Compression, shock 240 - INDEX

Wise, J.L. and L.C. Chhabildas (1986), Laser Interferometer Measurements of Refractive Index in Shock-Compressed Materials, in Shock Waves in Condensed Matter (edited by Y.M. Gupta), Plenum, New York, pp. 441-454. 

The general character of the motion is shown in Fig. 1. A shock wave propagates in an unperturbed cold gas the maximum compression, which is dependent on the adiabatic index of the gas, is reached at the front of this wave. The velocity of propagation of the shock wave and the mass velocity at the front are related in an elementary way to the pressure of the shock wave. Behind the front the pressure, density, and velocity decrease.1... 

The required parameters in the calculation are Ushocked, t/s, and Wp. The shocked refi active index is given by the Gladstone-Dale equation nshocked=l+( -l)Pshocked/p, where p is the initial density of the PMMA (1.186 g/cm ) and n=1.487. Conservation of mass provides the shocked density pshocked=p/(l- Up / s) for a one-dimensional shock compression. Previous studies have validated the Gladstone-Dale model for shocked PMMA up to 22 GPa. [90-91]... 

These IR complex index component spectra were used to calculate the spectral effects that would be observed in a shock compression experiment. Figure 12 shows the time-dependent IR reflectance spectra calculated for normal incidence and p polarization in a 1 pm thick PMMA film during passage of the shockwave, assuming no pressure shift of the band frequencies. The uniaxial shock compression ratio fVE = l/(l-Up/us) was 1.5, as expected for... 

Analysis of the infrared spectra requires accounting for thin film interference effects, which, upon shock compression, change the composite reflectivity. To analyze the thin film interference effects, the infrared complex refractive index spectra for ambient samples of PVN, and the inert polymethylmethacrylate (PMMA), were determined as described in the section above. The only modification to the description above is the inclusion here of the dispersive rarefaction wave that releases the pressure [102]. 

After having travelled along a distance equal to several diameters of the tube, the compression waves join to form an incident shock wave, which looks like a discontinuity surface, of thickness of the order of a nanometre, separating the fresh reaction mixture (index 1) from the reaction mixture shocked by the incident wave (index 2). 

Batsanov SS, Dulepov EV, Moroz EM et al (1971) Effect of an explosion on a substtmce. Impact compression of rare-earth metal fluorides. Comb Expl Shock Waves 7 226-228 Tsay Y-F, Bendow B, Mitra SS (1973) Theory of temperature derivative of refractive-index in transparent crystals. Phys Rev B 8 2688-2696... 

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