"Fotonica degli alti campi per la generazione di radiazione X ad impulsi ultracorti" I ntense L aser...

"Fotonica degli alti campi per la generazione di radiazione X ad

impulsi ultracorti"

IIntense ntense LLaser aser IIrradiation rradiation LLab.ab.

Leonida A. Gizzi

CONSIGLIO NAZIONALE DELLE RICERCHEIstituto per i Processi Chimico-Fisici, Pisa, Italy

CONSIGLIO NAZIONALE DELLE RICERCHEIstituto per i Processi Chimico-Fisici

Leonida A. GIZZI, U. Tor Vergata, 13 febbraio 2006.

People• Antonio GIULIETTI (CNR)*• Danilo GIULIETTI (Univ. Pisa)*• Leonida A. GIZZI (CNR)*• Paolo TOMASSINI (CNR)*

• Marco GALIMBERTI (CNR)*

• Luca LABATE (CNR)*

• Petra KOESTER (CNR & Univ. of Pisa)

• Tadzio LEVATO (CNR & Univ. of Pisa)

• Andrea GAMUCCI (CNR & Univ. of

Pisa)

• Walter BALDESCHI (CNR)

• Antonella ROSSI (CNR)

* Also associated with INFN, the Nat. Institute of Nuclear Physics

http://ilil.ipcf.cnr.it

Area della ricerca CNR, Pisa

The ILIL GROUPThe ILIL GROUP

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.



Outline

1. X-RAYS FROM LASER-PLASMAS: Studies on X-ray Emission Dynamics

2. APPLICATIONS OF LP X-RAY SOURCES: Monochromatic µ-Imaging for Differential Absorption

3. R&D ON ULTRAFAST, LASER-DRIVEN X-RAY SOURCES: Preliminary results and future experiments



Basic hydrodynamics of laser-solid Basic hydrodynamics of laser-solid interactionsinteractions

X-ray emission from laser-solid interactions occurs in a narrow layer at the critical density

X-ray emission from laser-plasmas: recent results …

Atomic--physics issues can be investigated via X-ray emission using this interaction scheme



Transient ionization in laser-Transient ionization in laser-plasmas plasmas

Ionization from a charge state Z to a charge state Z+1

10 -12

10 -11

10 -10

10 -9

10 -8

0 200 400 600 800 1000

Be-like to Li like AlLi-like to He like Al

He-like to H like Al

Electron Temperature (eV)

ne=1.0×10 21 cm-3

Calculations show that relaxation time from He-like to H-like Al is comparable to the rise-time of nanosecond pulses


€

NZ : population of charge state Z

€

ScZ and SR

Z : collisional and photo - ionisation rate from charge state Z

€

α3bZ +1 and α RR

Z +1 : three - body and rad. rec. rate from charge state Z +1



Detailed descriptionDetailed descriptionFull description of transient ionisation in plasmas Full description of transient ionisation in plasmas requires that both atomic physics and hydrodynamics requires that both atomic physics and hydrodynamics

are taken into account.are taken into account.


[1] Christiansen et al., Comput.Phys.Commun. 7, 271 (1974)[2] Pert G.J., J. Comput. Phys. 43, 111 (1981)

Examples of Hydrodynamic codesMedusa[1] 1-DPollux[2] 2-D

Hydrodynamic properties of plasmas (electron Hydrodynamic properties of plasmas (electron density and temperature, expansion velocity density and temperature, expansion velocity etc.) can be modelled using Lagrangian or etc.) can be modelled using Lagrangian or

Eulerian numerical codesEulerian numerical codes

Examples of Atomic Physics codesRATION/FLY[3]

Similarly, a description of atomic physics and X-ray emission properties of laser-plasmas can be obtained from numerical codes that account

for a collisional-radiative equilibrium

[3] Lee et al.., J. Quant. Spectrosc. Radiat. Transfer 32, 91 (1984)



2D Map of X-ray emission2D Map of X-ray emissionMap of the electron temperature of the plasma produced by laser Map of the electron temperature of the plasma produced by laser

irradiation of a solid Al target at the peak of a 3ns gaussian laser irradiation of a solid Al target at the peak of a 3ns gaussian laser pulse as predicted by POLLUXpulse as predicted by POLLUX

