Temperature measurements in a laser heated diamond anvil cell (DAC) are currently limited to temperatures above 1000 K using optics and detectors in the visible range. We have built a pyrometer in the IR range and expanded the lower limit of temperature detection to 400 K. The pyrometer is designed for very low thermal radiation intensities, measured sequentially through a set of bandpass filters in the range of 1.2-3.4 microm using very efficient IR photodetectors. The thermal radiation from the center of the cw Nd:YAG laser heated spot is least square fitted to a Planck curve, using a gray body approximation. Melting is detected by changes in the light scattering picture of an auxiliary He-Ne laser from the surface of the hot spot, and by a change in slope in the plot of hot spot temperature versus laser power. In this work we demonstrate measurement of the melting curve of zinc up to 25 GPa. The melting curve is in very good agreement with previous results which were taken up to 6 GPa in a large volume press.

CF₄ gas has a relatively high Raman cross section and a relatively small Raman shift and is an excellent candidate for a gas-filled hollow-core photonic bandgap (HC-PBG) fiber Raman wavelength converter. Here we investigate experimentally the onset and competition between stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) processes in high-pressure CF₄ gas. We focus 532 nm laser pulses into a high-pressure gas cell and measure the SBS and SRS response. The thresholds for both processes decrease with pressure, as expected. However, with short focusing geometries, the SBS threshold is lower than the SRS threshold, and with long focusing geometries, it is the opposite. We further show that with HC-PBG fiber geometry SRS dominates.

No abstract

No abstract

No abstract