Single shot measurements of laser driven shock waves using ultrafast dynamic ellipsometry

Abstract

Ultrafast dynamic ellipsometry, a diagnostic that measures both the shock-induced optical effects and the motion of shocked materials, has been implemented in a single shot form. This is accomplished using chirped pulse interferometry and probing the sample at two angles with both s- and p-polarized light. The application of single shot ultrafast dynamic ellipsometry should prove important in future studies of shocked transparent materials and metals because it allows concurrent determination of the initial and shocked optical constants, shock and particle velocities, and the picosecond time dependence of these properties with a higher signal-to-noise ratio and less stringent sample requirements than multishot methods. The ability to infer both the initial and shocked refractive indices of the material eliminates the need for performing extra experiments to calibrate the window, greatly simplifying the analysis and making each shot a self-contained experiment. The implementation of this diagnostic is described, and its utility is demonstrated on a shocked thin film of polycarbonate. Analysis of the data employs a multilayer thin film model to calculate the reflectance as a function of the time-dependent layer thicknesses and optical properties. Hugoniot data for the thin film polycarbonate is presented along with the effect of shock compression on the refractive index, which is consistent with the Gladstone-Dale relation.

The elastic-plastic response of aluminum films to ultrafast laser-generated shocks

“…Details of the technique used for the free surface measurements were published by Bolme et al 15 and details for the spectral shaping of the shock drive pulse were published by McGrane et al 16 For these experiments, the laser was focused through the glass to an ϳ100 m spot at the aluminum film to generate the shock. Since the energy of the drive pulse was Gaussian shaped across the spatial dimension, we present data from an approximately 5 m spatial region in the center of the shock, where the shock was traveling normal to the surface of the aluminum.…”

Shock compression of reactive powder mixtures

“…82 One notable exception is ultrafast dynamic ellipsometry (UDE), which can deduce the time-resolved motion of the shock front in thin-films. 83 The utility of this method, however, is limited to samples transparent to the diagnostic wavelength. It remains a challenge to monitor the evolution of mechanical/thermal/chemical state ahead and behind the shock front within an opaque material at the mesoscopic level.…”

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

“…Through this technique, the decay of both plane [4,7] and convergent [9,10] shocks with pressures exceeding tens of GPa have been reported. The propagation of shock waves in soft transparent materials such as polycarbonate and PMMA has been observed by single-shot ultrafast dynamic ellipsometry [11,12], a method allowing the separation of pressureinduced variations in elastic and optical properties. In such materials, characteristic pressures ranged from a few to 10-20 GPa, and acoustic Mach numbers defined as M A ¼ u=v 0 , where u is the particle velocity and v 0 the linear acoustic velocity, were subsonic in the range 0.2 < M A < 0.9.…”