X-ray emissivity is calculated from electron density and temperature maps given by POLLUX using the code RATION/FLY


Laser

Al He-α

Intensity on Intensity on targettarget::1E14 W/cm1E14 W/cm22

Pulse durationPulse duration::3 ns gaussian3 ns gaussianLaser focal Laser focal spot:spot:8µm8µmTarget:Target:50 µm thick Al50 µm thick Al

Laser



Total simulation time: 2 nsFrame every 200 ps

Target surfaceTarget surface10µm

Hydrodynamics and X-ray emissionHydrodynamics and X-ray emission

X-ray emission at 1.6 keV (He-like Al 1s2-1s2p) from a plasma produced by laser

irradiation of an Al target

Electron density and temperature maps obtained from hydrocode (POLLUX) are post-processed using time-dependent X-ray emission code (FLY)

Laser pulse, 3ns FWHM


QuickTime™ and aVideo decompressor




Thin emission layer assumptionThin emission layer assumption

Most of X-ray emission is found to Most of X-ray emission is found to originate from a thin layer of plasmaoriginate from a thin layer of plasma

10

100

1000

1020

1021

1022

2 3 4 5 6 7 8

Electron Temperature (eV) Electron density (cm

-3)

Time (ns)

Te

Ne

with well-defined density and temperature conditions.

Thin X-ray emitting region


0

0.2

0.4

0.6

0.8

1

40 60 80 100 120 140

-1.5-1.0

-0.5Peak of Pulse+0.5+1.0+1.5

Distance (µm)



Transient ionisation in Transient ionisation in laser-plasmaslaser-plasmas

3ns FWHM pulse is peaked at 4.5 ns

Early during Early during the emission, the emission, time dependent time dependent and steady-and steady-state model state model show different show different results. Later results. Later on, both on, both models give an models give an identical identical ratio. ratio.

Observable:temporal evolution of LyObservable:temporal evolution of Lyαα to He to He intensity ratio:intensity ratio:

Steady-State Steady-State versusversus Time-dependent modelling Time-dependent modelling

0.01

0.1

1

3.5 4 4.5 5 5.5

Steady-StateTime-Dependent

Time (ns)

Lyα

/He

intensity ratio

TD

SS




The experimental The experimental techniquetechnique

Tight-focus irradiation of solid target using Tight-focus irradiation of solid target using cleanclean (temporally (temporally and spatially) and spatially) laser pulselaser pulse


100.0 mm

100.7 mm

101.4 mm

102.1 mm

103.4 mm

f =10 cm10 µm

High quality, near diffraction limited focal spot

•YLF oscillator, 1053 nm•Phosphate amplifiers•3, 7, 20 ns, 2 beams•Single longitudinal mode•Intensity on target•up to: 5 1015 Wcm-2



The X-ray spectraThe X-ray spectraX-ray spectroscopy of K-shell emission from H-like X-ray spectroscopy of K-shell emission from H-like

and He-like Al ionsand He-like Al ions

TargetLens

Crystal

Filter

CCD

Shield0.7 mm Pb

Laser

λ

x

He-α-Ly α-He -He γ-Ly

.

1

2

3

4

5

X-ray spectra must be resolved in time X-ray spectra must be resolved in time to obtain the temporal evolution of to obtain the temporal evolution of H/He line ratios early during H/He line ratios early during irradiation. An X-ray streak-camera is irradiation. An X-ray streak-camera is used.used.


1 ns

λ

Raw data at low sweep speed

QuickTime™ and aPhoto - JPEG decompressor



Leonida A. GIZZI, U. Tor Vergata, 13 febbraio 2006.Cross-calibration of Cross-calibration of spectraspectra

Corrected and calibrated spectrum of early-stage X-ray emission at higher temporal resolution

Cross-calibration

Simultaneous time integrated spectrum is taken along an equivalent line of sight

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.




EXPERIMENTAL RATIO vs TIMEEXPERIMENTAL RATIO vs TIME

LyLyαα to He to He intensity ratio from time- intensity ratio from time-resolved X-ray spectraresolved X-ray spectra

0

0.2

0.4

0.6

0.8

1

1.2

1.4

3.5 4 4.5 5 5.5Time (ns)



Leonida A. GIZZI, U. Tor Vergata, 13 febbraio 2006.Evidence of transient Evidence of transient ionisationionisation


Early during Early during the emission, the emission, time dependent time dependent and steady-and steady-state model state model show different show different results. Later results. Later on, both on, both models give models give identical identical ratio. ratio.

