Presented at Laser Heating Workshop at the APS, March 20, 2004 Choong-Shik Yoo Lawrence Livermore National Laboratory Livermore, California (925) Collaborators Bruce Baer, Magnus Lipp, Alex Goncharov Vibrational Spectroscopy on Laser-Heated High Density Fluids in Diamond Anvil Cell

Laser-heated DAC creates the P,T conditions of energetic detonation and Giant planetary interiors Structures and stabilities of simple molecules are not known at high P,T GPa K N 2 CO 2 C H 2 O GPa 8000 K Giant planets H 2, He H 2 O, CH 4, NH 3

Extreme materials research with laser- heated DAC for synthesis Laser-heated DAC is capable of exploring a delicate balance between mechanical (P  V) and thermal (T  S) energies New opportunities for synthesis of exotic materials !!! P- electron delocalization Solid Molecular Associated Molecular metal Ionization Liquid Extended T- ionization Kinetic line Dissociation P(GPa) T (K) Atomic metal 100 Strong disparity in bonding results in a huge kinetic barrier (metastability)

Strong, coherently emitted CARS ( Coherent Anti-stokes Raman Spectroscopy ) probes molecular vibration in-situ at high P,T

Optical setup for CARS applied to laser-heated DAC

LLNL- CARS setup ready for studies of high density fluids ML,QS- Nd:Yag Broad band Dye laser Narrow band Dye laser DAC SPEC/CCD Q/CW-YLF

CARS of laser-heated N 2 at high pressures During heating Before heating N2N2 W-toroid 100  m  -N K at 13 GPa Fluid-N K at 13 GPa

Spontaneous Raman spectroscopy on laser-heated materials at high pressures DAC Probe Gasket Sample Hot plate Laser Heating Diamond cell Fast spectrograph radiometry Tunable notch filters Spatial filter Dispersivebeamsplitter Fast spectrograph Raman Laser heating 1053 nm (YLF) 50 W Raman laser 476 nm (Ar ion) CCD camera

Lasers with different mode structures enable to heat selected areas in various configurations TEM 01* YLF (Quantronix) HeNe TEM 00 -YLF (Antares) 4x BE WP PBS Ar-Ion laser (Spec-Phys) Iris PM HRLM dual coated Heating targets can be tailored into various shapes such as flat foils, toroids, micro-furnaces, steps, etc.

Discrimination of thermal radiation using both spatial and spectral filters Spatial filtering to eliminate thermal radiation from hot donut Raman notch spectral filter to minimize straight laser light Use “blue” excitation to reduce thermal radiation ~ 100  m Hot donut (W) N2N2 Laser Spatial filter 39 GPa 1861 K Planck-fit to thermal emission N 2 at 20GPa &1700K Raman intensity N 2 vibron Ruby Diamond Raman Laser

Spontaneous Raman spectroscopy on laser-heated N 2 at high pressures GPa 26 GPa 20 GPa K 2 The presence of  12 is evident for high temperature, yet that of 1 indicates a large temperature gradient near diamond surface

Thermal insulation of hot plate by Al 2 O 3 27 GPa RT ~ 1820K 39 GPa RT ~ 1700K Probe Laser Heating Gasket Sample Hot donut Al 2 O 3 matrix

Challenges in vibrational spectroscopy on laser-heated materials Sample preparation: Micro-fabrication of heat absorber Thermal insulation of hot plate and sample from diamond Highly reactive high density fluids Laser-heating: Uniform heating of hot plate and sample In-situ pressure measurements Spontaneous Raman: Weak signal Limited to low emissivity materials and relatively low T <2000K Alternative routes: deep “blue”, pulse Raman, coherent Raman CARS: Optical transparency of sample Diamond damage Materials application: Complex chemistry with multiple path ways Difficulties in characterization: structure, order, (meta-)stability, etc

What are the most important experiments? Melting and phase diagram studies above 100GPa: -Melting vs. recrystallization, amorphorization vs. phase transitions vs. diffusive motions -Melt probes: speckle pattern, reflectivity, laser power, etc. Structural studies: -Ordered systems: polycrystals, single crystals, mixtures and alloys -Disordered systems: liquid, amorphous, glass Novel materials applications: -Superhard, HEDM, optical, high-Tc, etc. Mechanical properties: -Materials strength, elastic properties, plastic deformation, -Microstructures, textures, preferred orientation

What are the most important experiments? X-ray spectroscopy: elastic and inelastic -Interatomic potentials, molecular configuration, electronic structure -X-ray induced chemistry: ionization, excite state fluorescence, Real-time structural studies: -Thermodynamic(stability) vs. kinetic(metastability) -Reology and dynamics -Transport properties: thermal diffusion, viscosity, Associated technology developments: -In-situ diagnostics for intrinsic material properties: X-ray, Raman, CARS, reflectivity -In-situ P,T probes: pyrometer, calibrated thermocouple, X-ray induced fluorescence -Internal P,T standard materials -New DAC cells: Membrane-DAC, Large volume DAC, Dynamic DAC, etc. -Laser-heating: CO 2 heating, short pulse heating, -Sample fabrication: Micro-furnace, insulation,

What should the guiding philosophy be? Time constraints: -Simple and easy in operation: -Optimized alignment and calibration procedures Compatibility: -DAC in different types -Software: x-ray and laser-heating operation -Hardware: not too many computers, remote & manual controller, visual aids, fibers Balanced approach:  x=10  m at 50GPa  P~2-5%,  V~1~2%,  T~2-5% -Unknown melt diagnostic, yet  T < o (?) Practicality: -Experimental geometry: axial and radial x-ray experiments -Integrated experiments: laser-heating with ADXD, Raman, IXS, etc. Operational principles: -It is an x-ray experiment, not laser-heating -24-hr operation: minimize downtime for laser alignment and sample preparation -Mentor/Buddy system: any first-time user should team up with an expert