Laser heating properties

Experiments have established that there are four polymorphs in solid iron (a-, y-, S-, and s-phases). Saxena et al (1993) proposed a fifth iron phase (/3-phase) based on changes in thermal emission while laser heating the sample in a diamond-anvil cell. Boehler (1993) also observed similar changes in optical properties of iron in the same P-T range. Subsequent in situ X-ray diffraction measurements in the laser-heated diamond-anvil cell supported the occurrence of this new iron phase, although the structure of this phase is still under debate (Saxena et al, 1996 Yoo et al, 1996 Andrault et al, 1997, 2000 Saxena and Dubrovinsky, 2000). However, this phase was not observed in... 

A ruby laser pulsed irradiation of Ge/Si heterostructures with Ge nanoclusters (quantum dots) at the irradiation energy density near the melting threshold of Si surface has been studied by means of Raman spectroscopy and by numerical simulation of the laser-induced processes. Two types of the structures have been tested. They differ mainly in the depth of nanoclusters occurence (0.15 and 0.3 pm). From the RS analysis one may conclude that laser irradiation results in different changes of QD properties. The decrease of QD size dispersion is observed in the samples with QDs at 0.3 pm, this effect is not observed in the samples with QDs at 0.15 pm. The numerical simulation of laser heating shows that the QDs are in a molten state for the same time, but the induced temperatures of nanoclusters for the two depths differ by -100 K. This result indicates that qualitatively different effects of the laser irradiation may be connected with different temperatures of QDs during laser irradiation. 

Since part of the interpretations for the intermediate Fe in perovskite and postperovskite is based on the XES analyses for the total spin momentum of the 3d electronics in the samples, further understanding of the XES spectra involving multiple electronic transitions as well as theoretical calculations incorporating lattice distortion effects is needed to resolve the discrepancy between current experimental and theoretical results and interpretations. Although SMS spectra can now be collected from the laser-heated DAC experiments at relevant P-T conditions of the lower mantle, extended time windows are needed to extract more meaningful information to decipher the spin and valence states of iron in the lower-mantle minerals at relevant P-T conditions. Knowing the exact spin and valence states of iron in the lower-mantle minerals would then help geophysicists to address properties of the deep Earth. 

The critical temperatures of most metals can only be estimated and most lie well above those of mercury and the alkali metals (7. > 3000 K). Conventional measurements under static, equilibrium conditions are nearly impossible at such extreme temperatures and pressures. Transient methods such as shock waves, exploding wires, and laser heating have been developed to study at least a few properties of the high critical-point metals. These include the equation of state and the velocity of sound. But these techniques are less accurate than static measurements and it has not been possible to obtain measurements very close to the critical point, or indeed, even to determine with any reasonable level of precision the location of the critical points of most of the metallic elements. 

Table III summeuizes the creep properties, elastic moduli, electrical properties and retained strength properties of each experiment. The first laser-heated sample (ZMI-1) was uncoated and exposed to 1100°C at the CMC surface, with a recorded CMC backside temperature of 1034°C. The coated laser-heated sample (ZMI-2) was heated to a temperature of 1282 C at the EBC surface, and a temperature of 1010°C was maintained on the backside of the CMC substrate. It was assumed that if the CMC backside temperatures were equivalent, then the CMC surface temperatures should also be the same. Therefore the cooling air for the laser-based creep tests was...

High-pressure mineral physics therefore is concerned with the characterization of the physical properties and stability fields of planetary materials under extreme pressure and temperature conditions. For example, conditions present at the centre of the earth are thought to be in excess of 300 GPa and 5000 K. Such conditions can at present be obtained by laser-heated diamond anvil cells or multianvil presses. Emphasis of current in situ diffraction... 

Figure 13.10 Thermal heating properties of a 30nm spherical gold particle irradiated with 35 ps laser light at a 527nm wavelength and fluence of 1 mjcm f (a) Temperature profile...

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