Temporal evolution of LyTemporal evolution of Lyαα to He to He intensity intensity ratio:ratio:

Steady-State Steady-State versusversus Time-dependent modelling Time-dependent modelling

0.01

0.1

1

3.5 4 4.5 5 5.5

Steady-StateTime-Dependent

Time (ns)

Lyα

/He

intensity ratio

TD

SS



Leonida A. GIZZI, U. Tor Vergata, 13 febbraio 2006.Evidence of transient Evidence of transient ionisationionisation

Temporal evolution of LyTemporal evolution of Lyαα to He to He intensity intensity ratio:ratio:

Experiment versus Experiment versus SS/TDSS/TD modelling modelling

L.A.Gizzi et al., Letter on Phys. Plasmas, (2003); L.Labate et al; Phys. Plasmas (2005).

Early during Early during the emission, the emission, time dependent time dependent and steady-and steady-state model state model show different show different results. Later results. Later on, both on, both models give models give identical identical ratio. ratio. Early Early stage stage experimental experimental ratio agrees ratio agrees well with well with tdtd calculations.calculations.


0.01

0.1

1

3.5 4 4.5 5 5.5

ExperimentalSteady-StateTime-Dependent

Time (ns)

Lyα

/He

intensity ratio

TD

SS

Experiment




Monochromatic µ-imaging with curved crystals

Applications of LP X-ray sources:monochromatic µ-imaging …



*)Pikuz et al., Laser and Particle Beams,19:285, 2001 Sanchez del Rio et al., Review of Scientific Instr., 72:3291, 2001

OC =R

OS=a

OI1 =p

OI2 =q

X-ray Crystal Imaging Microscope X-ray Crystal Imaging Microscope *)*)

Source on Rowland circle:

q=R

sinϑo

M =cot2 ϑo1

1−p/ a

“Image plane” at a distance q from the crystal given by the condition of equal vertican and horizontal magnification :Ωh

r(q−bh)Ωh

i (a−p)=Mh =Mv =

Ωvr (bv −q)

Ωvi (a−p)

Focusing condition: Ωhr bh =Ωh

i a

Ωvr bv =Ωv

i a



x/mm

Source on Rowland Circle: a = a(R)

a<a(R)

a<a(R)

a>a(R)

a>a(R)

y/mm

Horizontal plane

When the source is on the Rowland Circle,When the source is on the Rowland Circle,the reflected spectral range is minimum: the reflected spectral range is minimum: the crystal behaves as a monochromatorthe crystal behaves as a monochromator..

0= 0.894 rad2d = 19.9Å

R = 150 mm

Vertical plane

Reflected WavelengthsReflected Wavelengths



XCIM (X-ray Crystal Imaging Microscope*) scheme allows monochromatic radiography of thin objects with µm resolution to be obtained

*) T.A. Pikuz et al., Laser Part. Beams 19,285 (2001); M. Sanchez del Rio et al., Rev. Sci. Instrum. 72, 3291 (2001)

XCIM scheme is based upon the use of a spherically bent crystal

C++, fully object-oriented code

X-ray Crystal Imaging Microscopy scheme

arbitrary shapes and sizes of the source can be considered

different forms of the crystal rocking curves can be taken into accounttypical running times: 5min for 5x106 sampled rays (Linux based P4)

Ray-tracing Ray-tracing simulationssimulations of X-ray µ- of X-ray µ-radiographyradiography#)#)

#)#) L.Labate et al., Ray-tracing simulation of an X-ray optics based upon a bent crystal for differential absorption applications, LPB, 2004.

