2007/ 7/ 9

ERL研究会「コンパクトERLが拓く世界」
KEK, Tsukuba

テラヘルツ時間領域分光法と基礎科学への応用

Department of Physics, Kyoto University
Koichiro Tanaka
SCOPE project
2003-2007

JSPS project
2006-2010

ATT OC
Advanced Terahertz Technologies
adapted for Optical Communication

Exploitation of Organic Electronic Materials
of Potential Dynamic Switches for Nonequilibrium Condensed Matter Sciences

1

講演内容
• テラヘルツテクノロジーとは何か？
• 時間領域テラヘルツ分光法の基礎• 時間領域テラヘルツ分光法による物性測定
有機材料, 強誘電体、半導体、超伝導体
水、水溶液• 非線型テラヘルツ分光の必要性と戦略

Kyoto University 20062

Importance of terahertz frequency region
Radio wave

THz region Light wave

Dielectric constants

Intermolecular vibration
Large molecule vibration

Molecular
Vibration

Electronic Transition

Rotation

ε1 Relaxation mode
X-rayXdiffraction

線回折Spin excitation

ε201m

100mm

10mm

1mm

100μm

10μm

1μm

Wavelength

Radio wave

100nm

10nm

1nm

0.1nm

VisibleInfrared
Kyoto University 2006

3Absorption of Liquid Water
Microwave cooker
Frequency (THz)
8910101010111012101310101410151610610THz

5-1

Absorption Coefficient (cm )10410310210110010-110-210-3MWEWIRVis. UV

10-41010m

1m100mm 10mm

1mm

100μm 10μm

1μm

100nm 10nm

Wavelength

Jackson, Classical Electrodynamics

4yx

B. B. Hu and M. C. Nuss, Opt. Lett. 20, 1716 (1995)

THz

THz

THz-Imaging

Kawase (Nagoya/Riken), Nikon

5

講演内容
• テラヘルツテクノロジーとは何か？
• 時間領域テラヘルツ分光法の基礎• 時間領域テラヘルツ分光法による物性測定
有機材料, 強誘電体、半導体、超伝導体
水、水溶液• 非線型テラヘルツ分光の必要性と戦略

Kyoto University 20066

THz-TDSの進展 - フェムト秒レーザーの進歩
Photoconductor Si SI-GaAs

a-Si

LT-GaAsfemtosecond laser

RD-SOSwith Battery(IMRA)103

Mode-locked Nd:glass laser
YAG laser
Flashlamp
PC antennadye laser
E-O sampling

Free space
E-O sampling

103

102

CW mode-locked
dye laser

Self-mode locked
Ti : Sapphire laser

102

10

Wavelength (μm)

Pulse Width (fsec)

104

CPM ring dye laser
第３世代フェムト秒システム

10PulseComplession

1965

1975

1

Year

Diode laser + 希土類

..

1985

Er ファイバーレーザー
Yb glass laser

1995

2005
Kyoto University 20067

THz-detection
Generation

Detection
Photocurrent
Bias

LT-GaAsA

LT-GaAs

Voltage

Dipole antennaE(t)Photo-conducting
antenna

EO crystal

χ(2)

χ(2)
Opticalrectification

λ/4PE(t) Electro Optic sampling
Kyoto University 2006

8THz-wave generation with second-ordernon-linear optical process
E (t )
χ(2)Pulse width: ΔτΔτ ⋅ Δω = 1

SumDifferential
frequency frequency

P (t ) = ε 0 χ E1 (t ) E2 (t )
( 2)

( 2)

E1 (t ) = E2 (t ) = A(eiωt + e −iωt )P ( 2 ) (t ) = A2 ( χ ( 2 ) (2ω , ω , ω )e i 2ωt + χ ( 2 ) (0, ω ,−ω ))SHG

Optical rectification

P ( 2ω )( 2)

Δτ ⋅ Δω = 1( 2)P ( 0)

