Observation of terahertz birefringence in aβ-BaB2O4 Crystal
E. Estacio1, S. Saito1, T. Nakazato1, Y. Furukawa1, T. Tatsumi1, M. Pham2, M.
Cadatal2, C. Ponseca2, H. Mizuseki3, Y. Kawazoe3, and N. Sarukura1
Institute of Laser Engineering. Osaka University 1, The Graduate University for Advanced Studies2,Institute for Materials Research, Tohoku University 3

Introduction and Motivation
1.

Kawase, Minamide, Ito, et.al., have previous demonstrated tunable, 0.7-2.4 THz
wave parametric generator using LiNBO3.

2.

Tanabe, Nishizawa, et.al., have also demonstrated a 3- 7 THz tunable THz source
using GaP.
These designs produce high-power THz radiation but have ns-wide THz emission
pulse widths.

3.

We have previously demonstrated high B-field enhanced, surface-illuminated InAs
wafer emitter, capable of producing picosecond THz transient pulses.

4.

LinNBO3 and GaP are excellent THz nonlinear optical materials but we intend toinvestigate other materials that can be utilized complementarily with the THz
emission spectrum of InAs.

5.

We initiate this work by investigating the THz birefringence properties of BBOcrystal.
K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett., 80, 195(2002)
T. Tanabe, K. Suto, J. Nishizawa, K. Saito, T. Kimura, Appl. Phys, Lett., 83, 237(2003)
N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, J. Appl. Phys. 84, 654 (1998)

Introduction and Motivation

The figure showing the complex experimental setup for the THz parametric generator (TPG) . The TPG gain
media consisted of two serial nonlinear crystals MgO:LiNbO3. An array of seven Si-prism couplers wasplacedon the y surface of the crystal for efficient coupling of the THz wave. The idler and THz-waves were generated
simultaneously in a direction that satisfied noncollinear phase-matching conditions. The pump used was aQ-switched Nd:YAG laser (1064 nm). A continuous-wave SLM-tunable diode laser (1.066–1.074) nm wasused as an injection seeder for the idler. The incident angle of seed was rotated, when necessary, by a mirror
on a y stage.
K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett., 80, 195(2002)

Introduction and Motivation

The figure showing the complex experimental setup for the THz parametric generator (TPG) . The TPG gain
media consisted of two serial nonlinear crystals MgO:LiNbO3. An array of seven Si-prism couplers wasplacedon the y surface of the crystal for efficient coupling of the THz wave. The idler and THz-waves were generated
simultaneously in a direction that satisfied noncollinear phase-matching conditions. The pump used was aQ-switched Nd:YAG laser (1064 nm). A continuous-wave SLM-tunable diode laser (1.066–1.074) nm wasused as an injection seeder for the idler. The incident angle of seed was rotated, when necessary, by a mirror
on a y stage.
K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett., 80, 195(2002)

InAs (100)THz radiation

B
Excitation laser

1000
Magnetic Field 1.7 T

100

×~1010InAs (100)GaAs (100)slope2

10.1

1

Excitation power (W)

++

1000

100

10Total radiation
Horizontal polarization
Vertical polarization
slope210.10.1

12

Magnetic field (T)InAsからのTHz電磁波はGaAsと比べ一桁ほど強い
原因+THz-radiation power (arb. units)

Top view

THz-radiation power (arb. units)

磁場中のInAsからのTHｚ電磁波放射(1/3 meGaAs ~ meInAs)

THz電磁波の強度は励起レーザーと磁場それぞれに２乗依存
JAP 84, 654 (1998)
THz電磁波の変換効率 １０−５〜１０−４

Future Plans
Combining these two THz generation designs…

electronFemtosecond laser

holeETHz

DipoleB field

480 mW at 1.3 THz~100 µW at 1 THz

Introduction and Motivation
1.

Kawase, Minamide, Ito, et.al., have previous demonstrated tunable, 0.7-2.4 THz
wave parametric generator using LiNBO3.

2.

Tanabe, Nishizawa, et.al., have also demonstrated a 3- 7 THz tunable THz sourceusing GaP.
These designs produce high-power THz radiation but have ns-wide THz emission
pulse widths.

3.

We have previously demonstrated high B-field enhanced, surface-illuminated InAs
wafer emitter, capable of producing picosecond THz transient pulses.

4.

LinNBO3 and GaP are excellent THz nonlinear optical materials but we intend toinvestigate other materials that can be utilized complementarily with the THzemission spectrum of InAs.

5.

