Presented at

1
Vibrational Spectroscopy on Laser-Heated High
Density Fluids in Diamond Anvil Cell

• Presented at
• Laser Heating Workshop at the APS, March 20, 2004
• Choong-Shik Yoo
• Lawrence Livermore National Laboratory
• Livermore, California 94583
• (yoo1_at_llnl.gov (925) 422 - 5848)
• Collaborators
• Bruce Baer, Magnus Lipp, Alex Goncharov

2
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
3
Extreme materials research with laser-heated DAC
for synthesis
New opportunities for synthesis of exotic
materials !!!
Laser-heated DAC is capable of exploring a
delicate balance between mechanical (PDV) and
thermal (TDS) energies
4
Strong, coherently emitted CARS (Coherent
Anti-stokes Raman Spectroscopy) probes molecular
vibration in-situ at high P,T
5
Optical setup for CARS applied to laser-heated DAC
6
LLNL- CARS setup ready for studies of high
density fluids
7
CARS of laser-heated N2 at high pressures
8
Spontaneous Raman spectroscopy on laser-heated
materials at high pressures
9
Lasers with different mode structures enable to
heat selected areas in various configurations
Heating targets can be tailored into various
shapes such as flat foils, toroids,
micro-furnaces, steps, etc.
10
Discrimination of thermal radiation using both
spatial and spectral filters
Planck-fit to thermal emission
39 GPa 1861 K

• 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

11
Spontaneous Raman spectroscopy on laser-heated N2
at high pressures
The presence of n12 is evident for high
temperature, yet that of n1 indicates a large
temperature gradient near diamond surface
12
Thermal insulation of hot plate by Al2O3
13
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 lt2000K
• 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

14
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

15
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,

16
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
• Dx10mm at 50GPa DP2-5, DV12, DT2-5
• Unknown melt diagnostic, yet DT lt 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