Second Harmonic (SH) Radiation from Twined ZnO Single Nanorods (NR) in Transmission Geometry.

Second Harmonic (SH) Radiation from Twined ZnO Single Nanorods (NR) in Transmission Geometry.

Presented by:Aaron Ricca

Dr. S. W. Liu

OutlineOutline

Backround on SHG and ZnO Experimental SetupExperimental ProcedureResults

Second Harmonic Generation (SHG) and ZnO

Second Harmonic Generation (SHG) and ZnO

It’s a nonlinear optical (NLO) process that, when discovered, started research in NLO materials

Photons pass through NLO material and constructively interfere to form a photon of twice the frequency, and energy, and half the wavelength

Much research done on ZnO in other areas because very stable, i.e. Peizoelectric and pyroelectric effects, UV and electron field emission, electrical conductivity… but not much in SGH of ZnO

Experimental SetupExperimental Setup

BF

2 KHz

/2

P

BS

M

BF

Ti:Sapphire

PMT

PC

Lock-in

LF

CHPMT

L

L

OB

S

FM Camera

BBO

CCD

Lock-in

Spectrometer

82 MHz,100fs

IR

The schematic of the experimental setup. PMT: photo-multiplier tube; CCD: charge coupled device cooled by liquid nitrogen; BBO: BBO nonlinear crystal; BS: beam splitter; LF: long-pass filter; BF: band-pass filter; CH: chopper operating at 2 KHz; /2: half-wave plate; P: Glan polarizer; L: lens; IR: iris diaphragm; OB: removable objective; M: mirror; FM: flipper mirror; PC: computer; S: sample.

BBO used to provide a reference to remove laser intensity fluctuations

Laser wavelength = 810 nm

Experimental SetupExperimental Setup

Finding the NanorodFinding the Nanorod

Extremely Difficult to locate, then re-locate if needed.

Record SGH via CamcorderRecord SGH via Camcorder

Flipper Mirror diverted beam into Camera and pictures were recorded

Sample and Beam GeometrySample and Beam Geometry

xo, yo, and zo are the crystallography coordinate axes of the hexagonal ZnO lattice with zo as polar direction

s, k, and z are the beam coordinate axes with s perpendicular to and k contained in the incidence plane

is the incidence angle, is the s- or p- polarized fundamental field, is the s- or p- polarized SH field

1,2,3 are three typical optical rays (dotted: fundamental rays; solid: SH rays), D is the diameter of the nanorod

Without the objective only directly transmitted SH ray 1 is recorded for polarization diagrams

NR: ZnO nanorod; FQ: fused quartz; Vac: vacuum

s

z

k

xozo

yo

D

1:Vac

2: FQ

3: NR

4: Vac

IR

Es

Ep

E2s

E2p

Ep

Es

z

ks

FQ

NR

FQ

2 1 3

2

13

NR

SH Images and Interference Fringes for Twined ZnO Single NR

SH Images and Interference Fringes for Twined ZnO Single NR

Enlarged images in insets show weak SH signal at center of nanorod

Instead of solid crystalline structure, actually 2 NR’s with 180˚ opposing domain structure (twins)

SHG can measure this where other methods fail

SEM Image for Typical Twin NR SEM Image for Typical Twin NR

Note separation between 2 halves of NR each with 180˚ different crystalline structure

Experimental ProcedureExperimental Procedure

Darken room and seal experimental setup in black cardboard enclosure

Run computer program that does the following:

Keep half-wave plate fixed and rotate polarizer while recording the light intensity after a small amount of rotation

Keep polarizer fixed and rotate half-wave plate while recording after a small amount of rotation

Run through procedure with and with out objective

Find new NR of different size in order to make sure data is consistent

Use new NR to repeat procedure again

Experimental ProcedureExperimental Procedure

Each run of data recording took about 25 minutes

Used a Z-cut quartz plate as a reference material in order to calibrate the system

Crystalline structure of the quartz was known and oriented along k axis

Susceptibility component, Fresnel transmission coefficient, and refractive indices of the quartz were all known and used when calculating the matrix of nonlinear susceptibility for SHG of ZnO NR

Calculation Geometry for Twined NR

Calculation Geometry for Twined NR

Simplified the twined NR to a dipole wire with a narrow gap for the purpose of modeling the twin interface

x'

y'

z'x

y

z

deff

dipolewire

imageplane

-L/2

L/2

Numerical Simulation for the z-component of the Time-Average Poynting Vector on the Image Plane

Numerical Simulation for the z-component of the Time-Average Poynting Vector on the Image Plane

Scattering patterned using Matlab

ReferencesReferences

S. W. Liu, H. Zhou, J. L. Weerasinghe, A. Ricca, R. Tian, Min Xiao; Second Harmonic Radiation and Far-Field Scattering Pattern from Twined ZnO Single Nanorods in Transmission Geometry

Amnon Yariv; Quantum Electronics Third Ed. 1989