Nonlinearity in terahertz photon physics

Masaya NAGAI

Dep. Physics, Kyoto Univ. Janan

PRESTO, JST, Japan

June 15, 2010APSE2010Osaka, 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 regionVibrational mode in amino-acid microcrystal and SrTiO3

e-h system in semiconductorsOrientational motions in water

• Summary

Material Science in THz region

Plasma motion

0.1nm1nm1m1mm1m 10nm100nm10m100m10mm100mm

visble

X 線

Intramolecularvibration

Electric transition

MIR

1

2

X-raydifraction

microwave NIR UV X-ray 線

Orientationalmotion

FIR

1

2

Intermolecular vibration

Soft mode in dielectric materialSuperconductor gap …..

rot H = Jcond +4D ct

Electronics(LCR, diode, etc)

Photonics(transition between

quantum levels)

Typical timescale of damping in solids is ps.

Intense monocycle THz pulse can be assume as

i

ine2/m

Impulsive force with lowest center frequency

as intense quasi-DC field

ps timescale of damping in materials

Intense THz pulse generation with tilted pulsefront excitation

Tilted pulsefrontExcitation pulse

THz pulse

EO crystal(Mg: LiNbO3)

Review: Hebling et al. J. Opt. Soc. Am. B 25, B6 (2008)

10J

vgr cos = vTHz

Intense THz pulse in Kyoto Univ.

Output power 0.6 J Maximum filed 249 kV/cmJewariya, MN, et al., JOSAB 26, A101 (2009).

109

1010

1011

1012

1013

1014

1015

1016

Pow

er (log scale)

76543210Frequency (THz)

300

200

100

0

-100

Ele

ctric

fiel

d (k

V/c

m)

1050Time (ps)

600 J ex.

Cascaded (2) process enhances generation efficiency

MN et al. Opt. Express, 17 11543 (2009).

IMRA AMERICA FCPA Jewel D1000

Wavelength: 1045nmOutput power: 1W 10JRepetition: 100kHz Duration: 600fs

10-1

100

101

102

103

104

105

106

Pow

er (log)

3.02.01.00.0Frequency (THz)

8

4

0

-4

Ele

ctric

fiel

d (k

V/c

m)

12840Time (ps)

8.5J

3.7J

.95J

X12

X70

aExcitation pulse

Phase modulationOptical

rectification

THz pulse

EO crystal

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: amino-acid molecules

L-Arginine microcrystal has the intermolecular vibration mode at 1 THz.

60

50

40

30

20

10

0

Ab

sorp

tion

(cm

-1)

1.51.00.50.0Frequency (THz)

13K100K300K

Population

kBT

Jewariya, MN, Tanaka , submitted

Time profile of Electric pulse passed through the arginine pellet

Ele

ctri

c fie

ld (

nor

m.)

151050Time (ps)

Ref.

Arginine 300K 100kV/cm 3 kV/cm

X1/2

Jewariya, MN, Tanaka , submitted

Inte

nsi

ty

1.51.00.50.0Frequency (THz)

1.0

0.5

0.0

Op

tica

l De

nsi

ty

100 25 3 kV/cm

arginineref

sample

0.8

0.7

OD

1 10 100kV/cm

1.0THz

Ladder climbing in anharmonic potential

Above 10 stepsLadder climbing

Large E()

small E()

Jewariya, MN, Tanaka , submitted

Coherent processes in several levels system

86420Time (ps)

(a)

(b)

E (n

orm

.)P (no

rm.)

0.1 6

1.5

1.0

0.5

0.0

Im[P

/E ] (arb. units)

1.51.00.50.0Frequency (THz)

(c)

0.1 3 6

E0/h=1

iiiiiiiiiiiiii

iiii

iiiiiiiiiiiiiiiiiiiiii

tEi

tEi

dt

td

dt

td

tEi

tEi

dt

td

,1,1*

1,1,2,1,11,

*,11,

*1,

*1,,11,

*,1

*,1,1,11,11,1

,

2

P=Tr[]

nn

n-1 n-1

n+1 n+1

n+2 n+2 3 kV/cm25 kV/cm100 kV/cm

n-1,n

n,n+1

n+1,n+2

Two level system: Casperson, PRA 57, 609 (1998).

Hardening of softmodein 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).

1.5

1.0

0.5

0.0

OD

2.962.922.882.84

Energy (eV)

THz off

THz onhhlh

(b)MQWs

THz pump pulse

probe optical pulseat 10 K

nB=1

V reh

Exciton resonance disappears with blue shiftEex/eaB = 70 kV/cm

THz motions of WATER

Fukasawa et al. PRL 95, 197802 (2005)

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.

Dielectric tensor

Raman tensor

Response of water in 100m silica cell

EO s

igna

l

15105Time (ps)

ref(x1/ 5)

ref(x1/ 5)

E0

E0/ 32

Water (296K)(a)

4

3

2

1

0

-Log

(T)

1.51.00.50.0Frequency (THz)

2

1

0

Phase (rad) -20ps off

set

E0 E0/ 2 E0/ 4 E0/ 8 E0/ 16 E0/ 32

(b)

Single THz pulse responses of water

MN and Tanaka CLEO/QELS 2010

Temporal evolution of dielectric constant of water

(c)

100

50

0

-50Ele

ctri

c fie

ld (

kV/c

m)

2015105Time (ps)

pump

probe (2.5ps)

10

8

6

4

2

0D

iele

ctric

con

sta

nt

1.51.00.50.0

Frequency (THz)

-3.0 1.0 6.5 ps

ri

76543

i

50-5t (ps)

0.3

0.6THz

MN and Tanaka CLEO/QELS 2010

Even with sub-mW injection, temperature of orientational motion increase a few tens K.

Rotational motion is driven without thermal relaxation (or before heating other modes)8

6

4

2

0

Im[

]

43210

Frequency [THz]

i

362 K (89°C)335 K (62°C)313 K (40°C)295 K (22°C)278 K (5°C) 267 K (-6°C)

8

6

4

2

0

Im[

]

43210

Frequency [THz]

i295 K (22 ºC)

10

8

6

4

2

0

Re

[] r

Water10

8

6

4

2

0

Re

[]

r

H2O(a)

Yada, MN, Tanaka, CPL (2008).

Driving orientational motion of water

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 non-perturbed 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.