Relativistically oscillating plasma surfaces : High harmonic generation and ultrafast plasma...

Relativistically oscillating plasma surfaces : High harmonic generation and ultrafast plasma

dynamics

Brendan Dromey

ICUIL 26 Sept – 1 Oct Watkins Glen NYBrendan Dromey [email protected]

Acknowledgements

Brendan Dromey [email protected]

Experiments: PIC-Simulations:• R. Hörlein• Y. Nomura• D. Kiefer• P. Heissler• G. D. Tsakiris

• S. Rykovanov

Max Planck Institute for Quantum Optics

IESL, FORTH, Heraklion Crete:

• P. Tzallas• D. Charalambidis

Queens University Belfast:

• M. Yeung• D. Adams • M. Geissler• M. Zepf

ICUIL 26 Sept – 1 Oct Watkins Glen NY

LANL, Trident

• D. Jung• B. M. Hegelich

STFC Central Laser Facility

• P. Foster• C. Hooker• D. Neely • P. Norreys

Outline

• Low and high contrast interactions

• High order harmonic generation (HOHG) from solids

• keV harmonic generation

• Role of surface roughness – ultrafast laser driven plasma dynamics

• Divergence of HOHG

• Novel results for HOHG transmitted through thin foils scaling in the relativistic limit

[email protected] 26 Sept – 1 Oct Watkins Glen NYBrendan Dromey

Contrast in a laser system


Slide courtesy of R. Marjoribanks


Contrast improvement in a laser system


AR coated

Contrast increased by ~102 per plasma mirror used

1014 to 1015 Wcm-2

Plasma mirror


Petawatt class interactions


Andor CCD detector

Target – CH (5-10 nm rms)

Double plasma mirrorIncident laser pulse: f3 cone

Vulcan Petawatt at RAL: ~600J in 500fs ~ 1053nm

1200 lines per mm flatfield grating

Gold collection mirror


Low Vs high contrast


Spectrum with plasma mirror – High harmonic generation, scaling in the relativistic limit

B. Dromey et. al., Nature Physics, 2, 456 (2006)

Spectrum with no plasma mirror

7mm

17nm ~2nm


Relativistically oscillating plasmas


• The target surface is highly ionised by the leading edge of the pulse – becomes rapidly over dense (reflecting to incident radiation)

• The collective electron motion created by the incident electromagnetic wave can be considered as an oscillating mirror

Incident pulse

Reflected pulse

Oscillating critical density surface

Illustration from George TsakirisNew Journal Physics 8, 19, 2006


Einstein's Relativistic Doppler effect - 42

Oscillatory extension to Relativistic Doppler effect

γs

t´

vs

c

t´

cvs

Universal spectrum381 nIn

Extended Roll-over

nmax 81/2 3

T. Baeva, S. Gordienko, A. Pukhov, Phys. Rev. E, 74, 046404 (2006)

Relativistic Spiking

Brendan Dromey [email protected] 26 Sept – 1 Oct Watkins Glen NY

= n-2.66

Important properties of ROM


•Phase locked to driving laser – no phase matching required

•Both odd and even orders generated

•Generation process saturates in the relativistic limit

•High conversion efficiency – scaling as n-2.66, where n is harmonic order

•Harmonic width greater than separation for keV energies

•Rapid scaling to high orders with driving laser intensity

•Filter to obtain train of attosecond pulses

•No chirp


Coherent wake emission


Plexiglass Target (Density ~1.3 g/cm^3):Glass Target (Density ~2.6 g/cm^3):

1113 121417 1516 1113 121415


Brunel electrons

Relativistic plasma harmonics – salient results


~p

26 24 22 20 18 16 14 Harmonic order (n)

ROM

Individual pulse duration: 900 400 as

Attosecond Phase LockingDiffraction limited performance

From ‘Y. Nomura et al, Nature Physics, 5, 124 - 128 (2009)

From ‘B. Dromey et al, Nature Physics, 5, 146 - 152 (2009)

Exceptional coherence properties of the driving laser transferred to the XUV


Petawatt class interactions


Image plate detector

Target – CH (5-10 nm rms)

Double plasma mirrorIncident laser pulse: f3 cone

Vulcan Petawatt at RAL: ~600J in 500fs ~ 1053nm

Mica crystal,

Von Hamos geometry


ROM harmonics – Petawatt class


keV ROM harmonics and the efficiency roll-over

B. Dromey et al., Phys. Rev. Lett. 99, 085001 (2007)

10

1

10-1

10-2

Inte

nsity

/arb

. uni

tsN

orm

alis

ed a

t 120

0th o

rder

Harmonic order, n1500 3000

a) (1.5±.3)1020Wcm-2

b) (2.5±.5)1020Wcm-2

Photon Energy, keV

2000 2500

1770 2360 2950 3530

p=2.8

p=2.4

Prel=2.55 (+0.25, -0.15)

namax> 2600

nbmax>3000

Intensity dependent rollover

Focused Int

Prel

n-p


How can we see keV harmonics?


DfSurface roughness - Fourier analysis

Angstrom wavelength lengths beamed from nm roughness targets?


