwidths of
the TNSA spectrum
SPIE Prague, 2nd April 2019
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Transparent Dielectrics (or aqueous solutions)
Standard pump probe approach…….
SPIE Prague, 2nd April 2019
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Observing ultrafast proton interactions in a single shot
Schematic(not to scale)
Probe ion induced a) opacity (free electrons in conduction)b) Photabsoption bandsc) Polaristation effects
SPIE Prague, 2nd April 2019
………400 fs to 1.4 ns
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………Ultrafast optical streaking for proton matter interactions
Sample can be Trasparent Dielectric
H2O
Excitation/ionisation to allow free-free absorption of probe photons
Chirped pulse optical streakingExample of normalised transient
opacity data (SiO2)
Dromey et al. “Picosecond metrology of laser-driven proton bursts”, Nat. Comms, 7, 10642 (2016)
Target:H2O, biological samples
Collimating slit
Chirped probe
Ion
pu
lse
SPIE Prague, 2nd April 2019
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0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 100 200
Time from To (ps)
De
pth
into
a-S
iO2
(mm
)
Raw
0.3
0.4
0.5
0.6
0.7
0 200
Y
Z
X
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 100 200
9 MeV
8 MeV
7 MeV
10MeV
Time from To (ps)
9 MeV
8 MeV
7 MeV
10MeV
Calculated 1
0.8
Transm
ission
Dromey et al. “Picosecond metrology of laser-driven proton bursts”, Nat. Comms, 2016
Results: Optical streak of opacity in SiO2
TNSA spectrum1
10-2
10-4
10Energy (MeV)
Sharp high energy cut off
SPIE Prague, 2nd April 2019
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Revealing ultrafast dynamics
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 100 200
Time from To (ps)
De
pth
into
a-S
iO2
(mm
)
Raw
0.3
0.4
0.5
0.6
0.7
0 200
Y
Z
X
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 100 200
9 MeV
8 MeV
7 MeV
10MeV
Time from To (ps)
9 MeV
8 MeV
7 MeV
10MeV
Calculated 1
0.8
Transm
ission
Dromey et al. “Picosecond metrology of laser-driven proton bursts”, Nat. Comms, 7, 10642 (2016)
Experimental Data Modelling
Reveals ultrafast lifetime of electrons in the conduction band < 0.5 ps
SPIE Prague, 2nd April 2019
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1020 cm-3
Transition from free electron gas to electron hole plasma
Exciton (correlated electron hole pair)
formation provides a rapid decay channel
electron is no longer ‘free’
Slow decay
Rapid decay
D. Grojo “Time-Evolution of Carriers after MultiphotonIonization of Bulk Dielectrics” ” IThI3, 2009 OSA/CLEO/IQEC 2009
>1020 cm-3
100 ps
Audebert et al., Space-Time Observation of an Electron Gas in SiO2, PRL 73, 1990 (1994)
“Two speed decay”
(i)
(ii)(iii)
(ii)
(iii)
EElectronHole
Proton
Exciton
Time (fs)
N(e
)
(i)
t ~ 150 fs
Temporal response of SiO2 to ionisation – Exciton formation
SPIE Prague, 2nd April 2019
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Y (
m
)
1
0
X (m)
0
0
1
1
Z (m)
Direction ofpropagation
Y (
m
)
1
00 Z (m)
1
Nanoscale tracks of ion damage from a combination of TRIM calculations (trajectories) and FLUKA simulations (track size) for protons in SiO2
Results suggests near solid density ionisation along each track >1021 cm-3
Electron – Hole plasma conditions not suitable for exciton formation
Why are we seeing an ultrafast response in experiments?
Flux: 50-100 µm-2 – same as the experimental conditions
Nanostructured dose distribution of protons in SiO2
SPIE Prague, 2nd April 2019
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Y (
m
)1
0
X (m)
0
0
1
1
Z (m)
Direction ofpropagation
Y (
m)
1
0 10
X (m)
Such evolution would be consistent with predictions from Monte Carlo simulations for electron diffusivity
Osmani et al. e-J. Surf. Sci. Nanotech. Vol. 8 (2010) 278-282
>1022 cm-3~1018 cm-3
This only the instantaneous picture….. Nanometre scale energy density gradients
3-D
2-D transverse cross section
Hypothesis – rapid evolution of localised free density
SPIE Prague, 2nd April 2019
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log
10
(ne )
log
10
(ne )
After approx. 200 fs near uniform conditions with
~1019 cm-3
Diffusivity – 10 -100 cm2/s
log
10
(ne )
How can we study this quantitatively?
