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

1. "Fotonica degli alti campi per la generazione di radiazione X ad impulsi ultracorti" Intense Laser Irradiation Lab. Leonida A. Gizzi CONSIGLIO NAZIONALE DELLE RICERCHE Istituto per i Processi Chimico-Fisici, Pisa, Italy

2. The ILIL GROUP • 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

3. Outline • X-RAYS FROM LASER-PLASMAS: Studies on X-ray Emission Dynamics • APPLICATIONS OF LP X-RAY SOURCES: Monochromatic µ-Imaging for Differential Absorption • R&D ON ULTRAFAST, LASER-DRIVEN X-RAY SOURCES: Preliminary results and future experiments

4. Basic hydrodynamics of laser-solid interactions X-ray emission from laser-solid interactions occurs in a narrow layer at the critical density Atomic--physics issues can be investigated via X-ray emission using this interaction scheme X-ray emission from laser-plasmas: recent results …

5. Calculations show that relaxation time from He-like to H-like Al is comparable to the rise-time of nanosecond pulses Transient ionization in laser-plasmas Ionization from a charge state Z to a charge state Z+1 X-ray emission from laser-plasmas: recent results …

6. Detailed description Hydrodynamic properties of plasmas (electron density and temperature, expansion velocity etc.) can be modelled using Lagrangian or Eulerian numerical codes Examples of Hydrodynamic codes Medusa[1] 1-D Pollux[2] 2-D Examples of Atomic Physics codes RATION/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 [1] Christiansen et al., Comput.Phys.Commun.7, 271 (1974) [2] Pert G.J., J. Comput. Phys.43, 111 (1981) [3] Lee et al.., J. Quant. Spectrosc. Radiat. Transfer32, 91 (1984) Full description of transient ionisation in plasmas requires that both atomic physics and hydrodynamics are taken into account. X-ray emission from laser-plasmas: recent results …

7. Intensity on target: 1E14 W/cm2 Pulse duration: 3 ns gaussian Laser focal spot: 8µm Target: 50 µm thick Al Laser Laser X-ray emissivity is calculated from electron density and temperature maps given by POLLUX using the code RATION/FLY Al He-a 2D Map of X-ray emission 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 pulse as predicted by POLLUX X-ray emission from laser-plasmas: recent results …

8. Hydrodynamics and X-ray emission 10µm X-ray emission at 1.6 keV (He-like Al 1s2-1s2p) from a plasma produced by laser irradiation of an Al target Total simulation time: 2 ns Frame every 200 ps Laser pulse, 3ns FWHM Electron density and temperature maps obtained from hydrocode (POLLUX) are post-processed using time-dependent X-ray emission code (FLY) Target surface X-ray emission from laser-plasmas: recent results …

9. Thin X-ray emitting region with well-defined density and temperature conditions. Thin emission layer assumption Most of X-ray emission is found to originate from a thin layer of plasma X-ray emission from laser-plasmas: recent results …

10. Transient ionisation in laser-plasmas Observable:temporal evolution of Lya to Heb intensity ratio: Steady-State versus Time-dependent modelling Early during the emission, time dependent and steady-state model show different results. Later on, both models give an identical ratio. 3ns FWHM pulse is peaked at 4.5 ns X-ray emission from laser-plasmas: recent results …

11. 100.0 mm 100.7 mm 101.4 mm 102.1 mm 103.4 mm f =10 cm 10 µm The experimental technique Tight-focus irradiation of solid target using clean (temporally and spatially) laser pulse • YLF oscillator, 1053 nm • Phosphate amplifiers • 3, 7, 20 ns, 2 beams • Single longitudinal mode • Intensity on target • up to: 5 1015 Wcm-2 High quality, near diffraction limited focal spot X-ray emission from laser-plasmas: recent results …

12. l 1 ns The X-ray spectra X-ray spectroscopy of K-shell emission from H-like and He-like Al ions X-ray spectra must be resolved in time to obtain the temporal evolution of H/He line ratios early during irradiation. An X-ray streak-camera is used. Raw data at low sweep speed X-ray emission from laser-plasmas: recent results …

13. Cross-calibration of spectra 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 X-ray emission from laser-plasmas: recent results …

14. EXPERIMENTAL RATIO vs TIME Lya to Heb intensity ratio from time-resolved X-ray spectra X-ray emission from laser-plasmas: recent results …

15. Evidence of transient ionisation Temporal evolution of Lya to Heb intensity ratio: Steady-State versus Time-dependent modelling Early during the emission, time dependent and steady-state model show different results. Later on, both models give identical ratio. 3ns FWHM pulse is peaked at 4.5 ns X-ray emission from laser-plasmas: recent results …

