Laser-driven intense X-rays : Studies at RRCAT

Transcription

1 Laser-driven intense X-rays : Studies at RRCAT B. S. Rao Laser Plasma Division Team Effort Principal contributors : Experiment: P. D. Gupta, P. A. Naik, J. A. Chakera, A. Moorti, V. Arora, H. Singhal, U. Chakravarty Electronics: C. P. Navathe, M. S. Ansari, Bupinder Singh Mechanical: S. R. Kumbhare, R. P. Kushwaha, S. Sebastin Laser support: R. A. Khan, R. K. Bhat Collaborators: K. Nakajima (KEK, Japan), R. A. Ganeev (IE, Uzbekistan)

2 Outline Description of TW laser Introduction to laser driven X ray sources Studies at RRCAT X ray diagnostics Soft X rays by Higher Harmonic Generation Bremsstrahlung hard adx rays K α X ray generation X ray enhancement in water window region X ray sources based on laser wake field acceleration Conclusions

3 Table-top terawatt laser at LPD Chirped Pulse Amplification Oscillator : Titanium sapphire Total energy gain ~ 10 9 Mode-locking Stretch factor ~ λ 0 =790 nm / Δλ=60 nm / τ pulse ~ 12 fs E L ~ nj, Pulse rep. rate = 76 MHz Transmission ~ 60% Laser beam to target area Laser beam line Laser parameters after compression : Band width : 20 nm Pulse duration : 45 fs Max. Peak Power : 10 TW Max. rep rate ` : 10 Hz Focusable intensity ~ W/cm 2

4 Studies on intense laser-matter interaction Laser interaction with Solid : Gas jet : Fast electron Laser-driven electron acceleration (100 MeV) Kα X-rays Capillary plasma : Bremsstrahlung radiation Laser-driven electron acceleration (GeV) Neutron generation Plasma plume : Ion acceleration Higher order harmonic generation Experimental area Interaction Experimental setup chamber Laser beam line Lead shielding

5 Laser-driven particle and radiation source Flow of energy Characteristics Table-top Femtosecond duration Micrometer size Collimated Bright Synchronized

6 Generation of relativistic electrons Laser-solid interactions ti : Charge ~ few nano-coulombs Energy ~ few MeV (depends on intensity) Energy spread ~ 100% Divergence ege ~10 0 Direction of emission depends on interaction parameters Laser-gas interaction : Depending on acceleration mechanism Charge ~ 100 pc to few nc Energy ~ 100s MeV Energy spread < 10% to 100% Divergence < few mrad to 100 mrad Emitted in the direction of the laser

7 X-ray spectroscopic diagnostics Parameter Regimes : Sub kev to MeV photon energy range Resolution : few ev to few tens of kev Desirable Features : Quantitative measurements On-line processing Simple to operate

8 X-ray diagnostics developed in-house On-line high resolution x-ray imaging crystal spectrograph (λ=5-12 Å, Δλ=0.012Å ) Transmission grating XUV spectrograph (λ=3-90 Å, Δλ=0.6Å) Flat field grazing incidence XUV spectrograph (λ= Å, Δλ=0.5Å ) XUV imaging spectrograph (λ=5-160 Å, Δλ=2 Å, Δx 25 μm) Sodium iodide based hard x-ray spectrograph (150 kv kev 1.5 MV) MeV)

9 X-ray dispersion-less spectrograph Single photon detection technique : Large number of pixels in a CCD chip, a few laser shots (ideally one) are required to get an x-ray spectrum in a large energy interval, with a typical resolution well below 5 % in the energy range from 1 kev to a few tens of kev. Typical CCD frame X-ray spectrum 400 Copper tensity (a.u.) X-ray In Energy (kev) Histogram of the pixel count gives the incident x-ray spectrum. Incident photon energy was determined from the calibration curve

10 HHG from Plasma Plumes Main pulse parameters E = 120 mj τ = 45 fs I = W/cm 2 I = W/cm 2 HHG upto 73 rd order was observed in Mn 33 rd 73 rd Enhanced 13 th H (In plume) H. Singhal et al., Phys. Rev. A 79, (2009)

11 Laser-solid solid target interactions (Bremsstrahlung hard X-rays) I L 1.3 x W/cm 2, τ 45 fs X-ray angular distribution hν > 40 kev Two sources of X-ray radiation : - One at the target - The other at the glass window of the plasma chamber Glass window x-ray e e Cu target x-ray e The second source gives rise to observed anisotropic distribution Laser B. S. Rao et al., J. Appl. Phys. 102, (2007)

12 Laser-solid solid target interaction (Fast Electrons) Ti: sa laser Electron energy spectrum 30 סּ B = 1 kg Dipole magnet Cu 25 S-Pol P-Pol DRZ Phosphor electrons Image of energy dispersed electrons S(E)dN/dE [a a.u.] MeV Energy (MeV) Observed 3/2 ω radiation (Two plasmon decay) Long scale length plasma due to pre-pulse Resonance n absorption of laser light Jet of fast electrons along target normal (Landau damping / wave-breaking)

13 Laser-solid solid target interaction (Ultrashort intense K-α x-rays) 500 X-ray Inten nsity (a.u.) Copper Energy (kev) Mg K-a = 4 x 10 8 photons / Sr Ti K-a = 3 x 10 9 photons / Sr Cu K-a = 1.8 X 10 9 photons / Sr Conversion efficiency: ~ 10 4 %