Ray-tracing simulations of the system with the ORTO ray-tracing code**):





X-ray intensity distribution at the image point using an Al plasma source and the crystal set to focus near the Heα line(no objects)

Al Heα lineAl IC line

Ray-tracing simulations: horizontal Ray-tracing simulations: horizontal focusfocus

Spherical aberration and astigmatism: intensity

distribution around the horizontal focus (without

objects)





Ray-tracing of the XCIM scheme with Fresnel zone plate as a test object

X-ray pattern at different crystal-detector distances

Ray-tracing simulations: imaging a Ray-tracing simulations: imaging a test objecttest object



The X-ray sourceThe X-ray source

THE DRIVING LASER THE DRIVING LASER

•Nd:YAG oscillatorNd:YAG oscillator

• 6 ns pulse duration6 ns pulse duration

•10 Hz rep rate10 Hz rep rate

•1064, 532 nm1064, 532 nm

• up to 500 mJ/pulseup to 500 mJ/pulse

• up to 5 10up to 5 101313 W/cm W/cm22 on target on target

• PC contr. Sync with targetPC contr. Sync with target

15 µm laser spot on Cu target at 6E12 W/cm15 µm laser spot on Cu target at 6E12 W/cm22

≈≈25 µm FWHM source size25 µm FWHM source size

View: 45° from laser axis



λ0 Åb)

λ00 Åc)

Lithium-likeLithium-like

Monochromatic X-ray Beam from LP X-Monochromatic X-ray Beam from LP X-raysrays

λ02 Å

0

Central wavelength on crystal:

a)

He αIC

Target: Al, Intensity on target: 2E13W/cm2

1

0.5

L.A.Gizzi et al.., Towards differential micro-imaging using a laser-plasma soft X-ray source, LPB (2004); S.Laville et al., NIM A (2005)



Image resolution:

€

Δxh =16.8 ± 2.3μm; Δxv = 52.3± 9.1μm

Test image with XCIM Test image with XCIM configurationconfiguration

Image of a Frenel Zone plate with a monochromatic beam at 1.6 keV (Al He-α line)

100 µm

FH

FV

S

O

Object « imaging » plane

Rowland circle

HiΩ

ViΩ

VrΩ

HrΩ

I2

θθ

I1

100 µm

Contact image on X-ray film

CCD Image



Source characterisation using a Source characterisation using a zone-platezone-plate

A Fresnel zone-plate with known geometrical properties is used as a sample to determine magnification and resolution

properties of the imaging system

0

1

0

500

1000

1500

2000

2500

0 500 1000 1500 2000 2500distanza ( m)

Source Profile:

€

f (x) = Ae− ( x−xo )2

2σ 2

Sample Profile:

g(x) =ϑ (x−sO )

I(x) =aerfx − ′ x o

2 M −1( )σ

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ +d

Space resolution condition: Δx = 2

Image profile:

A 26 µm (FWHM) source size (PLX@ILIL) yelds a resolution of approx. 20µm at the object plane

X-ray image of a zone-plate: M=4.7

Radial line-out of image

Resolution definitions using a step-function



Δt(x,y) =lnI1(x,y)I01(x,y)

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ −ln

I2(x,y)I02(x,y)

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ = Δμi ρi x,y,z( ) dz

campione∫

i∑

Difference in optical depth:

Detection Limit: Δ=1.310-7g/cm2

Δσ =Δ(Δμ)Δμ2 ln I

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2

+ΔI

I Δμ

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2

Δ = (1506 10)cm2/gΔI/I = 10-4

DIFFERENTIAL ABSORPTIONDIFFERENTIAL ABSORPTION

λ1

λ2

Br C

An example: bromine and carbon



0.2 l of a 0.265 g/ml solution of LiBr

washer

substrate

Δ=1210.5 cm2/g

Δt = -0.9±0.1EXPECTED OPTICAL DEPTH

DIFFERENCE

lnmI1

mI01

mI02

mI2

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ =−1.1±0.8

MEASURED OPTICAL DEPTH

DIFFERENCE

1λ1 = 7.75 Å

1

0

Incident beam

Transmitted beam I1

0λ1

λ

1

0

1

0

Incident beam

Transmitted beam

λ2 = 7.78 Å

λ2

λ

DIFFERENTIAL ABSORPTION OF A TEST SAMPLE



ELEMENTAL 2D MAPPING ELEMENTAL 2D MAPPING Measurements on test-samples obtained from LiBr Measurements on test-samples obtained from LiBr

solutions with two different average solutions with two different average concentrationsconcentrations

