optical spectroscopy of advanced...
TRANSCRIPT
Optical Spectroscopy of Advanced Materials
Basic optics, nonlinear and ultrafast optics
Jigang WangJigang Wang
Phys 590B Condensed Matter Physics: Experimental Methods
Department of Physics, Iowa State University and Ames Lab- USDoE
1. Feb 9th, 11th and 13th: overview, basic optics and spectroscopy
2. Feb 16th,18th and 20th: Advanced optics, ultrafast and nonlinear spectroscopy
- femtosecond lasers: case study; spectroscopy techniques: incoherent & coherent transient, magneto-optical, infrared & time-domain THz
General References: Demtroder, Laser Spectroscopy: Basic Concepts and Instrumentation
Diels and Rudolph (DR), Ultrashort Laser Pulse Phenomena
Shah, Ultrashort Spectroscopy of Semiconductors and Semiconductor Nanostructures
Chemla, D.S., Ultrafast Transient Nonlinear Optical Processes in Semiconductors
For example, see Copper, S.L, Optical Spectroscopy Studies of Metal-Insulator Transitions in Perovskite-related Oxides
Outline (Feb 9Outline (Feb 9thth --2020thth))
Jigang Wang, Feb, 2009
Today Today
Jigang Wang, Feb, 2009
Overview and Introduction
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
““Light is, in short, the most Light is, in short, the most refined form of matter.refined form of matter.””
Louis de Broglie
Berkeley, California
The first spectroscopy experimentThe first spectroscopy experiment
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
A brief history of optics A brief history of optics
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
17th-century 18th-century 19th-century 20th-century
Kepler,Huygens
….
Total internal reflection, Telescope, geometrical optics, the wave theory, prism dispersion, the particle theory of light
Newton… Fresnel, Young…
Interference, diffraction,expressions for reflected and transmitted waves,unified electricity and magnetism
MaxwellMichelson…
Einstein…
Light is (1) “a phenomenon of empty space”(2) both a wave and a particle
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
The equations of opticsThe equations of optics
/
0
BE E
t
EB B
t
∂ρ ε∂∂µε∂
∇ ⋅ = ∇× = −
∇ ⋅ = ∇× =
rr r r r
rr r r r
Maxwell’s equations
ε is the permittivity, µ is the permeability of the medium
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Solving MaxwellSolving Maxwell’’s equationss equations
22
20
EE
t
∂µε∂
∇ − =r
r( , ) cos( )E r t t k rω∝ ± ⋅
rr r r
Light is an Electromagnetic Wave
Wave Properties Wave Properties –– VelocityVelocity
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
2 2
2 20
E E
x t
∂ ∂µε∂ ∂
− =
1v
k
ωµε
= =Phase velocity
[ ] 1v /g dk dω −≡
v v / 1g phase
dn
n d
ωω
⎛ ⎞= +⎜ ⎟⎝ ⎠
Group velocity
Wave Properties Wave Properties –– SpectrumSpectrum
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
1 THz = 300 µm = 33 cm-1 = 4.1 meV
At an oblique angle, light can be completely transmitted or completely reflected.
"Total internal reflection" is the basis of optical fibers, a billion dollar industry.
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
RefractionRefraction
Conventional Spectroscopy MethodsConventional Spectroscopy Methods
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
TT
RR
EE
- Absorption, Reflection, Emission, Interference, Scattering
- Spectrally resolved before or after sample
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Absorption SpectroscopyAbsorption Spectroscopy
Visiblespectrum
Pen
etra
tion
dept
h in
to w
ater
Wavelength1 km 1 m 1 mm 1 µm 1 nm
UVX-ray
Radio Mic
row
ave
IR
1 mm
1 km
1 µm
1 m
Penetration depth into water vs. wavelength Dispersion elements
Scattering Spectroscopy Scattering Spectroscopy
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
4−∝ λRamanI
Fourier Transform Infrared (FTIR) Fourier Transform Infrared (FTIR) Spectrometer Spectrometer
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
White light Interference
Nature can do similar tricks by itselfNature can do similar tricks by itself
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Nature knows interferenceNature knows interference
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
The amazing light The amazing light –– LaserLaser
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
A laser will lase if the beam increases in irradiance during a round trip:that is, if I3 > I0.
Light amplification of stimulated emission of radiation (Laser)
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Continuous beam:
Ultrashort pulse:
Continuous vs. ultrashort pulses of laserContinuous vs. ultrashort pulses of laser
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
How fast is UltraHow fast is Ultra--fast?fast?
milli 10-3
micro 10-6
nano 10-9
pico 10-12
femto 10-15
atto 10-18
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
The evolution of pulse LasersThe evolution of pulse Lasers
1960 1970 1980 1990 2000
10–6
10–9
10–12
10–15
Tim
e re
solu
tion
(se
cond
s)
Year
Electronics
Optics
Courtesy of Trebino
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Long vs. short pulses of laserLong vs. short pulses of laser
Long pulse
Short pulse
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Generating short pulses = Generating short pulses = ““modemode--lockinglocking””Locking the phases of the laser frequencies yields an ultrashort pulse.