Motion under the influence of normally incident, linearly polarized EM wave, bound to an immobile ion background via charge separation fields

4 cycles FWHM Gaussian pulse, ao= 10 , ne = 400nc

Density gradient from 1-D

PIC, same parameters

Electron capacitor model


Complete discussion given in: Rykovanov et al arXiv:0908.3134v2 [physics.plasm-ph]


http://arxiv.org/abs/0908.3134v2


L =800nm, 4 cycle pulse, h = 40nmm, a0 =5 (corresponds to > 1019Wcm-2)

Snap shots from Simulation – over a single cycle in the rise of the pulse

Ultrafast plasma dynamics: 2-D PIC simulations

Complete discussion given in: Rykovanov et al arXiv:0908.3134v2 [physics.plasm-ph]

h


http://arxiv.org/abs/0908.3134v2


23242526 22 21 20 19 18 17 16 15 14

GratingAu Mirror

Detector

HOHG Source

Astra laser at RAL: 10Hz ~1.5J in 40fs ~ 800nm

Astra at RAL: 10Hz ~1.5J in 40fs ~ 800nm

Off-axis emission CWE only

On-axis emission - CWE and RomO- axis emission - Rom only


Insensitivity to surface roughness


From ‘B. Dromey et al, NATURE Physics, 5, 146 - 152 (2009)

22 20 18 16Harmonic Order

37 35 33 31 29 27 25 23

Coun

ts (

104 )

2

1

0.5

1.5

Harmonic Order

x

y rms <1nm

rms ~18nm

38

Spectra same to within 1 standard deviation for factor of >10 increase in roughness


Divergence of HOHG


Harmonic Spectra: total power emitted

10

1

10-1

10-2

Inte

nsity

/arb

. Uni

ts N

orm

alis

ed a

t 120

0th o

rder

Harmonic order, n1500 3000

a) (1.5±.3)1020Wcm-2

b) (2.5±.5)1020Wcm-2

Photon Energy, keV

2000 2500

1770 2360 2950 3530

Prel=2.55 (+0.25, -0.15)


Harmonic divergence


Flat surface

Harmonics emitted with intrinsic divergence

If all orders diffraction limited - expect a much flatter spectrum

θ

L

θL/n

Diffraction limited peformance would suggest harmonic~Laser/n harmonic~10-4 rad for keV harmonics.


Uniform harmonic divergence


Curved surface

Harmonics emitted with divergence given by the curved surface

D

-All orders identical divergence-Beam still focusable to diffraction limitfor spherically bent surface.


Divergence measurements


Grating

Detector

Source

On axis

Grating

Detector

Source

On axis

-1nm

1nma) <1nm rms i) Orders 17-39

Spectrometer configuration Recorded spectra

Angle (mrad)

39th (~20.5nm )

20th (~40nm)

19mrad 1/e2

a) b)

-60 -40 -20 0 20 40 60

0.1

0.3

0.5

0.7

1.1

20

10

30

40

Angl

e

(mra

d)

Wavelength (nm)

CWEordersROM

orders

Inte

nsity

, arb

. uni

ts

Diffraction limited divergence

20 25 30 35 40 45 50

B. Dromey et al, Nature Physics, 5, 146 - 152 (2009)


ROM in transmission:

H. George, et al., NJP, 9, 113028 (2009)

Experimental results: K. Krushelnick, et al., PRL, 100, 125005, (2008).

ROM harmonics in transmission


targetincident

beam

MCP-detector

collectionmirror

grating

entranceslit


Shortpulse-Beam: 500fs, 125J, 250 TW (1054nm)

Trident laser - Los Alamos national labs




23rd

33rd

Detector position 1Detector position 2

17nm

Al L-edge

61st

53rd

43rd

26nm 45nm


Raw data from CCD



Harmonic orders 24 - 60

Har

mon

ic in

tens

ity n

orm

alis

ed t

o th

e 33

rd h

arm

onic

125 and 200nm Diamond like carbon

Recall from the theory of relativistic

spikes efficiency scaling is expected

as

n-2.66

ROM harmonics the full picture


B. Dromey et. al., Nature Physics, 2, 456 (2006)

Harmonic orders 24 - 60

Ha

rmo

nic

inte

nsi

ty n

orm

alis

ed

to

th

e

33rd

ha

rmo

nic

Ha

rmo

nic

inte

nsi

ty n

orm

alis

ed

to

th

e

23

8rd h

arm

on

ic

Ultrathin thin foil at solid density

ROM harmonics for radial density profiling


Red triangles on Figure

For more detail:

Rainer HoerleinThursday 11:00am

Experimental geometry

200nm

80nm

Summary


•Very high harmonics possible from the relativistic plasma medium

•Diffraction limited performance and attosecond phase locking

•Ultrafast laser driven plasma dynamics – allows beamed keV radiation

•Target denting – possible to shape targets to control divergence

•Transmitted HOHG – novel ROM source

•Use as an ultrafast broadband density diagnostic



Ultrafast broadband density diagnostic

Single foil 125nm,Slow drop in signal to higher orders (~relativistic limit scaling)

With Secondary foil (80nm)Plasma Absorption, up to plasma frequency

With secondary foil (200nm)Strong Carbon absorption

28th

23rd

45nm 30 nm

O2 17.1nm line in second order


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