Abstract
We present a novel photonic Doppler velocimetry (PDV) design for laser-driven shock-wave experiments. This PDV design is intended to provide the capability of measuring the free-surface velocity of shocked opaque materials in the terapascal range. We present measurements of the free-surface velocity of gold for as long as ∼2 ns from the shock breakout, at pressures of up to ∼7 Mbar and a free-surface velocity of 7.3 km/s with an error of ∼1.5%. Such laboratory pressure conditions are achieved predominantly at high-intensity laser facilities where the only velocity diagnostic is usually line-imaging velocity interferometry for any reflector. However, that diagnostic is limited by the lower dynamic range of the streak camera (at a temporal resolution relevant to laser shock experiments) to measure the free-surface velocity of opaque materials up to pressures of only ∼1 Mbar. We expect the proposed PDV design to allow the free-surface velocity of opaque materials to be measured at much higher pressures.
Highlights
Photonic Doppler velocimetry (PDV) is intended for measuring the velocities of moving surfaces1 and is often used in studying the equation of state (EOS) of materials in dynamic experiments.2 photonic Doppler velocimetry (PDV) is usually used in the most common techniques for shockwave experiments, such as those based on guns3,4 and explosives,5 but it is seldom used with high-intensity laser experiments that can span the largest thermodynamic range and up to gigabar pressures.There are a few approaches for measuring the thermodynamic conditions of the target in shock-wave experiments. (1) Placing the target material on top of a standard material.6 The standard material is one that was previously calibrated and its EOS is known relatively well in the vicinity of the experimental conditions
Appendix for a comparison when using a 4-ns window), one data point between the start of consecutive windows, and 1500 bins] of the raw PDV signal is shown in Fig. 5(c), and the STFT of the normalized PDV signal is shown in Fig. 5(d), with the red line in each panel showing the obtained frequency profile by finding the maximum value within an ROI
The improvements to standard PDV allow the free-surface velocity of opaque materials to be measured in the terapascal pressure range
Summary
Photonic Doppler velocimetry (PDV) is intended for measuring the velocities of moving surfaces and is often used in studying the equation of state (EOS) of materials in dynamic experiments. PDV is usually used in the most common techniques for shockwave experiments, such as those based on guns and explosives, but it is seldom used with high-intensity laser experiments that can span the largest thermodynamic range and up to gigabar pressures.There are a few approaches for measuring the thermodynamic conditions of the target in shock-wave experiments. (1) Placing the target material on top of a standard material. The standard material is one that was previously calibrated and its EOS is known relatively well in the vicinity of the experimental conditions. Photonic Doppler velocimetry (PDV) is intended for measuring the velocities of moving surfaces and is often used in studying the equation of state (EOS) of materials in dynamic experiments.. There are a few approaches for measuring the thermodynamic conditions of the target in shock-wave experiments. By measuring the shock-wave velocity in the standard and target materials, the EOS of the target material can be extracted by using the impedance-mismatch technique and the reflected shock approximation (RSA). In this case, it is necessary to measure both the shock and particle velocities in the target material. It is customary to use the approximation ufs ≈ 2up, i.e., that the free-surface velocity is twice the particle velocity
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