Optical Spectroscopy of Advanced Materials Jigang Wang

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


A brief history of optics A brief history of optics


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


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


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


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


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.


RefractionRefraction

Conventional Spectroscopy MethodsConventional Spectroscopy Methods


TT

RR

EE

- Absorption, Reflection, Emission, Interference, Scattering

- Spectrally resolved before or after sample


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


4−∝ λRamanI

Fourier Transform Infrared (FTIR) Fourier Transform Infrared (FTIR) Spectrometer Spectrometer


White light Interference

Nature can do similar tricks by itselfNature can do similar tricks by itself


Nature knows interferenceNature knows interference


The amazing light The amazing light –– LaserLaser


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)


Continuous beam:

Ultrashort pulse:

Continuous vs. ultrashort pulses of laserContinuous vs. ultrashort pulses of laser


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


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


Long vs. short pulses of laserLong vs. short pulses of laser

Long pulse

Short pulse


Generating short pulses = Generating short pulses = ““modemode--lockinglocking””Locking the phases of the laser frequencies yields an ultrashort pulse.


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


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


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.. .


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


Strategic advantagesStrategic advantages

Ultrafast

Ultrabroadband

Manipulation

e-


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


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


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


0.4

0.2

0.0

− ∆θ

K /θ

K

1 10 100 1000Time Delay (ps)

(1) (2) (4)(3)

Ultrafast demagnetizationUltrafast demagnetization


Cuprate SC: Generic Phase Diagram

R. A Kaindl et al., Science, 287, 470 (2000)

Ultrafast spectroscopy of Ultrafast spectroscopy of HTcHTc superconductorsuperconductor


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.. .

Optical Spectroscopy of Advanced Materials Jigang Wang

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