Ω < Δω

P ( 2 ) (t ) = A2 χ ( 2) (Ω, ω + Ω,−ω ))eiΩtI(t)10.5ΔτETHz(t)-3-2-1

12

3-0.5-1-1.5-2

Kyoto University 20059Phase matching condition
ZnSeZnS

ZnTe

GaP
0.4

0.5

0.6

1.56 μm

CdTe

0.7 0.8 0.9 1.0
Wavelength (μm)

InP GaAs
1.2

1.4

1.6

k(ω+Ω) - k(ω) - k(Ω) = 0
Including dispersion:refractive index optical Index ofin THz region = group velocity
THzvisible
V phase= Vgroup

Coherent length:lc =Coherent Length (mm)Phase match condition:
108ZnTe
ω=800 nm64
200123Frequency (THz)

4c2 f nTHz − ngNahata et al., APL 69, 2321 (1996).

10

THz-wave detection
Photocurrent

EO crystal

ALT-GaAs

χ(2)

E(t)

λ/4E(t) Electro Optic sampling

Photo-conducting
antenna1PΔτ

0.5-3-2-1

1

2

3-0.5
-1
-1.5

current-2-2.5Time (ps)∞J (Δτ ) = eμ ∫ dtE THz (t ) N (t − Δτ )−∞-3

Kyoto University 200511

Non-linear THz spectroscopy
EO crystal

χ(2)State of the art in our laboratory
λ/4P(Kumiko YAMASHITA, 2005) :E(t) Electro Optic sampling– Estimation was made by EO sampling technique.

ΔIl 3= −Γ = −2π n r41 ETHz = 0.2λI

Optical pump: λ=800nm 485 mW (485 μJ /pulse)
ZnTe(ℓ=1mm、n=3.2、r41=4×10-12m/V)
PTHz= 100 pJ/pulse, 10 nJ/cm2, 10 kW/ cm2, |ETHz|～1kV/cm=100kV/m
Typically, for the non-linear spectroscopy in visible region,
we need a MW/cm2 class laser.
121021010110010-186422π20π1Fouriertransformation-2-50
5Time (ps)

100.0

1.0
2.0
Frequency(THz)

03.0

Phase (rad)3Power (log scale)Electric FIeld(arb. units)

Time-domain spectroscopy (TDS)
is a powerful tool in THz region1~−iφ (ω )i ωtE (ω ) = E (ω )e
=E(t)
edt
∫
2π
9Pulse measurements ⇒ High sensitivity. cf. FTIR
9Electric field measurements ⇒ Complex dielectric constants.

E(ω), φ(ω)

Kyoto University 2006

13

Terahertz Time-Domain Spectroscopy (THz-TDS)~Eref (ω )tvst sv~
Esam (ω )sampled~(ω )E~t (ω ) = ~samEref (ω )⎡ ( n~ (ω ) − 1)ωd ) ⎤= tvs ⋅ t sv exp ⎢i⎥⎦c⎣⎡ ( n − 1)ωd ) ⎤⎡ κωd ) ⎤= tvs ⋅ t sv exp ⎢i−exp⎥⎢
cc ⎥⎦⎣⎦⎣

Complex refractive index
n~ = n + iκ

tvs, tsv: Fresnel coefficients
2tvs = ~n (ω ) + 1
2n~ (ω )t sv = ~n (ω ) + 1(vacuum → sample)( sample → vacuum)
Kyoto University 2006

14

Compact THz-ATR spectrometer

detector
Ellipsoid mirror

ATR prismemitteremitter

Ellipsoid mirror

detector
30mm

Double-ellipsoid mirrors witha semispherical ATR prism.

ATT OC
Advanced Terahertz Technologies
adapted for Optical Communication

15

講演内容
• テラヘルツテクノロジーとは何か？
• 時間領域テラヘルツ分光法の基礎• 時間領域テラヘルツ分光法による物性測定
有機材料, 強誘電体、半導体、超伝導体
水、水溶液• 非線型テラヘルツ分光の必要性と戦略

Kyoto University 200616

Importance of terahertz frequency region
Radio wave

THz region Light wave

Dielectric constants

Intermolecular vibration
Large molecule vibration

MolecularVibration

Electronic Transition

Rotation

ε1 Relaxation mode
X-rayXdiffraction

線回折Spin excitation

ε201m100mm10mmPlasmaoscillation

Radio wave

1mm

100μm

10μm

1μm

Wavelength

100nm

10nm

1nm

0.1nm

VisibleInfrared
Kyoto University 200617

Mode-softening in KTaO3 crystal
Ichikawa, Tanaka et al.: Physical Review B 71(2005) 086509.

