second harmonic (sh) radiation from twined zno single nanorods (nr) in transmission geometry
DESCRIPTION
Second Harmonic (SH) Radiation from Twined ZnO Single Nanorods (NR) in Transmission Geometry. Presented by: Aaron Ricca Dr. S. W. Liu. Outline. Backround on SHG and ZnO Experimental Setup Experimental Procedure Results. Second Harmonic Generation (SHG) and ZnO. - PowerPoint PPT PresentationTRANSCRIPT
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