Laser Materials Under Impact Loading Temperature Measurement Research

Equation of state (EOS) is a focused field in the research of high energy density physics, important to understand thermodynamic properties of materials under extreme temperatures and pressures. Shock compression is one of the most common methods to create high energy density in laboratories. EOS is the relations among pressure, volume and temperature. In most of shock-wave experiments, the mechanical properties including shock pressure and velocity tend to be easily detected, however the thermal ones in which most concerned is shock temperature are difficult to be measured since the nature of temperature is complex and the requirements for measurements cannot be commonly satisfied.This thesis will present a robust way to measure the shock temperature by combining one optical pyrometer and VISAR. The pyrometer can detect the shock emission with10ps and1nm resolution, which are achieved by one spectrometer and one streak camera. This high resolution allows the pyrometer to record ultra-short changes in radiation. VISAR is used to measure the emissivity of shock radiation simultaneously with pyrometer. The emissivity can be calculated by comparing the energy change of the probing laser in VISAR when the probing laser reaches the shock front where the laser is absorbed and reflected. By combing the pyrometer and VISAR, we can obtain the emission and emissivity to infer a temperature.A grey body is assumed when we calculate the temperature. The emission is believed to be produced by shock front. Now the shock temperature can be obtained with the results of the pyrometer, VISAR and calibrations. Also we calculate the shock velocity by reading the transit time of shock through the step of target. Therefore, we get a relation between shock temperature and velocity which is invaluable to Hugoniot EOS.This thesis will show an example for utilizing this method inferring shock temperature. The rear side emission of Aluminum was measured. The shock breakout temperature obtained by the method shows a good agreement with SESAME Hugoniot temperature, which proves the method is effective. However, Al is opaque so that only when the shock reaches the rear surface emissions can be detected. Once the shock arrives, a rarefaction wave will be produced immediately (near1ps). Since the time resolution is10ps, the release plasma could affect the measurement of shock radiation. In this thesis, we assume that the absorption of plasma in10ps after shock breakout will be contained in the emissivity, which means that the absorption effect of plasma is considered and the method is still simple. The final result proves this assumption is reasonable.