time-correlated single photon counting (tcspc) scott thalman brigham young university advisor: dr....
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Time-Correlated Single Photon Counting (TCSPC)
Scott Thalman Brigham Young University
Advisor: Dr. John ColtonDr Haeyeon Yang USU Physics
Help from Mitch Jones, Steve Brown, Dallas Smith
Overview
Time-correlated single photon counting (TCSPC) measures photoluminescence (PL) lifetimes Pulsed laser illumination source Single-photon detectors Very fast timing module
100 picosecond time resolution with deconvolution
InGaAs Quantum Dots Optical properties are an indicator of
sample quality
Photoluminescence
e-
e-
e-
Excitation Relaxation
Ground State(valence band)
Excited States(conduction band)
PhotonEnergy Gap
e-
GaAs
Quantum Dots
Scanning tunneling micrograph of InGaAs
Quantum Dots on GaAs substrate
Dong Jun Kim et al 2008 Nanotechnology 19 47560
GaAs
QD
40 nm
InGaAs
Quantum Dots Confined electrons must occupy
energy states that fulfill the Schroedinger equation
Results:• Discrete energy
levels• Discrete
luminescence wavelengths
http://www.vectorsite.net/tpqm_02.html
En
erg
y
QD Photoluminescence
1000 1200 1400
1E-12
1E-11
1E-10
1E-9
P
ow
er
(Ab
itra
ry U
nits
)
Wavelength(nm)
120mW (889.5W/cm^2)180mW (1334.3W/cm^2)270mW (2001.5W/cm^2)
405mW (3002.2W/cm^2)
Sample 032607A, 3K, 780nm, .3s Tau, 8% Duty, Files 3-6, 2010-07-09
Time Correlated Single Photon Counting
QDSample
Pulsed Laser~30 fs, center wavelength 800 nm
Si-APDDetector
Fast Photodiod
e Detector
Ortec Fast DigitizerTiming Module
Start
Stop
60 70 80 90 100 110 120
10000
100000
Laser: 1.6 mW (Focus 3.5in in front of sample)25-30fs pulse 4.5 minCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width
File 314 Apr 2010 Haeyon Sample 032607-A
Cou
nts
Time (ns)
Lenses and Filters
QD Fluorescence Lifetime Expected
Results
Mazur et al 2006 Journal Of Applied Physics 100 054313
Fluorescence lifetime of InGaAs Quantum Dot (fig 1) and Quantum Well (fig 2) samples measured by a streak camera.
Fig 2Fig 1
70 75 80 85 90 95 100
1E-3
0.01
0.1
1
Laser: 9 mW approximately 0.2W/cm^225-30fs pulse 2 min 3.7 K 510K countsCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width
19 Apr 2010 All Samples Unfocused (normalized) Files 3-6
Cou
nts
Time (ns)
032607-B:t1= 1.56nst2= 3.7ns
032607-A:t1= 1.54nst2= 3.5ns
032907:t1= 1.77nst2= 3.7ns
IRF: t= 1.00ns
InGaAs QD Results
60 70 80 90 100 110 120
10000
100000
Laser: 1.6 mW (Focus 3.5in in front of sample)25-30fs pulse 4.5 minCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width
File 314 Apr 2010 Haeyon Sample 032607-A
Cou
nts
Time (ns)
Instrument Response
InGaAs QD Results:Convolution
( ) ( ) ( ) ( ) ( )f t g t h t f t g t t dt
Definition of Convolution
( ) ( ) 2 ( ) ( )FT f g FT h FT f FT g
Convolution Theorem
-4 -2 0 2 4 6 8 10
0.0
0.3
0.6
Apr 19 2010 Sample 032607-A (Focused) File 9
Data: g9_BModel: ExpDec1Equation: y = A1*exp(-x/t1) + y0Weighting: y No weighting Chi^2/DoF = 0.00004R^2 = 0.99916 y0 -0.00163 ±0.00177A1 0.74229 ±0.00585t1 0.64574 ±0.0106
No
rma
lize
d C
ou
nts
Time(ns)
0 10
0.0
0.3
0.6
0.9
No
rma
lize
d C
ou
nts
Time(ns)
DeconvolutionIRFMeasured Data
Example Of Deconvolution using Sample 032607-A File 9
Summary of Results
Sample Number
Photoluminescent Lifetime (ns)
Unfocused Laser
Focused Laser
032607-A 0.86 0.65
032607-B 0.78 0.78
032907 0.96 0.60
Conclusion
Using TCSPC we were able to measure the photoluminescent lifetimes of self-assembled InGas QDs to help determine their quality.
Our samples had lifetimes of 0.6-1.0 ns. Using deconvolution we were able to
enhance our results. Future studies will determine if
quantum structures such as QD chains can be formed by this growth method.Thank
You