Ultrafast Thermal Melting in Nonequilibrium Warm Dense Copper

Area of Science:

• Condensed matter physics
• Materials science
• Plasma physics

Background:

• Understanding material behavior under extreme conditions is crucial.
• Warm dense matter (WDM) is an important state of matter relevant to astrophysics and inertial confinement fusion.
• Femtosecond laser-matter interactions provide a unique pathway to create and study WDM.

Purpose of the Study:

• To investigate the ultrafast dynamics of crystalline structure loss in laser-heated warm dense copper.
• To determine the characteristic timescale for the loss of periodicity.
• To explore the underlying physical mechanisms, such as thermal phase transitions.

Main Methods:

• Utilizing femtosecond laser heating to create warm dense copper.
• Employing X-ray absorption near-edge structures (XANES) spectroscopy just above the L3 edge for probing.
• Achieving picosecond (ps) resolution in X-ray absorption spectroscopy measurements.
• Performing two-temperature hydrodynamic simulations for data interpretation.

Main Results:

• Observed the loss of crystalline periodicity in warm dense copper.
• Determined a characteristic time of approximately 1 picosecond for this structural change.
• Identified this phenomenon within a specific energy density range of 1 to 5 MJ/kg.
• Found that experimental data were well reproduced by two-temperature hydrodynamic simulations.

Conclusions:

• The study confirms the ultrafast loss of crystalline periodicity in warm dense copper.
• The results support a thermal phase transition as the mechanism driving this structural change.
• The findings provide valuable insights into the dynamic behavior of materials under extreme conditions.