16. Evidence of transient ionisation Temporal evolution of Lya to Heb intensity ratio: Experiment versus SS/TD modelling Early during the emission, time dependent and steady-state model show different results. Later on, both models give identical ratio. Early stage experimental ratio agrees well with td calculations. 3ns FWHM pulse is peaked at 4.5 ns L.A.Gizzi et al., Letter on Phys. Plasmas, (2003); L.Labate et al; Phys. Plasmas (2005). X-ray emission from laser-plasmas: recent results …

17. Monochromatic µ-imaging with curved crystals Applications of LP X-ray sources:monochromatic µ-imaging …

18. X-ray Crystal Imaging Microscope *) “Image plane” at a distance q from the crystal given by the condition of equal vertican and horizontal magnification : Source on Rowland circle: Focusing condition:  *)Pikuz et al., Laser and Particle Beams,19:285, 2001 Sanchez del Rio et al., Review of Scientific Instr., 72:3291, 2001

19. Reflected Wavelengths R = 150 mm 0= 0.894 rad 2d = 19.9Å Horizontal plane Vertical plane a>a(R) a<a(R) a<a(R) a>a(R) y/mm x/mm Source on Rowland Circle: a = a(R) When the source is on the Rowland Circle, the reflected spectral range is minimum: the crystal behaves as a monochromator.

20. Ray-tracing simulations of X-ray µ-radiography#) X-ray Crystal Imaging Microscopy scheme XCIM (X-ray Crystal Imaging Microscope*) scheme allows monochromatic radiography of thin objects with µm resolution to be obtained XCIM scheme is based upon the use of a spherically bent crystal *) T.A. Pikuz et al., Laser Part. Beams 19,285 (2001); M. Sanchez del Rio et al., Rev. Sci. Instrum. 72, 3291 (2001) Ray-tracing simulations of the system with the ORTO ray-tracing code**): C++, fully object-oriented code arbitrary shapes and sizes of the source can be considered different forms of the crystal rocking curves can be taken into account typical running times: 5min for 5x106 sampled rays (Linux based P4) #)L.Labate et al., Ray-tracing simulation of an X-ray optics based upon a bent crystal for differential absorption applications, LPB, 2004.

21. Ray-tracing simulations: horizontal focus Spherical aberration and astigmatism: intensity distribution around the horizontal focus (without objects) X-ray intensity distribution at the image point using an Al plasma source and the crystal set to focus near the Hea line (no objects) Al Hea line Al IC line

22. Ray-tracing simulations: imaging a test object Ray-tracing of the XCIM scheme with Fresnel zone plate as a test object X-ray pattern at different crystal-detector distances

23. The X-ray source View: 45° from laser axis 15 µm laser spot on Cu target at 6E12 W/cm2 • THE DRIVING LASER • Nd:YAG oscillator • 6 ns pulse duration • 10 Hz rep rate • 1064, 532 nm • up to 500 mJ/pulse • up to 5 1013 W/cm2 on target • PC contr. Sync with target ≈25 µm FWHM source size

24. Monochromatic X-ray Beam from LP X-rays b) l0=7.748 Å c) l0=7.750 Å Lithium-like Central wavelength on crystal: IC He  1 a) l0=7.742 Å 0.5 0 Target: Al, Intensity on target: 2E13W/cm2 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)

25. Test image with XCIM configuration O Rowland circle 100 µm I1 « imaging » plane FH Object I2 S FV Image of a Frenel Zone plate with a monochromatic beam at 1.6 keV (Al He-a line) CCD Image 100 µm Image resolution: Contact image on X-ray film

26. Source Profile: Sample Profile:  Image profile: Space resolution condition:x = 2 1 0  Source characterisation using a zone-plate A Fresnel zone-plate with known geometrical properties is used as a sample to determine magnification and resolution properties of the imaging system X-ray image of a zone-plate: M=4.7 Resolution definitions using a step-function Radial line-out of image A 26 µm (FWHM) source size (PLX@ILIL) yelds a resolution of approx. 20µm at the object plane

27. DIFFERENTIAL ABSORPTION Difference in optical depth: I/I = 10-4  = (1506  10)cm2/g Detection Limit: =1.310-7g/cm2 An example: bromine and carbon Br C 1 2

28. DIFFERENTIAL ABSORPTION OF A TEST SAMPLE Incident beam 0.2 l of a0.265 g/ml solution of LiBr washer 1 l1 = 7.75 Å 0 1 1  substrate 0 Transmitted beamI1 =1210.5 cm2/g EXPECTED OPTICAL DEPTH DIFFERENCE Incident beam 1 l2 = 7.78 Å  t = -0.9±0.1 0 2 MEASURED OPTICAL DEPTH DIFFERENCE 1  0 Transmitted beam

29. ELEMENTAL 2D MAPPING Measurements on test-samples obtained from LiBr solutions with two different average concentrations P. Koester et al.., Quantitative analysis … submitted to Appl. Phys. B (2005).