P. Koester et al.., Quantitative analysis … submitted to Appl. Phys. B (2005).



ACCESSIBLE PHOTON ENERGIES ACCESSIBLE PHOTON ENERGIES

Up to Z=22-23, He-α K-shell emission lines can be obtained using small

10 Hz Nd lasers.

At higher Z, emission originate from L and M

shells

Hydrogen-like Helium-likeElement 2p1/2 2p3/2 2p 3P1 2p 1P1 (eV)13 Al 1727.7 1729.0 1588.3 1598.414 Si 2004.3 2006.1 1853.9 1865.115 P 2301.7 2304.0 2140.3 2152.616 S 2619.7 2622.7 2447.3 2460.817 Cl 2958.5 2962.4 2775.1 2789.818 Ar 3318 3323 3124 314019 K 3699 3705 3493 351120 Ca 4100 4108 3883 390321 Sc 4523 4532 4295 431622 Ti 4966 4977 4727 475023 V 5431 5444 5180 520524 Cr 5917 5932 5655 568225 Mn 6424 6442 6151 618126 Fe 6952 6973 6668 670127 Co 7502 7526 7206 724228 Ni 8073 8102 7766 780629 Cu 8666 8699 8347 839230 Zn 9281 9318 8950 899931 Ga 9917 9960 9575 9628



2 3 4 5 6 7 8 9 10 11 12 13

Wavelength (Å)

0

50

100

150

3.6 3.8 4 4.2 4.4

Date: 14/03/02# shot: 13

Intensity [A.U.]

Wavelength [Å]

Heγ He

1Li s

22 p2

-1 2 3 P s p p

Heα

1Li s

22 p2

-1 2P s p

2 2S

1Li s

22 p2

-1 2P s p

2

ChlorineChlorine

0

20

40

60

80

100

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9

Date: 14/03/02# shot: 20

Intensity [A.U.]

Wavelength [Å]

Cl He

Ca He

α

Cl He

γ Cl He

δ

CalciumCalcium

““Tunability” of the PLX sourceTunability” of the PLX source

104

105

106

107

5 5.5 6 6.5 7[Å]λ

SiliconSilicon

CopperCopper

0

50

100

150

200

2.61 2.62 2.63 2.64 2.65

Date: 06/06/02# shot: 3

1Li s22 p 2 -1 2P s p 2 2P

[ ]Wavelength Å

TitaniumTitanium Alluminium

CopperCopper

Moliben. CopperCopper



R&D on K-apha, laser driven, ultrafast X-ray sources



Studi di fenomeni su scale temporali e spaziali atomiche

• Sorgenti Kα da Plasmi-Laser• Scattering Thomson[1]• X-ray Free Electron Laser[2]• Slicing (SR)

•Cristallografia risolta nel tempo[3]•Studi dinamici di transizioni di fase[4]•Applicazioni bio-mediche[5]•Nanolitografia• …Referenze:[1] P. Tomassini et al. Applied Physics B, 80:419–436, 2005. [2] L. Serafini et al. Nuclear Instruments & Methods A, 528(1-2):586–590, 2004.[3] A. Rousse et al. Reviews of Modern Physics, 73:17–31, 2001.[4] K. Sokolowski-Tinten et al. Nature, 422:287–289, 2003. [5] R. Neutze et al. Nature, 406:752–757, 2000.

Sorgenti X ad impulsi ultracorti



• Dimensione della regione di emissione paragonabile alla dimensione dello spot focale del laser[1].• Durata dell’emissione Kα paragonabile alla durata dell’impulso laser[2,3].• Emissione isotropa. • Efficienza di conversione di energia laser in radiazione Kα fino a 10-4[4].• Frequenza di ripetizione fino ai kHz.• Sistemi compatti (table top)Referenze:[1] Ch. Reich et al. Physical Review E, 68:056408, 2003..[2] J. Limpouch et al. Czechoslovak Journal of Physics, 52:D342–D348, 2002.[3] Ch. Reich et al. Physical Review Letters, 84:4846, 2000. [4] H. S. Park et al. Review of Scientific Instruments, 75(10):4048–4050, 2004.

Sorgenti X da interazione laser-solido



BASIC MECHANISM: INNER SHELL TRANSITIONSBASIC MECHANISM: INNER SHELL TRANSITIONS

The interaction of focused, intense CPA (Chirped Pulse Amplification) laser pulse with a solid target produces “hot” electrons that penetrate in the cold target substrate and generate incoherent X-ray emission (K-shell transitions).