Reference (x1/10)

Electric Field [arb.u.]

KTaO3
300K
100K

30
20
Time [ps]ε zDelay of the pulse（Phase shift）

TO1mode49KzDecrease of the intensity

30K

zIncrease of the period

12K (x10)10Mode-softening40

THz region
ETHzω

Band-limiting

ωKyoto University 200618

Dielectric function in KTaO3Ichikawa et al.: Physical Review B 71(2005) 086509.

A single Lorentz Modelε~ (ω ) = ε∞ +(ε 0 − ε ∞ ) Ω 02Ω 0 2 − ω 2 − i γ 0ω

Fitting parametersΩ0 : Mode frequency
γ0 : Damping
ε0 :Static dielectric constant
Kyoto University 2005

19

Static dielectric constantIchikawa et al.: Physical Review B 71(2005) 086509.

Kyoto University 200520

アミノ酸結晶の吸収30x10-3Tyrosine
50K
300K

201000.00.5

1.01.52.0Frequency [THz]80x10-360Arginine
50K300K

402000.0谷他、「アミノ酸分子結晶のテラヘルツ時間領域分光」より引用
http://www.technova.co.jp/teratech/saizensen/tera_saizensen1.html

0.5

1.0

Frequency [THz]
Kyoto University 2006

21isolated bases → DNA: first step
20
cytosine (C)

40

60

-180

100120cm

2.5

3.0

3.5

3.0CdCdCMP

2.5

deoxycytidine (dC)deoxycytidinemonophosphate (dCMP)

normalized α

2.0

1.5

1.0

0.5

0.0
0.5

1.0

1.5

2.0

frequency [THz]
B. M. Fischer, M. Walther, and P. Uhd Jepsen, Phys. Med. Biol. 47 3807 (2002)

Courtesy of Peter Uhd Jepsen

22Evanescent wave in ATR
Internal total reflection conditionEvanescent wave
for p-polarization⎛ n2 ⎞
θ in > θ c = Sin ⎜⎜ ⎟⎟⎝ n1 ⎠prismEin−1EEoutθinn1β⎛ Hx ⎞ ⎛0 ⎞⎜ ⎟ ⎜ ⎟⎛ n1 k sin θ in
⎞
⎜
⎟⎟
()
HBzixt=−−βωexpexp⎜ y⎟ ⎜ ⎟⎜n2⎜ ⎟ ⎜0 ⎟⎝
⎠H⎝
⎠
⎝ z⎠
TM mode⎛ Ex ⎞ ⎛ A ⎞⎜ ⎟ ⎜ ⎟
⎛ n1 k sin θ in⎞x − ωt ⎟⎟⎜ E ⎟ = 0 exp(− βz ) exp i⎜⎜eva ⎜ y ⎟ ⎜ ⎟n2⎝⎠⎜C ⎟E⎝ z⎠ ⎝ ⎠exponentially decaying
away from the interface waves−1Eeva

k // n2xz

TM mode with
Comparable
withlargethek//
interaction length of water.
Enableto μexcite
β −1 ≈ 50msurface
modes. for water.
Best sensitivity

Kyoto University 200623

Surface plasmon in semiconductor
with THz-ATR
H. Hirori, M. Nagai, and K. Tanaka, Optics Express, 13, (26), 10801-10814 (2005).