30. ACCESSIBLE PHOTON ENERGIES Hydrogen-like Helium-like Element2p1/22p3/22p 3P12p 1P1 (eV) 13 Al1727.71729.01588.31598.4 14 Si2004.32006.11853.91865.1 15 P2301.72304.02140.32152.6 16 S2619.72622.72447.32460.8 17 Cl2958.52962.42775.12789.8 18 Ar3318332331243140 19 K3699370534933511 20 Ca4100410838833903 21 Sc4523453242954316 22 Ti4966497747274750 23 V5431544451805205 24 Cr5917593256555682 25 Mn6424644261516181 26 Fe6952697366686701 27 Co7502752672067242 28 Ni8073810277667806 29 Cu8666869983478392 30 Zn9281931889508999 31 Ga9917996095759628 Up to Z=22-23, He-a K-shell emission lines can be obtained using small 10 Hz Nd lasers. At higher Z, emission originate from L and M shells

31. Chlorine Copper Silicon Copper Calcium Titanium Alluminium Copper Moliben. “Tunability” of the PLX source

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

33. Sorgenti X ad impulsi ultracorti • Sorgenti K da Plasmi-Laser • Scattering Thomson[1] • X-ray Free Electron Laser[2] • Slicing (SR) Studi di fenomeni su scale temporali e spaziali atomiche • 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.

34. Sorgenti X da interazione laser-solido • Dimensione della regione di emissione paragonabile alla dimensione dello spot focale del laser[1]. • Durata dell’emissione Kparagonabile alla durata dell’impulso laser[2,3]. • Emissione isotropa. • Efficienza di conversione di energia laser in radiazione K 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.

35. BASIC MECHANISM: INNER SHELL TRANSITIONS K-a X-ray emission Ionised plasma X-ray emission Laser Laser heated plasma Fast electrons Fast electron heated solid 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).

36. Generazione di radiazione Ka • 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

37. Assorbimento risonante laser Onda di plasma densità critica 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.

38. Caratteristiche principali • 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 K è particolarmente efficiente per impulsi laser ultracorti [1]. • Efficienza di conversione di energia laser in radiazione K 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 K 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.

39. Experimental technique 10 Hz rep rate fs laser pulse Optical spectroscopy on reflected and diffused radiation

40. The femtosecond laser system

41. Ti:Sa oscillator pulse Gaussian fit Laser pulse width measurements photomultiplier • Zero-signal auto-correlator for high dynamic range measurement • Aimed at >106 peak-power to ASE contrast ratio BBO crystal Time scan The SH autocorrelator Laser M.Galimberti et al., IPCF-Report 2004

42. M.Galimberti et al., IPCF-Report 2004 Autocorrelator for ASE characterisation photomultiplier • Zero-signal auto-correlator for high dynamic range measurement • Aimed at >106 peak-power to ASE contrast ratio Amplified Pulse BBO crystal Gaussian fit Time scan Laser

43. Autocorrelator for ASE characterization(200 ps range) Measurement carried out by Amplitude Tech. using a SEQUOIA autocorrelator

44. Beam quality Profilo spaziale dell’impulso laser Piano equivalente con lente con focale di ca. 100 cm • 12 mJ • 67 fs •  15 m Intensità sul bersaglio fino a 1017 W/cm2 Spot focale di FWHM=15m per la lente di 14cm focale

45. 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). Hea hn Same spectral range, with femtosecond pulse and poor compression (≈10 ps pulse). Single-pixel noise arises from K-alpha photons and/or energetic electrons Ka(1486.70 eV) Hea hn

46. 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. 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

47. CCD Calibration set-up (<2 keV) 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 get a low photon flux (0.02 photons/pixel) collect a monochromatic beam onto the CCD sensor (dE/E ~ 5x10-2) Nd:YLF laser focusing lens PIN diode(*) Al filter crystal Al target The total crystal to CCD camera distance is about 1m in order to:

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

49. Calibration histograms 70 1320 eV 60 1550 eV 1140 eV 50 40 Counts 30 20 10 0 -10 20 40 60 80 100 120 140 ADC levels Response of CCD to monochromatic X-ray photons at low (<2keV) photon energy

50. CCD Calibration curve for SPS Calibration at higher (>2keV) energy was performed using radioactive sources