Transcript スライド 1

APSE2010
Osaka, Japan
June 15, 2010
Nonlinearity in terahertz
photon physics
Masaya NAGAI
Dep. Physics, Kyoto Univ. Janan
PRESTO, JST, Japan
Colleague
M. Jewariya, H. Hirori, K. Tanaka (Kyoto Univ.)
I. Ichikawa, H. Ohtake, T. Sugiura, Y. Uehara
(Aishin seiki)
I. Katayama, H. Aoki, J. Takeda
(Yokohama National Univ.)
H. Shimosato, M. Ashida,
R. Kinjo, I. Kawayama, M. Tonouchi
(Osaka Univ.)
Outlines
• Intense THz field governs material properties
non-collinear optical rectification with LiNbO3
• nonlinear spectroscopy in THz frequency
region
Vibrational mode in amino-acid microcrystal and SrTiO3
e-h system in semiconductors
Orientational motions in water
• Summary
Material Science in THz region
Intramolecular
vibration
X-ray
difraction
e1
e
Intermolecular
vibration
Electric transition
Orientational
motion
Plasma motion
e2
1m
100mm
10mm
microwave
1mm
100mm
FIR
10mm
MIR
1mm
NIR
UV
visble
Soft mode in dielectric material
Superconductor gap …..
100nm
10nm
1nm
X
X-ray
0.1nm
g線
ps timescale of damping t in materials
4p
D
rot H = c Jcond + t
Electronics
(LCR, diode, etc)
s0
s(w) =
1-iwt
Photonics
(transition between
quantum levels)
c(w) =
ne2/me0
wT2-w2-iw/t
Typical timescale of damping t in solids is ps.
Intense monocycle THz pulse can be assume as
as intense quasi-DC field
Impulsive force with lowest
center frequency
Intense THz pulse generation
with tilted pulsefront excitation
THz pulse
EO crystal
(Mg: LiNbO3)
Tilted pulsefront
Excitation pulse
10mJ
vgr cos q = vTHz
Review: Hebling et al. J. Opt. Soc. Am. B 25, B6 (2008)
Intense THz pulse in Kyoto Univ.
300
10
600 mJ ex.
10
16
15
10
10
100
10
0
10
10
-100
10
0
5
Time (ps)
10
0
1
2 3 4 5
Frequency (THz)
6
14
13
12
11
Power (log scale)
Electric field (kV/cm)
200
10
9
7
Output power 0.6 mJ Maximum filed 249 kV/cm
Jewariya, MN, et al., JOSAB 26, A101 (2009).
Cascaded c(2) process enhances
generation efficiency
Excitation pulse
8
a
4
EO crystal
IMRA AMERICA
FCPA mJewel D1000
Wavelength: 1045nm
Output power: 1W 10mJ
Repetition: 100kHz
Duration: 600fs
0
8.5mJ
-4
Electric field (kV/cm)
Optical
rectification
Phase
modulationTHz pulse
3.7mJ
X12
.95mJ
X70
0
4
8
Time (ps)
12 0.0
MN et al. Opt. Express, 17 11543 (2009).
Large amplitude vibration
driven with intense THz pulse
Vibrational potential has anharmonicity,
and large-amplitude vibrational motions (climbing higher
excited levels) brings in dissociation, which is decisive for
chemical reaction and phase transition.
Using intense THz pulse
resonant for vibrational
modes, we can coherently
drive large amplitude
vibrational motions
Nonlinear medium: L-Arginine
L-Arginine:
60
amino-acid molecules
-1
Absorption (cm )
50
L-Arginine microcrystal has the
intermolecular vibration mode at
1 THz.
13K
100K
300K
40
30
20
10
0
0.0
kBT
Population
0.5
1.0
Frequency (THz)
1.5
Jewariya, MN, Tanaka , submitted
Arginine 300K
100kV/cm
3 kV/cm
Intensity
Time profile of Electric pulse
passed through the arginine pellet
arginine
ref
sample
Ref.
0.5
0.8
OD
Optical Density
Electric field (norm.)
1.0
100
25
3 kV/cm
0.7
X1/2
0
5
10
Time (ps)
15
0.0
0.0
1.0THz
1
0.5
10
100
kV/cm
1.0
1.5
Frequency (THz)
Jewariya, MN, Tanaka , submitted
Ladder climbing
in anharmonic potential
Above 10 steps
Ladder climbing
Large E(w)
small E(w)
Jewariya, MN, Tanaka , submitted
Coherent processes
in several levels system
di ,i (t )
dt
= -g 1i ,i  g 1i 1,i 1 - i
di ,i 1 (t )
dt
=-
P=Tr[m]
di*1,i (t )
dt
E (t )
E (t )
mi -1,i i -1,i - mi*-1,i i*-1,i  i
mi ,i 1i -1,i - mi*,i 1 i*,i 1


