Abstract
Laser compression has long been used as a method to study solids at high pressure. This is commonly achieved by sandwiching a sample between two diamond anvils and using a ramped laser pulse to slowly compress the sample, while keeping it cool enough to stay below the melt curve. We demonstrate a different approach, using a multilayer ‘ring-up’ target whereby laser-ablation pressure compresses Pb up to 150 GPa while keeping it solid, over two times as high in pressure than where it would shock melt on the Hugoniot. We find that the efficiency of this approach compares favourably with the commonly used diamond sandwich technique and could be important for new facilities located at XFELs and synchrotrons which often have higher repetition rate, lower energy lasers which limits the achievable pressures that can be reached.
Highlights
Laser compression has long been used as a method to study solids at high pressure
The standard method to perform these high pressure diffraction measurements on quasi-isentropically compressed material was developed by Rygg and coworkers[30], where they sandwiched a thin sample between two diamond anvils and used a ramped laser pulse to slowly compress the sample over several nanoseconds
X-ray Free Electron Lasers (XFELs) such the European XFEL and Linac Coherent Light Source (LCLS) II will be able to reach very high photon energies (> 20 keV)[39,41], which allows for much greater filtering to be used in front of detectors, reducing background caused by the ablation plasma from the drive laser and increasing signal-to-noise, as well as allowing a greater volume of reciprocal space to be explored
Summary
Laser compression has long been used as a method to study solids at high pressure. This is commonly achieved by sandwiching a sample between two diamond anvils and using a ramped laser pulse to slowly compress the sample, while keeping it cool enough to stay below the melt curve. To push the pressure beyond this point, while keeping the sample solid, ramp compression is required to keep the material closer to an isentrope These techniques are often paired with in situ X-ray diffraction which provides measurements of density and structure, and which has previously been proven in laser-shock experiments[6,10,11,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. Pb shock melts at the comparatively low pressure of ~ 50–60 GPa45,46 and we can readily test if we are generating off-Hugoniot states by observing diffraction from solid Pb well above this relatively low pressure
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