| Research Abstract |
In this research, we investigate warm dense mater (WDM) physics which is located at the middle parameter range between condensed matter and plasmas. In this matter, atoms in high density matter is electronically excited and/or ionized. That means internal pressure in this matter is beyond Mbar and that number is the similar to the interia pressure in the large planets. Physically, there are difficulties to create the details model because both extrapolation from the condensed mater and plasma physics is failed. In the case of condensed matter model, the material condition is considered as sum of the ideal, well ordered wave-functions of atoms, but in WDM, some atoms excited electronically, some atoms keep the electron more tightly with bounded orbit. In plasma physics, the electron would be free from the individual ions, but in WDM, electrons are strongly affected by the nearest atom potential. In addition, the reason why in this parameter region, there are not good physical models is
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the lack of the precised experimental data. This is mainly caused from the difficulties in measurements of such short-live extreme conditions.
For overcome of these difficulties, we have developed ultra-short pulse white light probe and deep ultraviolet pump laser system to identify the optical properties of these transient condition. In this measurement, the WDM condition created with deep ultra-violet ultra-short pulse lasers is diagnosed with polarimater measurements of reflected light. To obtain full set of the Stokes parameters, the reflected light is divided into four different polarization component beams and observed with frequency resolved measurements system. The temporal structures are obtained with changing the delay of the arrival time of the probe beam. With this method, we identify when the transition occurs or how parameters are changed in time and space, and what is resonant frequency of this transient material.
To compare these measured data, we also construct new equation state model for this WDM. According to the comparison with Mercury behaviors, the strong interaction between each atom should be involved in this model. For example, to achieve the enough accurate curve of two-fluid region, we should include the cluster like formation of Hg atoms up to several tens of atoms. In addition, during these studies, we have found even with s and p orbit of electrons, the potential energy curves are crossed each other and the energy of 6p conditions, in some parameters, is lower than that of 6s. Finally, we find that it is necessary to include all these detail into the equation-of-state model in WDM to achieve the realistic reasonable properties. Less
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