ultrafast thz spectroscopy and nonlinear optical properties of semiconductor nanostructures zhen-yu...
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Ultrafast THz Spectroscopy Ultrafast THz Spectroscopy and Nonlinear Optical and Nonlinear Optical Properties of Semiconductor Properties of Semiconductor NanostructuresNanostructuresZhen-Yu ZHAOZhen-Yu ZHAO
17 July 2008
Laboratoire Pierre Aigrain - Ecole Normale Supérieure, Paris State Laboratory of Precise Spectroscopy - East China Normal
University, Shanghai
1
OutlinOutlinee
Section 2: Nonlinear Optical Properties of AgCl Nanocrystals doped Tellurite Nonlinear Optical Properties of AgCl Nanocrystals doped Tellurite
GlassesGlasses• FabricationFabrication• CharacterizationCharacterization• Nonlinear Optical MeasurementNonlinear Optical Measurement
Section 1: Development of THz Time Domain Spectroscopy (THz-TDS)Development of THz Time Domain Spectroscopy (THz-TDS) • Optical RectificationOptical Rectification• Micro-Photoconductive EmitterMicro-Photoconductive Emitter
Application of THz - TDSApplication of THz - TDS• Gain Measurement of Quantum Cascade Laser (QCL)Gain Measurement of Quantum Cascade Laser (QCL)
2
Section 1
Development & Application of Development & Application of THz Time Domain SpectroscopyTHz Time Domain Spectroscopy
3
THz THz RadiationRadiation
Section 1
1THz↔300μm↔1picosecond↔4.1meV↔10K
Application THz spectroscopy : Semiconductor nanostructuresApplication THz spectroscopy : Semiconductor nanostructures
http://www.thznetwork.org4
THz Time domain SpectroscopyTHz Time domain SpectroscopySection 1
Ti : sapphire laser
τ
BS
M2 M5
M1
M3 M4
Emitter
Electro-Optic Sampling
SZnTe
λ/4
WP
Balanced photodiodes
Probe beam
Pump beam
30 14
2THz
dn r E
Free Space Electro-Optic SamplingFree Space Electro-Optic Sampling
THz emitter:THz emitter:
Optical RectificationOptical Rectification
Photoconductive antennaPhotoconductive antenna
5
sinII-II 0
I
I
THz pulse
THz pulse
Δτ
Optical RectificationOptical Rectification
Laser pulse,Δτ :100fs, λ :800nm ZnTe
crystals
THz radiation
Z
Lens
SHG & Transmitted beam
2 IETHz
Section 1
6
-4 -2 0 2 4 6
(ps)
FFT
0 1 2 3 40.0
0.5
1.0
ET
Hz(
A.U
.)
THz
eVZnTeEg 35.2
Optical RectificationOptical RectificationSection 1
0,0
0,5
1,0
I THz (A
.U.)
0
1
2
3
I SH
G (m
W)
0 5 10 15 200,0
0,5
1,0
z (mm)
I Tra
ns (A
.U.)
7
Bolometer
PMT
Photodiode
Z
Z
Z
Teflon
Filter
Picarin Lens
Lens
Lens
8
Optical RectificationOptical RectificationSection 1
1. Optical Rectification 2. Second Harmonic Generation
3. Two Photon Absorption
4. Free Carrier Absorption
ħω 2ħω
ħω
ħω
Nonlinear Crystals Nonlinear Crystals
high state
low state
Conduction band
Valence band
2ħω
2Idz
dI
β: TPA coefficient
Nonlinear Optical ProcessesNonlinear Optical Processes
9
Optical RectificationOptical RectificationSection 1
0,0
0,5
1,00 60 120 180 240 300 360
0,0
0,5
1,0
0 60 120 180 240 300 3600,8
1,0
I TH
z (A
.U.)
I SH
G (
A.U
.)°
°
I Tra
ns (
A.U
.)
