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On-line Brillouin spectroscopy at GSECARS

On-line Brillouin spectroscopy at GSECARS. Vitali B. Prakapenka, Mark L. Rivers, Stephen R. Sutton, Alexei Kuznetsov - University of Chicago Jay Bass, Stanislav V. Sinogeikin *, Dmitry Lakshtanov – UIUC, * now at HP-CAT Bob Liebermann - COMPRES. Brillouin scattering.

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On-line Brillouin spectroscopy at GSECARS

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  1. On-line Brillouin spectroscopy at GSECARS Vitali B. Prakapenka, Mark L. Rivers, Stephen R. Sutton, Alexei Kuznetsov - University of Chicago Jay Bass, Stanislav V. Sinogeikin *, Dmitry Lakshtanov – UIUC, * now at HP-CAT Bob Liebermann - COMPRES

  2. Brillouin scattering Acoustic waves present in a solid due to thermal motion of atoms Laser light interacts with phonons (or density / refractive index fluctuations) and is scattered with Doppler shifted frequency  In symmetric platelet geometry the Brillouin shift is directly proportional to acoustic velocity: Vi = / 2sin (*/2) S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  3. laser BS+XRD spectrometer Brillouin spectroscopy Advantages: • direct measurements of acoustic velocities • nondestructive optical spectroscopy • very small samples (down to 10-20 m) • from single crystal to non-crystalline materials • measurements at P-T conditions of the Lower Mantle Disadvantages: • complicated optical system • transparent and translucent samples • elastic moduli only for known density Shear: =V2S Bulk: KS=V2P - 4/3 , Single-crystal: C11 = Vp2(100) Rev. Sci. Instrum. 77, 103905 2006

  4. Why do we need Brillouin spectroscopy on-line? • measuring sound velocities and densities of materials simultaneously results in a pressure scale without reference marker and important materials properties (equations of state, elasticity, etc) as a function of pressure and temperature • the experimental data collected with XRD and BS at the same pressure-temperature conditions provide information essential for comparing with seismic observations and modelling the composition and evolution of the Earth • Brillouin spectroscopy combined with XRD open a new area of in-situ studies of materials at extreme conditions S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  5. Key design considerations: • should be flexible respect to the sample position andcompatible with x-ray diffraction technique • should be compact system due to limited space in the beamline station • should not interfere with other experimental techniques that are performed on the beamline (EXAFS, CMT, LVP) • should have reliable and quick alignment procedure • should have remote control option for data collection, adjustment and monitoring outside of hutch • should satisfy laser safety requirements due to using class-IV laser

  6. an elevated optical table • vertical scattering plane • movable along optical axis

  7. S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  8. Calibration Brillouin system with MgO single crystal starting with [100] direction at ambient conditions collection time is 5 minutes S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  9. EPICS control

  10. XRD and BS of single crystal MgO in [100] direction in the DAC at 4 GPa MEW MgO Vp MgO Vs S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka, Rev. Sci. Instrum. 77, 103905 2006

  11. XRD and BS of polycrystalline NaCl at 35 GPa collected simultaneously NaCl Vp NaCl Vp Diamond Vs Diamond Vs NaCl Vs NaCl Vs S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  12. High Temperature experiments S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  13. Temperature control(slow feedback) S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka, Rev. Sci. Instrum. 77, 103905 2006

  14. XRD and BS of MgO in [100] direction in the DAC at 8 GPa and ~800 K Ar BS Ar BS Ar Vp Ar Vp MgO Vp MgO Vp MgO Vs MgO Vs Ar pressure medium is melted collection time ~10 minutes

  15. In situ XRD and BS of argon at 60 GPa and ~700 K S. V. Sinogeikin, J. D. Bass, V.B. Prakapenka et al, Rev. Sci. Instrum. 77, 103905 2006

  16. Last year improvements: • Gear boxes (1:25) to improve accuracy of sample and laser beam positioning • Two horizontal translation stages for microscope alignment • Video switch system with multiple cameras (16) control using epics software, web compatible • Omega motorized rotation with water cooling for high temperature studies of single crystals

  17. User Program: • Open for proposals from anyone • Receiving ~4 proposals per beam-time cycle • 4 different groups have used the system

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