(
)
(
)
E (t )
E (t ) *


= - i 2p i ,i 1  (mi 1,i 1 - mi ,i )
- g 2  i ,i 1 - i
mi ,i 1 (i 1,i 1 - i ,i )




Two level system: Casperson, PRA 57, 609 (1998).
nn
n-1,n
n-1 n-1
E (norm.)
3 kV/cm
0.1
0.02
3 kV/cm
25
0.5
6
100 kV/cm
1.5
mE0/h=1
1.0
0.1
6
(b)
P (norm.)
n,n+1
n+1 n+1
(c)
(a)
0.5
0.0
0
2
4
6
Time (ps)
8
0.0
0.5
1.0
Frequency (THz)
1.5
 Im[P/E ] (arb. units)
n+1,n+2
n+2 n+2
Hardening of softmode
in SrTiO3 thin film
kBT
Katayama MN et al. CLEO/QELS 2010
THz pump-vis probe
spectroscopy in ZnSe MQW system
Hirori, MN, Tanaka,
PRB 81, 081305(R) (2010).
probe optical pulse
at
10 K
(b)
MQWs
1.5
OD
THz off
V
THz pump pulse
1.0
hh
reh
THz on
lh
0.5
nB=1
0.0
Exciton resonance
disappears with blue shift
Eex/eaB = 70 kV/cm
2.84
2.88
2.92
Energy (eV)
2.96
THz motions of WATER
Dielectric
tensor
Raman tensor
Huge orientational relaxation mode,
related to hydrogen bonding network,
lies in THz frequency region.
Raman tensor at low frequency is
little, so it is difficult to drive water
molecules via Raman induced Kerr
effect.
Fukasawa et al.
PRL 95, 197802 (2005)
Single THz pulse responses of water
(a)
(b)
Water (296K)
ref
(x1/5)
E0/32
4
-Log(T)
ref
(x1/5)
E0
2
2
1
1
0
5
10
Time (ps)
15
0.0
0
Phase (rad) -20ps offset
EO signal
3
E0
E0/2
E0/4
E0/8
E0/16
E0/32
0.5
1.0
1.5
Frequency (THz)
Response of water in 100mm silica cell
MN and Tanaka CLEO/QELS 2010
Temporal evolution of
dielectric constant of water
10
ei
(c)
100
Dielectric constant
Electric field (kV/cm)
8
pump
50
0
5
10
15
Time (ps)
4
2
probe
(2.5ps)
-50
6
20
0
0.0
7
0.3
6
5
0.6THz
4
3
-5 0 5
t (ps)
er
ei
-3.0
1.0
6.5 ps
0.5
1.0
1.5
Frequency (THz)
MN and Tanaka CLEO/QELS 2010
Driving orientational motion of water
10
(a)
Re[e]
8
Even with sub-mW injection,
temperature of orientational
motion increase a few tens K.
H2O
6
er
4
2
Rotational motion is driven
without thermal relaxation (or
before heating other modes)
0
362 K (89°C)
335 K (62°C)
313 K (40°C)
295 K (22°C)
278 K (5°C)
267 K (-6°C)
Im[e]
8
ei
6
4
2
0
0
1
2
3
Frequency [THz]
Yada, MN, Tanaka, CPL (2008).
4
Hydrogen bonding network
controlled with THz pulse
We can control water properties as SOLVENT in ps timescale,
which influence chemical reactions of solute molecules.
MN and Tanaka CLEO/QELS 2010
Summary
• We succeed intense THz pulse generation with >200 kV/cm
field amplitude.
• We demonstrate THz nonlinearity of vibration modes in amino
acide microcrystal and dielectric materials. Experimental
results is interpreted with ladder climbing in anharmonic
potential.
• We demonstrate huge spectrum modulation near the bandgap
of semiconductors with intense THz pulse, which shows nonperturbed nonlinear regime.
• We observe water molecules driven by intense THz pulses.
This motions is different from thermal effects. Results show
the reorientational motion of water molecules with breaking
hydrogen bonding in several picosecond timescale.