22 cos31sin f
f
21
θ
[001]
Laser polarization
ZnTe
X.-C. Zhang et al. J. Opt. Soc. Am. B 18 : 823 (2001)
fEdITHz40
214
D.C. Hutchings and B.S. Wherrett, J. Opt. Mod. 41: 1141 (1994)
Optical RectificationOptical Rectification
Lens :f=4cm
ZnTe
Rotation
Laser beam THz radiation
15mm
BBO
0 5 10 150,0
0,5
1,0
1,5 Z0
FCA
TPA
Expriment
z-2
TH
z in
tens
ity
z (mm)
-1211 cm 6)/ln(mm15 THzTHzTHz IIlz
Two Color ExperimentsTwo Color Experiments
Section 1
10
Interdigitated photoconductive Interdigitated photoconductive
antennaantenna Section 1
biasin
THz
UIJt
JE
11
Laser pulse,Δτ :100fs, λ :800nm
Hemisphere Si lens
+
—
eVGaAsEg 42.1
Conventional Photoconductive antenna
12
Interdigitated photoconductive Interdigitated photoconductive
antennaantenna
+-
Electrods
Opaques
A. Dreyhaupt et al. Appl. Phys. Lett. 86 :121114 (2005)A. Dreyhaupt et al. Opt. Lett. 31 :1546 (2006) Nathan Jukam, UCSB
stripline gap1.5µm
500µm
Interdigitated photoconductive Interdigitated photoconductive emitteremitter
Section 1
-1 0 1
ET
Hz (
A.U
.)
(fs)
Bias:20kv/cm Bias:40kv/cm Bias:60kv/cm Bias:80kv/cm Bias:160kv/cm
0 20 40 60 80 100 120 140 160 180
Bias field (kv/cm)
ET
Hz
(a.u
.)
THz intensity
0 1 2 3 40.0
0.5
1.0
ET
Hz(
a.u.
)
THz
Bias dependence
13
Interdigitated photoconductive Interdigitated photoconductive emitteremitter
Section 1
Γ→Γ→L Intervalley scatteringL Intervalley scattering
C. Ludwig and J. Kuhl, Appl. Phys. Lett. 69 (9), 1194 (1996)J.-H. Son, T. B. Norris, and J. F. Whitaker, J. Opt. Soc. Am. B 11, 2519 (1994)
14
Interdigitated photoconductive Interdigitated photoconductive emitteremitter
Optimization by change the exciting intensity
Section 1
15
0 1 2 3 4 50.0
0.5
1.0
E
TH
z (A
.U.)
THz
613 mW 215 mW 50 mW 10 mW
6 7 8 9-1,0
-0,5
0,0
0,5
1,0
ET
Hz (
A.U
.)
(ps)
10 mW 50 mW 215 mW 613 mW
Interdigitated photoconductive Interdigitated photoconductive emitteremitter
Space Charge Screenings Effect
Bias Field
Coulomb Field
Section 1
16
-
-
High Optical FluxLow Optical Flux
+ +— —
22p
ne
m
Interdigitated photoconductive Interdigitated photoconductive emitteremitter
Temperature Dependence of THz emitter
Section 1
17
dt
dneµEE lTHz
0 50 100 150 200 250 300
3,5
4,0
4,5
5,0
5,5
E
TH
z (A
.U.)
T(K)J. S.Blakemore, J. Appl. Phys. 53: R123-R181 (1982)
Section 1Comparison of 2 THz emittersComparison of 2 THz emittersZnTe Crystals Interdigitated Photoconductive
antenna
THz Amplitude 10V/cm 100V/cm
Central Frequency 2THz 1THz~~1.4THz
Bandwidth 0.5~~2.7THz 0~~3.5THz
S/N 500~1000 5000~~10000
18
0 1 2 3 40,0
0,5
1,0
ET
Hz (
A.U
.)
THz bandwidth
Antenna ZnTe
THz Quantum Cascade THz Quantum Cascade LaserLaser
Concept
1
2ħω
Interband transition Inter-subband transition
Semiconductor Laser Quantum Cascade Laser
Section 1
1970
First Idea
1980 1990 2000
First QCL @ Bell Labs THz QCL
Years1994 2002
Milestone
2.9 THz QCL 77k
2004
19
2006
1.9 THz QCL 95k
1971
THz Quantum Cascade THz Quantum Cascade LaserLaser
12 meV
300 200 100 0
50
100
Distance (nm)
17 meVMiniband
Miniband e-(1)
(2)
(1')
(g)
Section 1
Bound to Continuum Active-injection Region of 2.9THz QCL
20
21
THz Quantum Cascade THz Quantum Cascade LaserLaser
Section 1
Surface Plasmon Waveguide of 2.9 THz QCL
Active Region
Metal 220µm
SI Substrate
12µm
(a)
Bottomn+ layer
MetalContact
220µm
MPQ-Paris VII
THz Quantum Cascade THz Quantum Cascade LaserLaser
Section 1
V
QCL
Pyroelectric Detector
A
THz Collimation
THz
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,40,00
0,01
0,02
0,03
PT
Hz (
a.u.
