On-line Brillouin spectroscopy at GSECARSOn-line Brillouin spectroscopy at GSECARSVitali B. Prakapenka, Mark L. Rivers, Stephen R. Sutton, Alexei Kuznetsov - University of ChicagoJay Bass, Stanislav V. Sinogeikin *, Dmitry Lakshtanov – UIUC, * now at HP-CATBob Liebermann - COMPRES

Brillouin scattering Acoustic waves present in a solid due to thermal motion of atoms

Laser

O rig inalfrequency

Severa lfrequencies

Analyser

Frequency

O rig ina lB rillou insh ifted,Vp or Vs

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

Laserbeam IN

Scattered Light OUT

q

Vi = / 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 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

Brillouin spectroscopy

Shear: =V2S

Bulk: KS=V2P - 4/3 ,

Single-crystal: C11 = Vp2(100)

Rev. Sci. Instrum. 77, 103905 2006

laser

spectrometer

BS+XRD

)1( TKK TS

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

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, 103905 2006

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

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, 103905 2006

XRD and BS of polycrystalline NaCl at 35 GPa collected

simultaneously

NaCl Vs

NaCl Vp

NaCl Vp

NaCl Vs

Diamond Vs

Diamond Vs

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

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

High Temperature experiments

Temperature control(slow feedback)

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

MgOVp

MgOVp

MgOVs

MgOVs

ArBS

ArBS

ArVp

ArVp

XRD and BS of MgO in [100] direction in the DAC at 8 GPa and

~800 K

Ar pressure medium is melted collection time ~10 minutes

-15 -10 -5 0 5 10 150

50

100

150

200

250

Argon V

S

Inte

nsi

ty,

cts

Velocity, km/s

Argon V

P

Diamond

VS

Argon V

S

Argon V

P

Diamond

VS

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

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: