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

Advantages:  direct measurements of acoustic velocities  nondestructive optical spectroscopy  very small samples (down to  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 Brillouin spectroscopy Shear:  =  V 2 S Bulk: K S =  V 2 P - 4/3 , Single-crystal: C 11 =  V p 2 (100) Rev. Sci. Instrum. 77, laser spectrometer BS+XRD

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,

should be flexible respect to the sample position and compatible 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 Key design considerations:

 an elevated optical table  vertical scattering plane  movable along optical axis

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

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,

EPICS control

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

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

High Temperature experiments

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

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

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,

 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 Last year improvements:

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