Ultrafast measurement of the optical properties of aluminum during shock-wave breakout

We have used high-resolution frequency domain interferometry to make ultrafast measurements of shock-induced changes in the optical properties of thin aluminum targets. Measurements with an 800 nm probe wavelength found an unexpected phase shift during a 4.65 GPa shock breakout. Further measurements at 400 nm associate this phase shift with the pressure dependence of the 1.5 eV interband transition in aluminum. Data taken at several angles of incidence allowed the separation of optical from material motion effects, yielding an effective complex index for the shocked material.