Laser

K-a X-ray emission

Ionised plasma X-ray emission

Laser heated plasma

Fast electron heated solid

Fast electrons



QuickTime™ and aTIFF (LZW) decompressor


- generazione di onde elettrostatiche longitudinali (onde di plasma)

- smorzamento non collisionale delle onde o accelerazione (WF, SMWF, Pond. Acc. …)

- generazione di elettroni ‘veloci’.- ionizzazione della K-shell degli atomi del bersaglio per impatto degli elettroni- transizioni radiative > emissione di righe K

Generazione di radiazione Ka



Polarizzazione della radiazione laser nel piano di incidenza (p) e angolo di incidenza non-zero.

=>Campo elettrico del laser ha una componente lungo il gradiente di

densità del plasma.=>

Generazione di un’onda di plasma in vicinanza della densità critica, dove pe= Laser.



laser

densità critica

Onda di plasma

Assorbimento risonante



•Il regime di interazione di un impulso laser intenso ed ultracorto (decine di fs) è caratterizzato da un plasma denso con gradienti molto ripidi. La generazione di elettroni ‘veloci’ e quindi la produzione di radiazione Kα è particolarmente efficiente per impulsi laser ultracorti [1]. •Efficienza di conversione di energia laser in radiazione Kα e caratteristiche spaziali dell’emissione X sono stati misurati per un ampio range di intensità della radiazione laser (1015 -1019 W/cm2 ) [2,3,4]. •Dimensioni della regione di emissione Kα da poche volte a diverse decine di volte le dimensione dello spot focale del laser sono state misurate [3,5,6].•Misure di correlazione indicano una durata dell’impulso X di alcune centinaia di femtosecondi [7].

Referenze:[1] D. Salzmann et al. Physical Review E, 65:036402, 2002. [2] Ch. Reich et al. Physical Review Letters, 84:4846, 2000. [3] D. C. Eder et al. Applied Physics B, 70:211–217, 2000.

[4] F. Ewald et al. Europhysics Letters, 60(5):710–716, 2002.[5] Ch. Reich et al. Physical Review E, 68:056408, 2003. [6] G. Pretzler et al. Applied Physics Letters, 82(21):3623–3625, 2003. [7] T. Feurer et al. Physical Review E, 65:016412, 2001.

Caratteristiche principali



Experimental technique

10 Hz rep rate fs laser pulse

Optical spectroscopy on reflected and diffused radiation



The femtosecond laser system



Laser pulse width measurements

Time scan

photomultiplier

BBO crystal

Laser

Zero-signal auto-correlator for high dynamic range measurement•Aimed at >106 peak-power to ASE contrast ratio

10-5

10-4

10-3

10-2

10-1

100

101

-800 -600 -400 -200 0 200 400 600 800

Time (fs)

Ti:Sa oscillator pulse

Gaussian fit

M.Galimberti et al., IPCF-Report 2004

The SH autocorrelator



Autocorrelator for ASE characterisation

Time scan

photomultiplier

BBO crystal

Laser

Zero-signal auto-correlator for high dynamic range measurement•Aimed at >106 peak-power to ASE contrast ratio

Amplified Pulse

Gaussian fit

M.Galimberti et al., IPCF-Report 2004



Autocorrelator for ASE characterization(200 ps range)

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

-2 10-10 -1.5 10-10 -1 10-10 -5 10-11 0

Time (fs)

Measurement carried out by Amplitude Tech. using a SEQUOIA autocorrelator



Profilo spaziale dell’impulso laser

0

500

1000

1500

2000

2500

3000

300 320 340 360 380 400Position (µm)

0

200

400

600

800

1000

95 100 105 110 115 120 125 130 135

Half Width (1/e) (µm)FWHM (µm)

Distance from lens (cm)

Piano equivalente con lente con focale di ca. 100 cm

Spot focale di FWHM=15mper la lente di 14cm focale

• 12 mJ• 67 fs• 15 m

Intensità sul bersaglio fino a1017 W/cm2

Beam quality



Raw data from X-ray crystal spectrometer

Crystal tuning spectrum using resonance line emission from He-like Aluminium (He-alpha line@1588 eV) from nanosecond irradiation (reference emission).

