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Cross section from top to bottom through the middle of high pressure cell. 1: window assembly. 2: surrounding jacket. 3: cell body. 4: thermocouple assembly. 5: cell holder. 6: pressure in and out. The window assembly is explained in more detail in Fig. 3.
Cross section of high pressure cell through level of windows. Assignments as in Fig. 1. In addition 7: Connector for rupture disk. In the figure all windows are drawn in the physically correct positions, that is, opposite to each other in pairs.
Details of window assembly: The main idea of the cap is to have the cell tight even at very low pressures. Via the cap one can press the window slightly on to the extremely flat surface of the window support device. At high pressures then the construction seals itself through the action of the internal pressure. 1: supporting plug to held the window support device in place. 2: brass ring. 3: window support device. 4: teflon foil. 5: cap to press the window on 3. 6: o-ring. 7: optical window. 8: o-ring.
Sketch of setup including the possibility of performing backscattering experiments. The apertures of the high pressure cell are not in scale (exaggerated size). Alignment beam is necessary to define the optical axis for the tandem and defines the scattering center. Reference beam is needed for the internal stabilization of the tandem. MCA: multichannel analyzer to record the spectrum.
Measurement of the depolarization caused by the high pressure windows in transmission with crossed polarizers. The lower curve is the best obtained result and is in the order of . The two points in the upper part of the figure are obtained from fitting VH curves shown in Fig. 6 with a Lorentzian fit. The amplitude (of the Lorentzian contribution) of the TA phonon in the VH spectra compared to the TA phonon leads to the two values for the depolarization. These values have to be considered as typical and will be obtained if no special selection of the windows is performed. Nevertheless these values are already a factor of 2–3 times better than that which has been reported so far from other materials (Ref. 3).
Pressure variation of the transverse acoustic phonons in PPMS at . Data taken in VH geometry. Data with least TA phonon shift at , then . Data with largest phonon shift at . One can see the distortion of the spectra due to the appearance of the longitudinal acoustic phonons especially on the Stokes side of the high pressures at about .
Comparison of VH spectra taken at for PMPS with depolarization in the high pressure windows of about , upper curve and the best obtained depolarization from the windows in the order of , lower curve. Here no indication for a “leakage” of the VV longitudinal phonon can be seen. Upper curve shifted by a factor of 5 for reasons of clarity. Full lines are fits to the data, see text.
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