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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:
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