Implied rapid evolution of density (simplified)
SPIE Prague, 2nd April 2019
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Tortuous nanostructured matrix of SiO22-4 nm structures
20 - 30 nm voids
2-4 nm particles of SiO2
SiO2 Aerogel – reduced dimensionality
SPIE Prague, 2nd April 2019
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3D Approx. 1D
2.6 gcm-3 .26 gcm-3 0.8 gcm-3
(schematic, for illustrative purposes only)
SiO2 Aerogel – reducing dimensionality
SPIE Prague, 2nd April 2019
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Results: Optical streak of opacity in ~ 0.26 gcm-3 Aerogel
TNSA ion pulse
Yields direct information about the absolute arrival time of various species
Prompt X-rays/Fast electron pulse – gives very accurate to
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
-300 -100 100 300 500 700 900
SPIE Prague, 2nd April 2019
No
rmal
ise
d T
ran
smis
sio
n
Time from To (ps)
-
Time from To (ps)
No
rmal
ise
d T
ran
smis
sio
n0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
50 250 450 650 850 1050
Z @ 550 m
Average ‘Z’
Calculated
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
200 400 600 800 1000 1200
No
rmal
ise
d T
ran
smis
sio
n
3.5 ps FWHM< 0.5 ps decay time constant
Nearly 200 ps decay constant
Clear effect of nanostructure
Direct comparison with solid density SiO2
Streaks on the same timescales
SPIE Prague, 2nd April 2019
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Scaling with average density/dimensionalityN
orm
alis
ed
Sig
nal
SPIE Prague, 2nd April 2019
0
50
100
150
200
250
300
350
400
450
500
0.01 0.1 1 10
(Density)-1.1±0.3
Density (g/cm-3)
Re
cove
ry/D
ecay
Tim
e c
on
stan
t (p
s)
0
0.2
0.4
0.6
0.8
1
1.2
283 383 483 583 683 783
2.66 g/cm3
0
0.2
0.4
0.6
0.8
1
1.2
283 383 483 583 683 783
0.26 g/cm3
2.66 g/cm3
0
0.2
0.4
0.6
0.8
1
1.2
283 383 483 583 683 783
0.26 g/cm3 0.09 g/cm3
2.66 g/cm3
0
0.2
0.4
0.6
0.8
1
1.2
283 383 483 583 683 783
0.26 g/cm3 0.09 g/cm3
0.04 g/cm3
2.66 g/cm3
Time from peak ion induced opacityo (ps)
0 100 200 300 400 500
1/e recovery constant
Full transmission
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• Possible to directly measure proton damage in materials (here transparent dielectrics) on ultrafast timescales
• In bulk SiO2 this allows direct measurement of the proton pulse duration.
• Nonlinear variation in recovery times for changing the dimensionality of the interaction for nanostructured SiO2
• Clear conclusion: Reduced dimensionality inhibits the exciton pathway
• Next step: Absolutely verify scaling with average density/dimensionality and underlying physics
Summary SiO2
SPIE Prague, 2nd April 2019
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Addressing the rising incidence of cancer
ULTIMATE GOAL - Improve long term prospects for young patients by reducing damage near the tumor site
Increasing cancer rates, in particular amongst young people (33% since 1993)
http://www.cancerresearchuk.org/
1) Dose escalation and/or
2) Highly targeted dose for radiosensitive treatment sites
Ions -Characteristic
Bragg peak
Dose vs Depth curves
Electrons
X-rays
Protons
Rivista trimestrale dell’Istituto Nazionale di Fisica Nuclearehttp://www.roma1.infn.it/rog/astone/didattica/asimmetrie6.pdf
This is driving major facility development and proliferation
https://www.klinikum.uni-heidelberg.de/
SPIE Prague, 2nd April 2019
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Ultrafast ion interactions in H2O – nascent chemistry
This timeframe has been inaccessible to experimental observation to date
seeds
This prevents the benchmarking of ab initio, or “bottom up”, numerical models
Baldacchino, G., ”Pulse radiolysis in water with heavy-ion beams. A short review” Radiat. Phys. Chem. 77, 1218– 1223 (2008)
This in turn prevents unlocking the predictive power of these models
e-aq is a powerful reducing agent for the cytotoxic HO·
SPIE Prague, 2nd April 2019
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Solvated Electron
SPIE Prague, 2nd April 2019
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Studying the solvation process using ions
SPIE Prague, 2nd April 2019
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Observing ultrafast proton interactions in a single shot
Schematic(not to scale)
Probe ion induced a) opacity (free electrons in conduction)b) Photabsoption bandsc) Polaristation effects
SPIE Prague, 2nd April 2019
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Full modelling of interaction – Geant 4
d2(T)dt2
d(T)dt
SPIE Prague, 2nd April 2019
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Experimental results optical streak of solvated electron dynamics
0
1
2
3
4
5
-500 -300 -100 100 300 500 700 900 1100 1300 1500
ProtonsFast electrons and prompt X-raysD
ep
th (
mm
)
Time from T0=0 (ps)
No
rmalise
d Tran
smissio
n (T)
0
1
SPIE Prague, 2nd April 2019
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Experimental results optical streak of solvated electron dynamics
0
1
2
3
4
5
-500 -300 -100 100 300 500 700 900 1100 1300 1500
ProtonsOnset Fast electrons and prompt X-rays
De
pth
(m
m)
Time from T0=0 (ps)SPIE Prague, 2nd April 2019
d(T)dt
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Mismatch between experiment and theory
Time from T0=0 (ps)
d2(T)dt2
0
1
2
3
4
5
200 300 400 500 600
De
pth
(m
m)
d(T)dt
0
1
2
3
4
5
70 170 270 370 470
Leading edge of opacity
SPIE Prague, 2nd April 2019
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Proton induced dynamics in water – nanocavitation?
Molecular dynamics (MD) simulations indicate a marked difference in H2O response for increasing linear energy transfer (LET)
Simulation input by P. deVera and F. Currell, Univ. of Manchester
SPIE Prague, 2nd April 2019
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Ultrafast implications for nascent water chemistry?
This timeframe has been inaccessible to experimental observation to date
seeds
e-aq is a powerful reducing agent for the cytotoxic HO·
SPIE Prague, 2nd April 2019