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
A generic ultrashortA generic ultrashort--pulse laserpulse laser
A generic ultrafast laser has a broadband gain medium,a pulse-shortening device, and two or more mirrors:
Pulse-shortening devices include:Saturable absorbersPhase modulatorsDispersion compensatorsOptical-Kerr media
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Different fquencies travel at different group velocities in materials, causing pulses to expand to highly "chirped" (frequency-swept) pulses.
Input ultrashort
pulse
Anymedium
Chirped outputnot-so-ultrashort
pulse
Ultrashort laser pulse broadeningUltrashort laser pulse broadening
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
UltraUltrafast Optics is Nonlinear Opticsfast Optics is Nonlinear Optics
Ultrashort & Ultrashort & UltrabroadbandUltrabroadband
1 10 100 10000
1
Spec
tral
Dens
ity
Photon Energy (meV)
HHG.. .
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
TimeTime
SignalSignal∆∆TT, , ∆α, ∆∆α, ∆RR
PL, FWM…PL, FWM…
∆∆tt = = --100 fs100 fs ∆∆tt = 0 fs= 0 fs ∆∆tt = 100 fs= 100 fs
λλ λλλλ
TT
RR
EE
Signals -> M, p, σ, χ(2) , χ(3) ...
Simultaneous high temporal and spectral resolution
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Strategic advantagesStrategic advantages
Ultrafast
Ultrabroadband
Manipulation
e-
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Ultrafast MagnetoUltrafast Magneto--optical Spectroscopy optical Spectroscopy
Magnetic IonsMagnetic Ions
CarriersCarriers
ExcitationExcitation
Detection Detection
©© J Wang, LBNLJ Wang, LBNL
kθ
kη
M
Highly sensitive to time reversal symmetry breaking
Tunable pump-probe from MIR, NIR to visible
Ultrafast THz SpectroscopyUltrafast THz Spectroscopy
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Amplitude Amplitude andand Phase informationPhase informationReal & Imaginary Part of Real & Imaginary Part of σσ((ωω), ), εε((ωω))
( ) ωωω σ ω
≡ ≈+ + 0
( ) 2( ) 1 ( )
OUT
IN S
Et
E n d Z
Complex transmission coefficientComplex transmission coefficient
( )tE t( )iE t
thin filmthin film
FieldField--resolved Detectionresolved Detection
-2 0 2 4 0 1 2 3
Electric field in time-domain FFT ⇒ spectrum
S/N~10000:1
Time delay (ps) Frequency (THz)
EO
Sig
nal
Pow
er S
pect
rum
≈ 0.5-3 THz
Coherent Transient SpectroscopyCoherent Transient Spectroscopy
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
k k’
k-q k’+ q
)(qV
)(int baH ↔
‘‘ResidualResidual’’ coulomb interactions coulomb interactions the dynamics between quasiparticlesthe dynamics between quasiparticles
k2
k3
k1
k1+k2- k3
Ultrafast FWM
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
0.4
0.2
0.0
− ∆θ
K /θ
K
1 10 100 1000Time Delay (ps)
(1) (2) (4)(3)
Ultrafast demagnetizationUltrafast demagnetization
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
Cuprate SC: Generic Phase Diagram
R. A Kaindl et al., Science, 287, 470 (2000)
Ultrafast spectroscopy of Ultrafast spectroscopy of HTcHTc superconductorsuperconductor
Jigang Wang, http://www.cmpgroup.ameslab.gov/ultrafast/
ManyMany--body Effects in SWCNbody Effects in SWCN
EEggOO
1D Band picture
van Hove van Hove singularitysingularity
OO
1D Exciton picture
EnergyEnergy
EnergyEnergy
eh
α
αOO
EnergyEnergy
α
120 160 200 240 280 320
0.0
0.5
1.0
120 160 200 240 280 320
Photon Energy (meV)
Tra
nsm
ittan
ce
0.0
0.5
1.0
(B)(A)
∆t = -500 fs-∆T
/T (
%)
200 fs
1000 fs
2000 fs
Photon Energy (meV)
Ultrafast Laser Lab TourUltrafast Laser Lab Tourwww.cmpgroup.ameslab.gov/ultrafast/
Pulse compressor
t
t
Solid state amplifiers
t
Dispersive delay linet
Short pulse
oscillator
1 10 100 10000
1
Spec
tral
Dens
ity
Photon Energy (meV)
HHG.. .