Kyoto University 200624

Dielectric constant in doped semiconductorInAsn-typen~1017

Attenuated Total Reflection

ω << γε bω p2 1σε (ω ) = i=iγ ωω
H. Hirori, M. Nagai, and K. Tanaka, Optics Express, 13, (26), 10801-10814 (2005).
Kyoto University 2006

25

Pump and probe spectroscopy“How many-particle interactions develop after ultrafast
excitation of electron-hole plasma ”
R. Huber, F. Tauser, A. Brodschelm, M. Bichler, G. Abstrelter and A. Leitenstorfer
Nature. Vol.414 (2001) 286

Kyoto University 200426

Superconducting gap“Far-infrared optical conductivity gap in superconducting MgB2 films”
R. A. Kaindl, M. A. Carnahan, J. Orestein, D. S. Chemla, H.
M. Christen, H. Y. Zhai, M. Paranthaman and D. H. Lowndes

100nm MgB2薄膜における透過波形
6K（実線）と40K（破線）
Insetは100nm MgB2薄膜（□）と200nm
MgB2薄膜（●）の抵抗の温度変化

Phys. Rev. Lett. 88 (2002) 027003

40Kの値で規格化した透過率(b)膜厚100nm MgB26K（●）, 20K（○） 27K（◆）, 30K（◇）, 33K（■）(c)膜厚200nm MgB2（6K, 20K 25K, 30K, 36K)
6K（●）, 20K（○） 25K（◆）, 30K（◇）, 36K（■）

Kyoto University 2004

27

TD-ATR spectroscopy in water
8WaterTemperature-controlled
Si ATR prism

Re[ε]6420344K
293K

Im[ε]

6262K
265K
(Ice)

4200.0

Nagai, et al. , Int. J. IRMMW, 27, 505 (2006).

0.5

1.0
1.5
2.0
Frequency (THz)

2.5

Kyoto University 2006

3.028

Relative dielectric const.
Relativeconst.

Dielectric Constants in Water
42ε2ε1104422144220.1
0.1

KaatzeAlisonHastedThis work
Hasted ε ∞ +Water 20
20 °C°C

ε S − ε11 + iωτ D
Orientationalrelaxation
8 ps ,20 GHz
1010 10101110 111212101010
Frequency[Hz]
Frequency [Hz]A

ω02 − ω 2 + iωγIntermolecular
stretching mode
1310 13 200 fs, 5.4 THz
1029

講演内容
• テラヘルツテクノロジーとは何か？
• 時間領域テラヘルツ分光法の基礎• 時間領域テラヘルツ分光法による物性測定
有機材料, 強誘電体、半導体、超伝導体
水、水溶液• 非線型テラヘルツ分光の必要性と戦略

Kyoto University 200630

Non-linear THz spectroscopy
State of the art of the THz pulse power using fs laser
Pump power
Ti: Al2O3 laser

THz power/pulseaverage/pulse

Electric field(V/cm)

Amplifier@1KHz

650 mW

650 μJ

0.1μW

125 pJ

1 KV/cm

Oscillator with magnetic
field (Sarukura 1.7T,@80MHz)

1500 mW
650 mW

18.75 nJ
8.125 nJ

650 μW
110 μW

8.125pJ
1.375pJ

0.25 KV/cm
0.1 KV/cm

Cherenkov radiation withLiNbO3 2005

300 mW

300μ J

0.1 mW

100 nJ

30 KV/cm

MIT group (2007): １μJ （1015 photons/pulse@1KHz）
31

Non-linear THz spectroscopy• Cherenkov radiation

Cherenkov angle
32

Non-linear THz spectroscopy• Basic idea of velocity matching by pulse front using
Cherenkov effect with non-linear crystal
A. G. Stepanov, J. Hebling and J. Kuhl et al., Appl. Phys. Lett. 83, 3000 (2003).

33

Non-linear THz spectroscopy• High power single cycle THz generation using tilted
femtosecond light sources
J. Hebling and J. Kuhl et al., Appl. Phys. B 78, 593-599 (2004).

grphvvis>> vTHznvgr << nTHz

34

Non-linear THz spectroscopy• High power single cycle THz generation using tilted
femtosecond light sources : Recent status
A. G. Stepanov and J. Heebling et al., Optics Express 13 5762 (2005).

Energy efficiency
5x10-4
Quantum Efficiency:
10%

PTHz= 100 nJ/pulse, 10 nJ/cm2, 10 MW/ cm2, |ETHz|～30kV/cm=3MV/m

35