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N. Subramanian Now at IGCAR, India V . V. Struzhkin M . Somayazulu R . J. Hemley D. A. Dalton

Probing of materials with pulsed laser techniques in diamond anvil cells Alexander Goncharov Geophysical Laboratory, Carnegie Institution of Washington. Laser techniques. N. Subramanian Now at IGCAR, India V . V. Struzhkin M . Somayazulu R . J. Hemley D. A. Dalton S. R. McWilliams

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N. Subramanian Now at IGCAR, India V . V. Struzhkin M . Somayazulu R . J. Hemley D. A. Dalton

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  1. Probing of materials with pulsed laser techniques in diamond anvil cells Alexander Goncharov Geophysical Laboratory, Carnegie Institution of Washington Laser techniques N. Subramanian Now at IGCAR, India V. V. Struzhkin M. Somayazulu R. J. Hemley D. A. Dalton S. R. McWilliams M. Mahamood M. R. Armstrong J. C. Crowhurst V. Prakapenka I. Kantor M. Rivers Thrust Area 1: Metals under extreme environments Thrust Area 3: Hydrogen and hydrogen-bearing systems Grand Challenge 5:  How do we characterize and control matter away —especially very far away—from  equilibrium? Howard LLNL GSECARS

  2. Probing of materials with pulsed laser techniques under conditions of extreme pressures and temperatures • Outline: • Introduction to pulsed laser techniques for diamond anvil cells (DACs) • New laser techniques: • - pulsed laser heating • - time resolved X-ray diffraction combined with pulsed laser heating • - pulsed laser spectroscopy • - shock in DACs • Hydrogen at high P-T conditions • - (pulsed) Raman spectroscopy • - shock in DAC & ultrafast (ps) laser interferometry • Outlook DAC @ Omega (Rochester) DAC Jeanlozet al. 2007

  3. Reaching high-pressure and high-temperature conditions Phase diagram of hydrogen • Objective: • Bridge the gap between the conditions • of the shock and static experiments • Combine static and dynamic • experiments in the DAC gap Introducing: -pulsed laser heating -laser shock in the DAC Access to P-T conditions relevant for: -Planetary interiors -warm dense matter -new materials synthesis -fast chemical reactivity -melting curves

  4. Going Beyond Static Phase Diagrams Static phase diagram Introducing: -time resolved diagnostics -perform experiments in time domain both in single-shot and repetitive modes • Enabling studies of the phase transition chemical reaction kinetics: • Melt/solidification kinetics & growth • Solid-Solid phase transition kinetics & growth • Metastable phase growth • Detonation chemistry of explosives Time-dependent phase diagram Enabling access to metastablestates: This will generate new routes for synthesis of technological materials: Evans et al., 2006 Control matter out of equilibrium

  5. Raman spectroscopy in laser heated DAC:thermal radiation & chemical reactivity suppression Coupler Timing for pulsed heat + pulsed Raman operation: CW heat+ pulsed Raman T map: FE calculations Measurement CW heating: we discriminate thermal radiation spectrally (457 nm excitation), temporally (pulsed Raman, 532 nm) and spatially (spatial filter). Pulsed heating (ns and ms): we discriminate spatiallyand temporally (by measuring ~5-10 ms after the arrival of the heating pulse). A. F. Goncharov & J. Crowhurst (2005); Goncharov et al., 2008

  6. 1064, 532 nm mirrors Fianium Laser Wavelength: 1064 nm Rep Rate: Single Shot to MHz Energy: 2 μJ, Pulse Width: <10 ps Peak Power: ~20 kW We are developing a new coherent Antistokes Raman and broad band spectroscopy systems ½ WP Heating Laser μs scale pulse Short pass filter Spectrometer with Gated Detector (300nm-780 nm) Polarizer Delay Stage 532 nm notch filter 10 x DAC Objective 10 x Photonic Crystal Fiber Narrowband fundamental KTP Doubling crystal 532 nm notch filter Objective Broadband mirrors Broadband, chirped Source for CARS Long pass filter D. A. Dalton

  7. Broadband Optical Spectroscopy will enable single shot study of optical properties at the extreme environments attainable in the DAC. lens nonlinear fiber lens IR laser Supercontinuum Generation (SG) results in a very bright, white light source. The supercontinuum data was collected in a single shot manner at ~180 nJ/pulse into the fiber Tungsten lamp (~3000 K) data collected at 103 longer accumulation time. D. A. Dalton & S. McWilliams

  8. CARS ω532 ωCARS ωBB ω532 ωmolecule • Scientific Opportunities • Chemical reactions studied • on atomic level • Fast chemical kinetics • Transient products • Single-shot data