)
I (A)
70K 65K 60K 55K 50K 40K 30K 20K 10K
Characterization of 2.9 THz QCL
22
THz Gain THz Gain MeasurementMeasurement
Ti : sapphire laser
τ
BS
M2 M5
M1
M3 M4
ETHz
FSEOS
SA B C
D
Probe beam
Pump beam
Zone Active
Section 1
23
THz Gain THz Gain MeasurementMeasurement
24 26 28 30 32 34 36 38 40
-40
-20
0
20
40
Ele
ctri
c fi
eld
(a.u
.)
Time (ps)
At threshold Below threshold
0 1 2 3 40,0
0,2
0,4
0,6
0,8
1,0
Frequency (THz)
Am
plitu
de (
a.u.
)
Amplified THz transmission by gain of quantum cascade laser
2.9THz
Section 1
24
THz Gain at different injection current THz Gain at different temperature
THz Gain THz Gain MeasurementMeasurement
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
1,0
1,5
2,0
2,5
3,0
90K
80K
70K
60K
50K40K
10K
Gai
n Fi
eld
Current (A)
0 20 40 60 80 1000,2
0,4
0,6
0,8
1,0
1,2
Cur
rent
(A
)
Temperature (K)
Section 1
Gain Clamping
25
26
Section 1
Summary 1Summary 1
Development of THz-TDS
THz performance of ZnTe crystal.
THz output of interdigitated photoconductive antenna
Application of THz-TDS
First measurement of Gain of 2.9 THz Quantum Cascade Laser
Section 2
Nonlinear Optical Properties of Nonlinear Optical Properties of AgCl NCs doped Tellurite GlassesAgCl NCs doped Tellurite Glasses
27
IntroductionIntroduction Section 2
28
Glass Χ(3) ~ 1014esu
SiO2 2.4
46PbO–42Bi2O3–12Ga2O3 42
20Nb2O5–80TeO2 72
------J. Lin et al. J. Non-Cryst. Solids 336 : 189–194 (2004)
Photonic Glasses
------Y.Q. LI et al. J. Rare Earth 25 : 412 – 415 (2007)
Er+ Doped TeO2-Nb2O5-ZnO Glass
Optical Switching Optical limiting
Nanocrystals doped Tellurite Glasses
Tellurite Glasses
FabricatioFabricationn
• Melting: 80TeO2:20Nb2O5 & 1%wt AgCl powder
800°C / 15minutes.
• Quenching: Annealed at 300°C
• Thermal treatment: At 360°C 30min, 60min, 90min, 120min
Section 2
29
CharacterizatioCharacterizationn
(a) 30min thermal treated (b) 60min thermal treated
Section 2
30
Nanocrystals FESEM Image vs Termal treatment time
CharacterizationCharacterization
(c) 90min thermal treated (d) 120min thermal treated
Section 2
31
Nanocrystals FESEM Image vs Termal treatment time
CharacterizationCharacterization
0
5
10
15
Num
ber
(A.U
.)
0 10 20 30 40 50 600
5
10
15
Num
ber
(A.U
.)
grain-size (nm)grain-size (nm)
0 10 20 30 40 50 60
12nm / 30 min
Section 2
32
Size distribution function vs thermal treatment time
26nm / 90 min
17nm / 60 min
35nm / 120 min
CharacterizationCharacterization
450 500 5500
100
200
300
400
500
600
Flu
ore
scen
ce In
ten
sity
(a.
u.)
Wavelength (nm)
undoped 0 min 120min
Cl-
Ag+
Jahn-Teller effect : Lattice deformation
Cl- colour center
Reaction: 2Cl- →Cl2 + 2e- & 2Ag++2e-→2Ag
400 500 600 700 800 900 10000,0
0,2
0,4
0,6
0,8
1,0
Abso
rbance
(a.u
.)
