Noisy Light SpectroscopyA science story

Darin J. UlnessDepartment of Chemistry

Concordia College, Moorhead, MN

Spectroscopy

Using light to gain information about matter

•Spectra•Transition frequencies•Time dynamics•Absorptivities•Susceptibilities

Information Uses of information•In Chemistry•In Biology•In Engineering

Modern Spectroscopy

Frequency Domain•Measure Spectra•Examples• IR, UV-VIS, Raman

•Material response• Spectrally narrow• Temporally slow

Time Domain•Response to light pulse•Examples• PE, transient abs.

•Material response• Spectrally broad• Temporally fast

Modern Spectroscopy

Frequency Domain•Measure Spectra•Examples• IR, UV-VIS, Raman

•Material response• Spectrally narrow• Temporally slow

Time Domain•Response to light pulse•Examples• PE, transient abs.

•Material response• Spectrally broad• Temporally fast

Time Domain Spectroscopy

Ultrashort pulses are used to excite a molecule

Time Domain Spectroscopy

Ultrashort pulses are used to excite a molecule

Creating Ultrashort Pulses

Fourier Transforms!• Things that happen fast in time require

a broad frequency spectrum• To make a short pulse you need a lot

of colors

Phase Locking

Synchronize the phase of the electric field• Many colors conspire to create a short

pulse• The phases of the different colors

need to be “locked”

Noisy light SpectroscopyUnlock the phase!• The phases of the different colors have

a random relation to one another• Many colors conspire to create a short

pulse coherence time

Ele

tric

Fie

ld S

tren

gth

Time

Noi

sy L

ight

Spe

ctru

m

Frequency

Noisy light SpectroscopyInteracting with molecules• The noisy light is “always on” …it is

quasi-continuous wave• The field may interact with the

molecule at any time

Foundations of Noisy Light

Optical coherence theory

Perturbation theory: Density operator

Noisy Light Spectroscopy

Nonlinear Spectroscopy

P= c ESignal

Material

Light field

Perturbation series approximation

P(t) = P(1) + P(2) + P(3) …

P(1) = c (1)E, P(2) = c (2)EE, P(3) = c (3)EEE

CARS

Coherent Anti-Stokes Raman Scattering

w1-w2= wR

wCARS= w1 +wRwR

w1

w1w2

wCARS

Bichromophoric Model

a

b

Noisy light

P(t)(3)

P(s)(3)*

< >

Theoretical Challenges

•Complicated Mathematics•Complicated Physical Interpretation

Difficulty•The cw nature requires all field action permutations. The light is always on.•The proper treatment of the noise cross-correlates chromophores.

New Viewpoint: The c(5) Story

Theoretical Challenges

•Complicated Mathematics•Complicated Physical Interpretation

Difficulty•The cw nature requires all field action permutations. The light is always on.•The proper treatment of the noise cross-correlates chromophores.

FTC Diagram Analysis

Set of intensity level terms

(pre-evaluated)

Set of evaluated intensity level

terms

Messy integration and algebra

Set of FTC diagrams

ConstructionRules

EvaluationRules

Physicshard hard

easy

FTC Diagram Analysis

a

b

P(t,{ti})

P(s,{si})

arrow segments: t-dependent correlation

line segments: t-independent

correlation

I(2)CARS

Monochromator

NarrowbandSource

BroadbandSource

Lens

Sample

Interferometer

t

B

B’

MI(2)CARS

ComputerCCD

•Signal is dispersed onto the CCD

•Entire Spectrum is taken at each delay

•2D data set: the Spectrogram

I(2)CARS: Data Processing

18000 18100 18200 18300 18400

-2

-1

0

1

2

BenzeneT22

0 200 400 600 800 1000 1200

0

25

50

75

100

125

150

BenzeneT22

100 200 300 400

0.2

0.4

0.6

0.8

Fourier

Transformation

X-Marginal

I(2)CARS: Hydrogen Bonding

17300 17400 17500 17600

-400

-200

0

200

400

Pyridine

17300 17400 17500 17600

-400

-200

0

200

400

Pyridine

17300 17400 17500 17600

-400

-200

0

200

400

ave x.45 pyr_water

FT

NeatPyridine

Pyridine/Water Xw= 0.55

I(2)CARS: Hydrogen Bonding

I(2)CARS: Halogen BondingPyridine and C3F7I

0

0.5

1

1.5

2

2.5

3

3.5

4

900 920 940 960 980 1000 1020 1040 1060 1080 1100

Frequency (cm-1)

Norma

lized In

tensity

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Neat

C6F13I and Pyridine

0

0.5

1

1.5

2

2.5

3

3.5

4

900 920 940 960 980 1000 1020 1040 1060 1080 1100Frequency (cm-1)

Norma

lized In

tesity

Neat

0.1

0.2

0.3

0.4

0.5

0.6

0.7

.8

0.9

Halogen Bonding

Electropositves-hole

Test Charge

Electroneutral“ring”

Electronegative“belt”

Photosynthesis

AcknowledgementsStudentsTheoryJahan DawlatyDan BiebighauserJohn GregioreDuffy TurnerKurt HaagIssac HeathCarena Daniels

Other Group MembersDr. Mark Gealy, Department of PhysicsDr. Eric Booth, Post-doctoral researcherDr. Haiyan Fan, Post-doctoral researcher

FundingNSF CAREER Grant CHE-0341087Henry Dreyfus Teacher/Scholar programConcordia Chemistry Research Fund

Method DevelopmentPye Phyo AungTanner SchulzLindsay WeiselKrista CosertPerrie ColeAlex HarshBritt BergerZach JohnsonThao Ta

Hydrogen/Halogen bondingEric BergJeff EliasonDiane MolivaJason OlsonScott FlancherDanny Green

PhotosynthesisBecca HendricksonMeghan KnudtzonDylan HowieBobby Spoja