Presented at Laser Heating Workshop at the APS, March 20, 2004

Choong-Shik Yoo

Lawrence Livermore National LaboratoryLivermore, California 94583

(yoo1@llnl.gov; (925) 422 - 5848)

CollaboratorsBruce Baer, Magnus Lipp, Alex Goncharov

Vibrational Spectroscopy on Laser-Heated Vibrational Spectroscopy on Laser-Heated High Density Fluids in Diamond Anvil CellHigh 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

10-50 GPa1000-5000 K

N2

CO2

CH2O

10-700 GPa

8000 K

Giant planets

H2, HeH2O, CH4, NH3

Extreme materials research with laser-heated DAC for synthesis

Laser-heated DAC is capable of exploring a delicate balance between mechanical (PV) and thermal (TS) energies

New opportunities for synthesis of exotic materials !!!

P- electron delocalization

Solid

MolecularAssociated

Molecularmetal

Ionization

Liquid

Extended

T-

ion

izat

ion

Kinetic line

Dissociation

P(GPa)

T (

K)

300

0

0

Atomicmetal

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 bandDye laser

Narrow bandDye laser

DAC

SPEC/CCD

Q/CW-YLF

CARS of laser-heated N2 at high pressures

During heating

Before heating

N2

W-toroid

100 m

-N2

300 K at 13 GPa

Fluid-N2

2300 K at 13 GPa

Spontaneous Raman spectroscopy on laser-heated materials at high pressures

DAC

Probe

Gasket

Sample

Hot plate

Laser Heating

Diamond Diamond cellcell

Fast spectrographFast spectrographradiometryradiometry

Tunable notch Tunable notch filtersfilters

Spatial filterSpatial filter

Dispersive Dispersive beamsplitterbeamsplitter

Fast spectrographFast spectrographRamanRaman

Laser heating Laser heating 1053 nm (YLF)1053 nm (YLF)

50 W50 W

Raman laser Raman laser 476 nm (Ar ion)476 nm (Ar ion)

CCD cameraCCD camera

Lasers with different mode structures enable to heat selected areas in various configurations

TEM01* YLF (Quantronix)

HeNe

HeNe TEM00 -YLF (Antares)

4xBEWP

PBS

Ar-Ion laser (Spec-Phys)

Iris

PMHRLM

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)

N2

Laser

Spatial filter

Intensity (a.u.)

800700600Wavelength (nm)

39 GPa1861 K

Planck-fit to thermal emission

80006000400020000

Wavenumber (cm-1

)

N2 at 20GPa &1700K

Ram

an in

ten

sity

N2 vibron

RubyDiamond Raman

Laser

Spontaneous Raman spectroscopy on laser-heated N2 at high pressures

24002350

Raman Shift (cm-1

)

1

12

31 GPa

26 GPa

20 GPa

1500 - 2000 K 2

The presence of12 is evident for high temperature, yet that of 1 indicates a large temperature gradient near diamond surface

Thermal insulation of hot plate by Al2O3

24002350

Raman Shift (cm-1

)

27 GPa

RT

~ 1820K

24002350

Raman Shift (cm-1

)

39 GPa

RT

~ 1700K

Probe

Laser Heating

Gasket

Sample

Hot donutAl2O3 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: CO2 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=10m at 50GPaP~2-5%, V~1~2%, T~2-5%- Unknown melt diagnostic, yet T < 10-20o (?)

• 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