Heα

h

Same spectral range, with femtosecond pulse and poor compression (≈10 ps pulse).

HeαKα(1486.70 eV)

h

Single-pixel noise arises from K-alpha photons and/or energetic electrons



Single-Photon X-ray Spectroscopy (SPS)

Spectral analysis of X-rays generated by femtosecond laser-plasma interactions is performed by using a low noise CCD array

to measure the charge produced by each photon

The X-ray flux incident of the CCD array is controlled to ensure that the average number of photons per pixel is much less than one.• The image shows the result obtained with a Peltier cooled, 16 bits ccd array, after exposure to X-rays produced by a single femtosecond laser-target interaction event.



The total crystal to CCD camera distance is about 1m in order to:

get a low photon flux (0.02 photons/pixel)

collect a monochromatic beam onto the CCD sensor (dE/E ~ 5x10-2)

A flat TlAP crystal in a first-order Bragg configuration is used as dispersing element to select a narrow-band beam

The laser plasma source at ILIL (PLX) is used to produce X-rays

Nd:YLF laser

focusing lens

crystalAl filter

Al target

PIN diode(*)

CCD Calibration set-up (<2 keV)



Event identification

Subtraction of local background

Sum of charge over pixels of each event

Histogram of events for each class (one pixel, two pixels etc. …)

Algorithm

L. Labate et al., Nucl. Instr. and Meth. A. 495, 148 (2002)



Calibration histograms

1140 eV

-10

0

10

20

30

40

50

60

70

ADC levels

Counts

20 40 60 80 100 120 140

1320 eV1550 eV

Response of CCD to

monochromatic X-ray

photons at low (<2keV)

photon energy



CCD Calibration curve for SPS

Calibration at higher (>2keV) energy was performed using radioactive sources



Fast electron generation

1

10

100

1000

10000

1000 104 105

Photon energy (eV)

Target: Al (massive)

Al He/K-alpha(1486.70 eV)Lower intensity

1

10

100

1000

10000

1000 104 105


Al He/K-alpha(1486.70 eV)Higher intensity

1

10

100

1000

10000

1000 104 105


Al He/K-alpha(1486.70 eV)High vs. Low Intensity



1

10

100

1000

10000

4000 8000 1.2 104 1.6 104 2 104

X-ray intensity (A.U.)

Photon energy (eV)

Target: Massive Al

High-energy continuum emission

KTe≈1.5keV

KTe≈10keV



K-alpha emission from Si target

4

8

12

16

20

1000 1500 2000 2500 3000Photon energy (eV)

Target: Si plate

Si K-alpha(1739 eV)

Si K-beta(1836 eV)



K-alpha emission from Titanium target

0

100

200

300

400

500

600

700

100 1000 104 105 106

Target: Titanium (solid)

Photon energy (eV)

Ti K-alpha(4510.84 eV)

Escape (4510.84-1739,98 eV=2270,86)





Misure con una CCD in regime a singolo fotone[1]-> risoluzione spettrale-> misura assoluta del flusso di fotoni

-> 107 fotoni/impulso laserReferenze:[1] L. Labate et al. Nuclear Instrument and Method A, 495:148, 2002.

Acquisizione del segnale X ottenuto dall’irraggiamento di un foglio di Ti con un singolo impulso del laser.

Spettro ottenuto dall’analisi di 150 acquisizioni.

La sorgente Kα



Open issues… da affrontare nei prossimi

esperimenti a due fasci



•L’interazione è ricca di fenomeni fisici complessi come la generazione di instabilità [1], la produzione di campi elettrici e magnetici molto intensi [2] ed effetti relativistici [3].•I dati sperimentali non possone essere spiegati tenendo conto soltanto dell’intensità del laser.•La presenza di eventuali preimpulsi e della emissione spontanea amplificata (ASE) può ionizzare il materiale prima dell’arrivo dell’impulso principale anche per laser con un contrasto alto (10-7 - 10-8), per cui l’impulso ai femtosecondi interagisce con un plasma piuttosto che con un solido. Le condizioni di interazione possono cambiare significativamente per profili diversi del preplasma [4].•Le dimensioni della zona di emissione di radiazione dipendono dalle proprietà della popolazione elettronica “veloce” e dall’eventuale presenza di campi magnetici autogenerati

Referenze:[1] William L. Kruer. The physics of laser plasma interactions. The advanced book program. Addison-Wesley publishing company, 1988.