14 Time-resolved X-ray Diffraction Experimental layout X-ray spectrum of Laser produced titanium plasma High intensity laser provides a high pressure : Lattice deformation Change of the x-ray reflectivity and shift of rocking curve on a subpicosecond time scale. Collaborative experiments with UGC-DAE Consortium for Scientific Research, Indore

15 Laser-nanofiber target interaction (X-ray enhancement in water window region) CNFs of 60 nm average diameter r nm CNF CNFs of 160 nm diameter average (different magnification) Solid graphite x-ray int tensity (a.u) nm CNF Graphite 10 0 Polythelene Wavelength (A) Enhancement w.r.t graphite target 160 nm CNF 3 60 nm CNF 18 Enhancement w.r.t. polyethylene targett Graphite nm CNF nm CNF 45

16 Experiments on laser-gas interactions Laser and target t characterization ti Focal spot = 10 μm Supersonic nozzle (orifice: mm 2 ) 1.2 mm Important diagnostics for electron beam ICT Phosphor +CCD Permanent dipole magnet (B eff =4.6 kg) Self-focusing was observed through side imaging of Thomson scattering the laser light

17 Laser wake-field acceleration Experimental setup Inside interaction chamber Laser beam Electron beam I L = 1.8 x Wcm -2 Vacuum ~ 10-5 mbar ICT Laser pulse length is few times λ p and laser power is higher than critical power for relativistic self-focusing Investigations : Electron beam divergence Energy spectrum Beam charge Dependence on plasma density Effect of laser chirp Effect of f/#

18 Results of the electron acceleration experiment (Using F/10 off-axis parabola, I L ~ 1.8 x W/cm 2 ) For n e >5x10 19 cm -3, e-beam was produced in each laser shot with total charge > 2 nc Charge Vs Pressure Charge Vs Chirp Spatial profile n e = 6 x10 19 cm -3 Beam quality was sensitive to the plasma density (n e ) Low divergence (< 10mrad) at n e ~8.5x cm -3 B. S. Rao et al., IEEE Trans. Plasma Sci. 36, 1694 (2008) Incre easing intensit ty n e = 8.5 x10 19 cm -3 Collimated beam

19 Energy of the electron beam Mono-energetic electron beam was produced at a plasma density of 8.5 x cm -3 Divergence (θ) : ~ 4 7 mrad Peak current ~ 1 ka Energy spread (ΔE/E ) : ~ 4 8 % Transverse emittance Geometric : ~ π mm.mrad Normalized : ~ π mm.mrad B.S. Rao et al., New J. Phys (to appear)

20 Increase in energy of the electron beam (Using F/7.5 Off-axis parabola) 10 mrad Laser intensity ns ty =2.4x10 18 W/cm 2 Mono-energetic electron at lower density ~ 6.5x10 19 cm -3 Increased acceleration length Collimated beam produced at 40 bar Beam parameters : Divergence : 3 6 mrad Energy : MeV Highly collimated beam occurs in ~ 50 % of the shots. 20

21 Laser-triggered Capillary Discharge Plasma for high energy acceleration Current: Single shot Current: Ten shots 160 A 160 A 50 ns V = 20 kv E L = 50 mj 50 ns V = 20 kv E L = 50 mj Plexi glass capillary Length : 70mm, Diameter : 500μm Peak discharge current : ~ 500 A, Time of peak current : ~ ns Jitter : < 10 ns Experiments to test optical guiding of high intensity laser pulses are to begin shortly.

22 GeV acceleration with 100 TW laser Two stage all optical model

23 γ-ray generation for radiography Advantages: low divergence, point-like electron source γ-ray y source : Size ~ few hundreds microns High resolution radiography of dense objects Glinec et al., PRL 94, (2005)

24 Ultrashort X-rays from laser undulator ( Inverse Compton scattering ) Relativistic e - -beam Laser Scattered light Undulator radiation: λ L 2 λ = u 2 2 K 1+ + γ θ 2 2γ 2 Inverse Compton scattering: λ L = λ 4γγ laser 2 a γ 2 θ 2 obs. θ emission, rms ~ γ 1 N laser Numbers: ( hω 1.5 ev ) L T = 10MeV γ 20 hω 2.4 kev el

25 Ultrashort X-rays from laser undulator (Proposed experimental set-up) Scattered photon energy = 60 kev Single photon counting mode Peak Brightness ~ ph/s/mm 2 /mrad 2 /0.1% BW10 8 Photons/shot Avg. Brightness ~ 10 8 ph/s/mm 2 /mrad 2 /0.1% BW10 8 Photons/shot

26 Concept and properties of the source Ultrashort X-rays from plasma undulator ( Betatron t radiation ) Laser Plasma channel 10 µm KeV X-ray Beam 30 fs, 50 TW Accelerated electrons 500 µm Betatron oscillations Peak photon energy : E (ev) = γ 2 n e (cm 3 ) r 0 (µm) Source Properties - up to 10 6 photons/shot/0.1% BW mrad divergence. - Broadband spectrum kev - Source size <5 µm - Femtosecond

27 Conclusions X-ray spectroscopic diagnostics covering spectral range from sub kev to MeV have been developed. d Studies on laser driven ultrafast x-ray sources Progress on laser-driven electron acceleration Future plans on generation of high brightness x-ray sources based on laser wake-field accelerated electron beams are discussed Applications of the bright ultrafast x ray source are Applications of the bright ultrafast x-ray source are foreseen within the frame of national and international collaborations.

28 Thank You!