  9. X-ray diffraction combined with pulsed laser heating Spectrograph & Intensified gated CCD detector Pulsed fiber laser 1-50 μs, 5-20 KHz Laser Thermal radiation Pulse generator Sector 13: GSECARS X-ray Diffraction Time-resolved detector: Pilatus Goncharov, Struzhkin, Prakapenka, Kantor, Rivers

  10. Time-resolved x-ray diffraction at high pressure Pt, 60 GPa 2 μs 2 kHz 10k pulses ~3000 K RT Goncharov, Struzhkin, Prakapenka, Kantor, Rivers

  11. Pulsed laser heating in the DAC: s timescales Time-resolved X-ray diffraction Pulse profile vs Thermal expansion & temperature histories Detection of melting Tm Pt 38 GPa Pt GL: A. Goncharov, V. Struzhkin, A. Dalton; GSE CARS: V. Prakapenka, M. Rivers, I. Kantor

  12. Laser driven shock compression in the DAC: samples are dynamically compressed in the DAC Ultrafast interferometry diagnostics Schematic Shocked sample Diamond Moving Al surface Incident probe Pump Reflected probe Shock front Shocked Al • Precompression in 100 GPa range is possible • Preheating and precooling if needed • Ultrafast experiments can be small scale: • Table top system, unlike currently better known technique of laser shocks which involves large laser facilities (such as NIF) Precompressed sample Al Armstrong and Crowhurst, LLNL

  13. Chirped pulses allow us to apply a sustained pump to the sample and simultaneously acquire • Allow ablative, single shot excitation • >300 ps acquisition window with 2-3 ps time resolution

  14. Phase diagrams of hydrogen- multiple questions • Nature of the liquid above the melt line: bonding & ionization state • Melting line with a maximum? • Triple point at high • pressure? • Liquid ground state at very • high pressure? • Transition from molecular • to nonmolecular liquid- • abrupt vs continuous ? • Critical point at low • pressure? Phase diagram of hydrogen

  15. Raman spectra of vibron at high temperatures 60 GPa Finite element calculations “Hot” band New vibron “Solid” vibron Insulation Solid Fluid H2 Coupler • Strong T shift of the vibron • New lower-frequency vibron • Good approximation of the data assuming • Computed T map (Finite Element modeling) • Discontinuous vibron T shift Insulation Subramanian et al., submitted

  16. Temperature dependence of the Raman frequency Raman vibron frequency vs temperature Temperature measurements • Low-T: based on resistive heating measurements (Gregoryanz et al., 2003) • At high T: from the relative intensity of the side (hot) band • Pyrometry at high T agrees with “hot” band thermometry Subramanian et al., submitted

  17. Raman spectra of rotons and phonon at high temperatures Raman spectra at 300 K Raman spectra at 60 GPa • Roton (and coupled to them) phonon bands substantially decrease when the new low-frequency vibron appears at high T • Changes in the Raman spectra are very moderate at 300 K crystallization/ melting

  18. Time-Resolved Raman Spectra of Hydrogen with double-sided microsecond laser heating Sample: H2, Ir Coupler P = 10-25 GPa Timing before Raman excitation after Laser heating Raman spectra, 25 GPa Fluid Time-domain experiment S. R. McWilliams

  19. Phase diagram of hydrogen Phase diagram Vibron discontinuity • Fluid hydrogen changes bonding above 30 GPa evidenced from the observations of the new low-frequency vibron and substantial decrease of roton spectra at melting. • The melting line turns over above 110 GPa. The vibron discontinuity becomes less pronounced at these conditions. This may be related to the developing of short-range orientational order (Tamblyn & Bonev, 2010).

  20. Observation of Off-Hugoniot Shocked States with Ultrafast Time Resolution: Probing High-pressure, Low-temperature States Phase diagram of hydrogen Example of data for Ar Armstrong et al ., in press Bonev et al., (2010) Laser shocks in the DAC can generateand detect 10s GPa shock waves (and low pressure acoustic waves) in materials under precompression of 10s GPa

  21. First shots on deuterium Phase shift per 5 ps Delay (ps) • Shock and particle velocities of ~12-13 km/s and ~1 km/s for precompression ranging up to 36 GPa, giving a shock pressure ~10 GPa. • Possible phase transition over the duration of the probe window M. Armstrong. J. Crowhurst, LLNL

  22. Outlook • Pulsed laser techniques have a great abilities to: • access unavailable previously extreme P-T conditions • overcome problems of containing and probing chemically reactive and mobile materials • perform experiments in a time domain to access the time scale and dynamics of phase transitions & chemical reactions • The full potential of these techniques will be reached with further development of ultrafast (ps to fs) pump-probe techniques coupled to pulsed laser heating and laser shocks in the DAC.

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