In situ Raman spectroscopy with laser-heated diamond anvil cells

We have built a micro-optical spectroscopy system coupled with a Nd:YLF laser heating system for performing high pressure-temperature in situ Raman measurements in diamond anvil cells (DAC). A variety of materials can be investigated, providing information about structural and dynamical properties of condensed matter under extreme conditions. We report on a method for laser heating transparent samples using a metallic foil (Pt, Re, Mo, or W) as the infrared laser absorber (internal heating furnace) in the DAC. Metal foils of 5-15 micron in thickness with a small hole of 10-20 micron at the center are irradiated by the Nd:YLF laser beam directed into one side of the cell; the transparent sample in the small hole is uniformly heated and the Raman signals excited by an Arþ or Krþ laser are measured from the opposite side of the cell. The temperature of foil is measured by means of spectroradiometry, whereas the average temperature of sample is determined from the intensity ratios of Stokes/anti-Stokes pairs according to the principle of detailed balance. The average overall pairs give the sample temperature with the statistical accuracy of the Raman spectra, which is about plus/minus 50-100 K. Transparent samples such as CO2 have been heated up to 1600 K and 65 GPa, indicating the high efficiency of the internal metal furnace method. In situ Raman spectroscopy in the laser-heated DAC represents a powerful technique to characterize high P-T properties of materials including dense planetary gases and ices.