brillouin-light-scattering spectroscopykreisel/tr49/student_ss10/... · 2010. 8. 2. · benjamin...
TRANSCRIPT
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Brillouin-Light-Scattering Spectroscopy
Benjamin Jungfleisch
SFB/TR49 Student Seminar20th – 21th of July 2010
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Content
● Spin waves
● Brillouin Light Scattering (BLS)• Quantum mechanical picture• Conventional experimental setup
● Applications• Time-resolved BLS
• Phase-resolved BLS
• Wavevector-resolved
BLS● Summary
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Spin waves
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
)()(dt
MdM
MHM
dt
Md
s
Geff
×+×−= αγ
Spin waves
Textmasterformate durch Klicken bearbeitenZweite Ebene
● Dritte Ebene● Vierte Ebene
● Fünfte Ebene q
λ
Landau-Lifshitz and Gilbert equation
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
q
q
q
0H
0H
0H
dq ⋅||
Spin waves
Distinction between different energy contributions• Exchange energy
(generated by twist of neighbored spins, short range interaction)• Dipolar energy
(generated by magnetic poles in long-wavelength spin waves, long range interaction)
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Brillouin-Light-Scattering
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Inelastically scattered light
Brillouin-Light-Scattering
• Acoustic phonons
• Spin waves
Frequencies below ~ 500 GHz
Raman-Scattering• Optical phonons
• Molecule vibrations
Frequencies up to several THz
Tandem Fabry-Pérot interferometerGrating spectrometer
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Brillouin-Light-Scattering
Stokes: Anti-Stokes:
Energy conservation law: ωs = ωi - ω ωs = ωi + ω
Momentum conservation law: ks = ki - k ks = ki - k
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Fabry-Pérot interferometer (FPI)
The functionality of a Fabry-Pérot interferometer is based on multi-beam interference on two plane-parallel surfaces.
)cos(22 θλπϕ nl
=∆The phase difference:
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Fabry-Pérot interferometer
Transmittance and reflectivity
The transmittance function is given by:
where R is the reflectivity and is the coefficient of the finesse F.
Maximum transmission occurs when
m = 1,2,3,…
( ) ,2/sin1
1
)cos(21
)1(22
2
ϕϕ ∆+=
∆−+−=
FRR
RT
2)1(
4
R
RF
−=
,)cos(2 λθ mnl =
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Fabry-Pérot interferometer
θλ
λθλλ
cos2cos2
20
0
20
nlnl≈
+=∆
( )F/1arcsin2
πδλ
λ =∆=F
The free spectral range (FSR) is given by :
The finesse F is given by:
R
RF
−=≈
12
ππF
Our setup:F ≈ 110
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
RRRR
R
RR l
lc
ll
lc
ll
cl
∆≈∆+
∆=
∆+−=−=∆∆
λλλννν
1
11)(
Fabry-Pérot interferometer
Maximal transmission: 2
λml =
optical bandpassfreuquency measurement
∆+=∆R
R l
ll 1)( λλ
Linearrelation:
for lR= 0,3 mm: ∆ν= 500 GHz
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Operation of the TFPI
Possibility to suppress higher orders.
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Multi-pass tandem Fabry-Pérot interferometer (TFPI)
• High contrast: more than 1:1010• High spectral resolution in the Sub-GHz-Regime (up to 50 MHz)• Accessible frequency range: 0,2 GHz – 500 GHz
J. Sandercock, www.jrs-si.chH. Schultheiß, www.tfpdas.de
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
BLS setup
ActiveStabilization
+Positioning
• accuracy: better than 20 nm
• high reproducibility
TFPDAS 4 (www.tfpdas.de)by H. Schultheiss
Frequency Analysis
• frequency range:200 MHz – 1 THz
• spectral resolution:up to 50 MHz
Viewing System
• controlling sample position while measuring
Sample Stage
• optical resolution:up to 250 nm
• 2D scanning stage
λ
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Applications
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Applications
1) Time resolutionH. Schultheiss et al,J. Phys. D 41, 164017 (2008)
2) Phase resolutionA. A. Serga et al., APL 89, 063506 (2006)F. Fohr et al., RSI 80, 043903 (2009)
3) Wavevector resolutionC. Sandweg et al, Rev. Sci. Instrum. 81, 073902 (2010)
1)
2) 3)
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Applications:
Time-resolved BLS
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Time-resolved BLS
Study the decay of spin waves
and the dissipation processes
H. Schultheiss et al,J. Phys. D 41, 164017 (2008)
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Applications:
Phase-resolved BLS
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Superposition of the inelastic scattered light with a coherent reference beam with the same frequency.
Phase-resolved BLS
Inelastically scattered light contains phase information
22)(2 )()( AeAtxI ti =⋅=∝ +ϕω phase-information is lost!
But: BLS signal is proportional to laser intensity
Idea: interference!
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Example for phase-resolved BLS: Tunneling
running spin wave: wave has not reached the barrier yet
standing spin wave: wave is reflected back and forms a standing wave
YIG-film (1,6 x 7,7 mm)
barrier (cut, 20 μm)
Hext = 1846 OeνRF = 7,125 GHztpuls = 200 ns
standard position scan:
phase resolved scan:
λ/2
λ
T. Schneider: PhD Thesis
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Applications:
Wavevector-resolved BLS
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Wavevector-resolved BLS
No translational invariance in z direction
Only k|| = k sin(θ) conserved
Maximum wavevector: k < 2.10 5 cm-1(Backscattering geometry: ∆k = 2 k||)
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Wavevector-resolved BLS
Wavevector selection by rotating the sample
C. Sandweg et al, Rev. Sci. Instrum. 81, 073902 (2010)
Benjamin Jungfleisch SFB/TR49 Student Seminar 20th to 21th of July 2010
Summary
Brillouin light scattering
study spin waves…
…wavevector resolved
…time resolved
…phase resolved
…space resolved
…frequency resolved