dillon walker

Dillon Walker, Guangyao Li, Ken Singer

Hyper-Rayleigh Scattering

NSF Grant DMR-0850037

IntroductionFiber-optic cables in data transmission

(internet)Need to switch light quickly Nonlinear optical process

Introduction to Nonlinear OpticsNonlinear Effects in All MaterialsSelf-interaction of wave through matterNeed strong coherent light to observeLaser is only good light sourceMode-locked Ti:Sa used in my experiment

Hyper-Rayleigh ScatteringTechnique for measuring second term in

Third Order TensorRequires non-centrosymmetric moleculesFrequency doubles

NN

OO

O

SO

O

O

Chromo1

Hyper-Rayleigh Scattering

Material dissolved in solutionSolutions are symmetricSome incoherent scatteringCollected at 90 degreesVery weak signal

Multi-Photon Fluorescence

Photon energy may be absorbed by electronPhotons released as electron returns to ground

stateMay have same wavelength as Hyper-Rayleigh

400 600 8000.0

0.5

1.0

Ab

so

rb

an

ce

Wavelength (nm)

1

Fluorescence versus Hyper Rayleigh

Hyper Rayleigh Signal

Competing Multi-photon Fluorescence

Instantaneous

Non-Instantaneous

Single Photon Counting Technique

Fluorescence is not instantaneous

Time-Resolved Single Photon Counting can be used to distinguish between the two

Requires thousands of pulses for accuracy

Single-Photon Counting TechniqueSingle-Photon detectors have a dead time

after each photon detection.Can use sync to build a histogram of

photon detections after each pulseOnly works for low detection probabilities

2% Chromophore1 in Acetone

Setup

Photomultiplier

PC

Photo-detector

Sample

Beam-splitter

Titanium: Sapphire

Pump Laser