We initiate this work by investigating the THz birefringence properties of BBO
crystal.
K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett., 80, 195(2002)
T. Tanabe, K. Suto, J. Nishizawa, K. Saito, T. Kimura, Appl. Phys, Lett., 83, 237(2003)
N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, J. Appl. Phys. 84, 654 (1998)

Experiment100 fs, 800 nm, 80 MHz

Bolometer
Lock-inamplifier
Bolometer

chopperInAs(100)

Transient pulses
centered at ~0.8THz ranging from
0.1 THz to ~1.51T
magnetic
field

Michelson
Interferometer

WG
power

spectraWG

flat
mirrorwire gridpolarizer

paraboloidal
mirrorparaboloidal
mirrorType I 10mm x 10 mm x 1 mm (thick) BBO crystal (Type I, θ=900, Φ=900, Crylight Photonics, Inc.) mounted on rotating holder

Results

Azimuthal angle dependence of the 800 nm and broadband THz
transmission of the BBO crystal, showing birefringence. The 00 orientation
coincides with the crystal’s c-axis.

Results

Terahertz transmission spectra for selected azimuthal angle orientations. Astrong absorption band at 0.65 THz for the 40o to 60o orientations is attributed
to low frequency phonon modes of the [B3O6]3- rings. The BBO crystal
exhibits 60% transmittance at 0.35 THz. We surmise, this is better than what
was experimentally observed for LiNBO3.

Results
Illustration of the calculated
phonon modes of the [B3O6]3rings at ~27 cm-1.

The projection of the calculated
dipole moments to the y-z
plane. The angular orientationofthedipole
derivative
projections with respect to thec-axis coincides with theorientation
wheretheabsorption at the 0.65 THzband was observed.

Results
THz Transmittance

1 .0T0T40
T60
T900 .80 .60 .40 .20 .00 .20 .40 .60 .8

1 .0

F re q u e n c y ( T H z )The angular dependence of the calculated refractive index values areshown in the open circle trace while the continuous line trace is a leastsquares fit.
no ~ 2.79
ne ~ 2.50

Conclusions and Future Plans
We report experimental work on the optical properties of BBO in the0.1 to 1.1 terahertz (THz) region. Primarily, results show that thismaterial is significantly more transparent for submillimeter waves than
LiNBO3 and it was demonstrated that this material also exhibits
birefringence in the THz range.
These findings could prove vital in utilizing phase matching conditions
to realize BBO-based optical parametric devices operating the THz
region.

Future Plans
Combining these two THz generation designs…

electron

Femtosecond laser

holeETHz

DipoleB field

480 mW at 1.3 THz~100 µW at 1 THz

Future Plans
Design and development of a THz Optical Parametric Amplifier
800nm 100 fs at 82
MHz optical excitation
for semiconductor
surface THz emitter

Noncollinear phase-matching condition
for difference frequency generatio (DFG)
The pump can stimulate a Stokes photon
to generate the idler beam.
kT

Idler from DFG
Broadband THz pulses
from semiconductor

Amplifiedbroadband THz
pulse

kikp
TransmittedTHz pulses

SamplecellTHz Emitter
B field

Nonlinear crystal (BBO/LBO)

532 nm 12 ps at 80 MHz pump laser

FTIR spectrometer/Bolometer半導体表面からのテラヘルツ電磁波発生と磁場による増強

InAs表面

キャリアの加速度

フェムト秒パルス

電子ETHz

磁場 B 〜5T FEFBp
テラヘルツ電磁波パルス

各種パラメーターへの依存性の調査及び最適条件の探索
高輝度光源の開発
増幅メカニズムの解明∂v ∂ 2 pea(t ) ∝ ∝ 2 ∝ − ( Esuf + v × B)∂t ∂tme
テラヘルツ電磁波強度r22ITHz = E ∝ ∂J = nea(t)∂t2THz

⎛
⎜
⎜
⎜⎜⎜
⎝

⎞⎟
⎟
⎟⎟⎟
⎠

⎛⎜
⎜⎜
⎝

•半導体•励起レーザー
有効質量 出力
表面状態 入射角度
偏光
温度
パルス幅
チャープ量

⎞⎟
⎟⎟
⎠

•磁場強度
印加方向

磁場によるテラヘルツ電磁波発生の効率向上@ Prof. X. -C. Zhang group
Rensselaer Rolytech. Inst.
@ APL. 62, 2003 (1993)+dvea== - * E +v × B
dtme

磁場に対する２乗依存性– GaAsの重い有効質量– ０.２ Tの低い磁場– １００ｍW程度の低励起磁場によるテラヘルツ電磁波発生の効率向上について、深入りをX. -C. Zhang はしなかった