1. What experiments should we be doing? Dion L. Heinz University of Chicago

2. Physical Properties Thermal equation of state Melting (noted as important by CSEDI) Thermal conductivity Heat capacity, enthalpy of melting (really need to know optical absorption at experiment conditions) Optical properties of material at experimental conditions at laser wavelength(absorption) and over the wavelength range of the temperature measurements (emissivity).

3. Chemical Properties Phase diagram Multi-component phase equilibria Chemical diffusion Partitioning of major, minor and trace elements In other words petrology in the laser-heated diamond anvil cell

4. What do we need to do to accomplish these experiments? High stable laser power Stable sample temperatures Accurate temperature measurement Measurement of wavelength dependent optical properties Accurate pressure measurement Measurement of temperature gradients Control of temperature gradients Modulation of temperature as a function of time

5. What do we need to do to accomplish these experiments? High stable laser power (technology) Stable sample temperatures (technology, but can do today) Accurate temperature measurement (can do with below) Measurement of wavelength dependent optical properties (can do) Accurate pressure measurement (should be able to do) Measurement of temperature gradients (technology) Control of temperature gradients (technology, need excess laser power) Modulation of temperature as a function of time (can do now)

6. Inter-laboratory comparisons We need a fixed point scale of some sort that can be compared between laboratories for temperature and pressure measurement Andy Jephcoat’s suggestion of crossing melting curves is the best that I have heard of so far High P-T triple points in single component systems may also be a possiblity

7. Central to good inter-laboratory comparison Pressure scales Temperature calibration, with verification!

8. Why is temperature calibration and verification so important? Calibration removes system response Verification proves that the system works or that the physics of the system is correct Wavelength dependent emissivity is an important part of the verification procedure

9. Planck’s Radiation Law I ,T) =  ( )C 1 -5 [exp{C  / T - 1}] -1

10. What is the physical interpretation of emissivity? For the solid to give up a photon, there has to be a physical mechanism of that energy in the solid e.g. a vibration, electron, etc Metals typically have electrons that can give up the appropriate energy, but the emissivity can easily have a wavelength dependence

11. Emissivity Assume absorption is equal to emissivity (Kirchoff’s Law) Absorption is proportional to the complex part of the index of refraction (actually 4*pi/lambda)

12. Fe

14. Fe Emissivity In Iron the d electron band is right at the Fermi level, thus there are occupied electronic states below unoccupied states Therefore, as you go to shorter wavelengths of light, you can excite more and more electrons with photons

17. How much does emissivity matter?

18. What about transparent materials? Take MgO for instance, it does not have any mechanisms in the visible region to give up photons The band gap is large (i.e. in the UV) The lattice vibrations are in the infrared

19. MgO

20. SiO 2

21. Why does MgO glow? The answer has to be surface states (in a polycrystal), defects or impurities. The problem is what does the absorption spectrum of an impurity or defect look like? Impurities are also very sample dependent!

22. How do we measure the wavelength dependence of the absorption? Use three lasers to measure reflectivity or transmission of the sample in situ (you have to give up these wavelength bands for temperature determination) Some Problems with doing the above Reflectivity is highly surface dependent Transmission could be affected by scattering

23. Temperature gradients We calibrate our systems with a spatially flat source (in terms of intensity) What we need is a portable temperature gradient that can reproduce gradients at the scale of laser-heated diamond anvil hot spots

24. Conclustions I introduced the directions that I think we need to go in the next five years, and outlined where I think the rough spots are that need to be addressed to make progress