Wavelength (nm)
base glass 0min 30min 60min 90min 120min
Section 2
33H. Vogelsang, Phys. Rev. B 61: 1847-1852 (2000)
CharacterizationCharacterization
Eg
gm EhKT
exp
Urbach law:
Samples Eg (eV)
undoped 3.1
0 min 2.9
30 min 2.9
60 min 2.3
90 min 1.9
120 min 1.7Bandgap of glass matrix
Bandgap redshift of treated glass
Eg
Trapped state
Section 2
34
35
Nonlinear Optical PropertiesNonlinear Optical Properties Section 2
0 15 30 45 600
2
4
6
8
10
120min
90min
60min
30min
0min
Tra
nsm
itte
d P
ow
er
(J)
Incident Power (J)
No dopant50% BS
lens lens
SampleAttenutation
Powermeter
Powermeter
Nonlinear Optical PropertiesNonlinear Optical Properties
Lock-In
PCTi :sapphireLaser
M1
M2
L L LS D
Z
Open Aperture Z-scan
Section 2
-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5
0.85
0.90
0.95
1.00
T(z
)
Z (cm)
heating:120min heating:60min heating:0min Fitting curveβ: 1GW/cm ~~ 1.8 GW/cm
36
,2
320
gg
p
EF
En
EK
Nonlinear Optical PropertiesNonlinear Optical Properties Section 2
Lock-In
M1 M2
M3
M4
M5BS
Δτ
PC
L S
K1
K2
2K2-K1
2K1-K2 D
Ti :sapphireLaser
-400 -200 0 200 4000
10
20
30
DF
WM
sig
nal i
nten
sity
(A
.U.)
(fs)
glass 0min 30min 60min 90min 120min
Samples Eg (eV) n0 χ(3) (10-13esu) n2 (10-11esu)
undoped 3.1 2.0 7.2 1.2
0 min 2.9 2.1 7.3 1.3
30 min 2.6 2.2 7.8 1.4
60 min 2.3 2.2 14 2.3
90 min 1.9 2.2 11 1.9
120 min 1.7 2.2 9.5 1.6
DFWM experiment
37
38
Section 2SummarSummary 2y 2
Nonlinear optical properties of AgCl NCs doped tellurite glassNonlinear optical properties of AgCl NCs doped tellurite glass
•Samples were Prepared by Melt-Quenching and Thermal Treatment Methods
•Characterization with Microscopic and Spectroscopic Methods
•Nonlinear Optical Properties were Measured by Z-scan, Optical Limiting and DFWM
ConclusioConclusionn
39
Section 2: Nonlinear Optical Properties of AgCl Nanocrystals doped Tellurite GlassesNonlinear Optical Properties of AgCl Nanocrystals doped Tellurite Glasses• Fabrication• Optical limiting performance and Two-photon absorption• Enhancement of χ(3)
Section 1: Development of THz Time Domain Spectroscopy (THz-TDS)Development of THz Time Domain Spectroscopy (THz-TDS) • Competition OR TPA FCA, Azimuthal dependence• Intervally scattering, Space charging screening, Electron mobility Application of THz – TDSApplication of THz – TDS• Gain Measurement of 2.9THz QCL
AcknowledgementAcknowledgement
THz group (LPA-ENS)THz group (LPA-ENS)Advisor:Advisor: Jérôme TignonJérôme TignonStaff members:Staff members: Sophie Hameau, Sukhdeep Dhillon et al. Sophie Hameau, Sukhdeep Dhillon et al. Postdoc:Postdoc: Nathan Jukam; Nathan Jukam; Ph.D student:Ph.D student: Dimitri Oustinov;Dimitri Oustinov;Master student:Master student: Julien Amijo, Geog Dürr; Julien Amijo, Geog Dürr; Techniciens:Techniciens: Pascal Morfin, Phillipe Pace et al.Pascal Morfin, Phillipe Pace et al.Collaborators:Collaborators: Carlo Sirtori et al.Carlo Sirtori et al.
Sun’s Group (East China Normal University)Sun’s Group (East China Normal University)Co-Advisor: Co-Advisor: Zhenrong Sun, Zhenrong Sun, Staff members: Staff members: Tianqing Jia, Xiaohua Yang et al.Tianqing Jia, Xiaohua Yang et al.Collaborators:Collaborators: Jian Lin, et al.Jian Lin, et al.