HR: 13:55h
AN: MR13B-02    [Abstracts]
TI: New Micro-Raman Spectroscopy Systems for High-Temperature Studies in the Diamond Anvil Cell
AU: * Shim, S
EM: sangshim@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Lamm, R
EM: rlamm@MIT.EDU
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Rekhi, S
EM: srekhi@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Catalli, K
EM: krystle@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Santillan, J
EM: jsant@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Lundin, S
EM: slundin@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: In order to measure high-quality Raman spectra at high temperature and pressure in either the resistance- or laser-heated diamond-anvil cell, we have developed two Raman systems at MIT, a dispersive and a nanosecond time-resolved Raman spectroscopy systems. The excitation source of the dispersive Raman system is an Ar/Kr mixed ion laser which has nine available laser lines with wavelengths between 457 and 752 nm. Near UV laser lines allow us to measure Raman spectra up to 1200 K by shifting the spectral range of Raman modes away from intense thermal radiation. Near IR lines can be used for highly fluorescent materials. Three 500 mm spectrometers (Trivista spectrometer, Acton Research) are configured to operate in either single, triple subtractive, or triple additive mode combined with a liquid nitrogen cooled CCD detector. Holographic notch filters allow for high throughput in the single mode, which is ideal for weak Raman scattering. The subtractive triple mode allows detection of phonon modes to 5 cm-1 from the Raleigh line. The nanosecond time-resolved Raman system is designed for measurements above 1000 K. Previous studies at ambient pressure have shown that time-resolved Raman spectroscopy is the most effective technique to reject strong thermal radiation above 1000 K. We achieve nanosecond time resolution by synchronizing a frequency-doubled pulse Nd:YLF laser (527 nm, 0.1-10 kHz rep rate, 10-100 ns pulse width) with an intensified gated CCD detector (>5 ns gate width). This system is combined with a laser heating system (Nd:YLF laser, 1053 nm, TEM00, 45 W). Temperature is measured using both spectroradiometry and Raman thermometry methods. Our systems are designed to study phase relations and thermodynamic properties of mantle minerals at high P-T. Using these systems, we have measured the phase transition in (Mg_0.9Fe_0.1)SiO₃ pyroxene at 300-1700 K and 0 GPa, and the dehydration of serpentine at 2-8 GPa and 300-900 K. We also have found that the time-resolved Raman technique significantly suppresses the detection of the fluorescence of diamond anvils. For example, the secondary phonon mode to background intensity ratio of yellow diamond anvils improves by a factor of 2-5.
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005