We report the observation of a phase transition of diamond to denser than diamond carbon phase composed from 2 to 3 fullerene-type shells of onions. Raman spectra indicate the fullerene-type of the onions shells. The onions phase is a stable phase in a diamond instability zone of a phase diagram of carbon at pressure 70 GPa and temperature 2400 K. A mixture of diamond and Ni powders was heated by a laser beam under pressure in a diamond anvil cell. Both direct and catalytic diamond to onions transitions were observed during heating. The catalytic transformation includes the following steps. Melting of Ni during the laser heating at pressure 70 GPa, a 'diamond solution' (a transfer of carbon atoms from diamond) in liquid Ni and the formation of an equilibrium carbon phase from the supersaturated solution upon cooling. The catalytic process is a reverse one relative to the catalytic synthesis of diamond in a diamond stability zone at pressure around 6 GPa. The main result of our study is the presence of fullerene-type structures in the phase diagram of carbon in the region of diamond instability under high sub-Mbar pressure and wide range of temperatures.
In this paper, we demonstrate that combining a laser heating (LH) system with a tandem acousto-optical tunable filter (TAOTF) allows us to measure the temperature distribution (TD) across a laser-heated microscopic specimen. Spectral image processing is based on one-dimensional (1D) non-linear least squares fitting of the Planck radiation function. It is applied for determining the temperature T at each point (x, y) of the specimen surface. It is shown that spectral image processing using the 1D non-linear least squares fitting allows measurement of the TD of the laserheated microscopic specimen with higher precision and stability than those of the conventional linear least-squares fitting of the Wien approximation of Planck's law.Keywords: laser heating, diamond anvil cell, temperature measurement, acousto-optical tunable filter, spectral imaging.Citation: Bulatov KM, Mantrova YV, Bykov AA, Gaponov MI, Zinin PV, Machikhin AS, Troyan IA, Batshev VI, Kutuza IB. Multi-spectral image processing for the measurement of a spatial temperature distribution on the surface of a laser-heated microscopic object.
In this report, we demonstrate that combining the laser heating system in a diamond anvil cell (LH-DAC) with a tandem acoustic-optical tunable filter (LH-DAC-TAOTF) allows for the simultaneous measurement of (a) the relative infrared (IR, 1070 nm) power distribution on a specimen surface in the DAC; (b) the temperature distribution under laser heating of a specimen under high-pressure in a DAC; it also (c) provides an opportunity to control the shape of the IR laser spot on the surface of the heated specimen.The effect of the p-shaper on the shape and the position of the focus of the IR laser beam on a specimen using a TAOTF is also presented. For a 10Â long-working distance objective, the smallest diameter of the IR laser was found to be around 10 mm, when the focal plane coincides with that of the imaging optical system of LH-DAC. The highest diameter of the IR laser was shown to be 20 mm when the rim of the p-shaper was set at 3 mm. It is demonstrated also that the TAOFT not only permits to measure the two-dimensional (2-D) distribution of the IR laser power, but also allows for the alignment of the laser before each heating event at different pressures.
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