[2] L. A. Gizzi et al. Laser Part. Beams, 13, 1995. [3] Scott C. Wilks and William L. Kruer.IEEE Journal of Quantum Electronics, 33(11):1954–1968, 1997.

[4] S. Bastiani et al. Physical Review E, 56(6):7179–7185, 1997.

Controllo della “sorgente”



HIGH RESOLUTION SPECTRAIdentification …

0

100

200

300

400

500

4000 4400 4800 5200

X-ray intensity (A.U.)

Photon energy (eV)

Target: Titanium (Solid)

K(4.93 keV)

Kα(4.51 keV)

Interplay between plasma emission and K-alpha emission



FORWARD-EMITTED CHARGED PARTICLE DETECTION (preliminary)

Laser

Dose-sensitive radiation detector

(radio-chromic film)

40°

Dose is released along the axis perpendicular to the target.

Laser intensity on target2 x 1017 W/cm2







electrons

Rivelazione degli elettroni con film radiocromici

• emissione in direzione normale alla superficie del bersaglio

• semi-apertura angolare: orizzontale: 20 verticale: 15

Elettroni “veloci”



Simulazione Montecarlo per calcolare la perdita di energia degli elettroni negli strati sensibili dei film radiocromici [1,2].

Gli elettroni emessi dalla superficie posteriore del bersaglio hanno energia tra 40 e 100 keV.

Referenze:[1] GEANT4: LCB Status Report/RD44, CERN/LHCC-98-44 (1998)[2] M. Galimberti et al. Review of Scientific Instruments,

76:053303, 2005.

Elettroni “veloci”



Dipendenza dell’efficienza di conversione di energia laser in radiazione X

dalla polarizzazione della radiazione

laser



Effetti di polarizzazione



Controllo tramite spettroscopia ottica

10

100

1000

10000

100000

0

2000

4000

6000

8000

1 104

400 500 600 700 800

Data from solid target (steel)

Calibration

Intensity (A.U.)

Calibration intensity (A.U.)

Wavelength (nm)

532nm633nm

5 /2

3 /2

2

Spettro della radiazione riflessa dal bersaglio (steel, solid)

La presenza di armoniche intere (2w) o semi-intere (3/2 e 5/2 w) rivelano aspetti sulla

dinamica dell’interazione.



0

0.2

0.4

0.6

0.8

1

500 510 520 530 540 550

Thin foil target:

40 µm polypropylene

Thick target:

solid steel

Intensity (A.U.)

Wavelength (nm)

Comparison between specular second harmonic emission from solid (metal) target and thin foil plastic target. The spectral width (FWHM) in the first case is 7.8 nm, while

in the second case (thin foil) this width is 4.6 nm.

Controllo tramite spettroscopia otticaL’analisi fine degli spettri ottici può

mettere in evidenza fenomeni di propagazione in plasmi preformati.



Upgrade of the fs-system

Doppio fascio: >2TW pump beam e >0.1 Tw probe beamI fasci sono compressi indipendentemente: possibilità di modificare la durata degli impulsi



• Osservata radiazione Kα dall’irragiamento di Al, Si e Ti• La radiazione X emessa è stata risolta spettralmente e il flusso totale di fotoni è stato misurato mediante l’utilizzo di una CCD in regime a singolo fotone.• Caratterizzazione degli elettroni emessi dalla superficie posteriore del bersaglio mediante l’utilizzo di film radiocromici. •Acquisizione di spettri X ad alta risoluzione spettrale con uno spettrometro basato su un cristallo curvo.•Caratterizzazione delle condizioni di interazione (preplasma creato da preimpulsi) attraverso simulazioni idrodinamiche e misure di spettroscopia ottica•Caratterizzazione spaziale della sorgente K α

Conclusioni e prospettive

"Fotonica degli alti campi per la generazione di radiazione X ad impulsi ultracorti" I ntense L aser...

Documents

Transcript of "Fotonica degli alti campi per la generazione di radiazione X ad impulsi ultracorti" I ntense L aser...