Achromatic waveplate in THz frequency region based on the structured parallel metal plates

Ashida LabNoriyuki Mukai

Contents• Introduction• waveplate based on the structured

parallel metal plates• THz Magnet-Optical spectroscopy• Summary and future’s prospects

Polarization-controlled spectroscopy in THz frequency region

Material characterization - Polarization dependent spectroscopy

circularly dichroic molecules magnetic resonance Hall effect …..

- Polarization modulation spectroscopy

Applications - beam isolator - encoding for displacement sensor - THz communication

Masson and Gallot OL (2006)

Weis et al APL (2009)Delacroix et al OE (2012)

Fresnel Rhomb

Jie Shan,OSA (2009)

stacked six birefringent quartz plates

Birefringence of subwavelength grating

Narrow band waveplate based on metamaterial

Waveplate in THz frequency

Adjusting CEP of single-cycle THz pulsewith parallel metal plates

TE

L=10mmTEM

g

-4

-2

0

Ph

ase(rad)

2.01.51.00.50.0Frequency (THz)

0.0

0.5

1.0

Tra

nsm

issi

vity

Po

wer

2mm

g=1mm

3mm

b

Ele

ctri

c fie

ld

50Time (ps)

ref

g=1mm

(/2 shift) 2mm

3mm

//

a

10mm

Nagai et al. Proc. otst 2013.Nagai et al. IRMMW-THz 2013 Th11-3 Phase-Sensitive THz Nonlinear Spectroscopy In High-TC Superconductor Thin Film

)2/(

112

2

gcv

c

L

c

cTE

Parallel metal waveguide with metal hole array

A. Bingham, Y. Zhao, and D. Grischkowsky,Appl. Phys. Lett. 87, 051101 (2005).

resonance frequency : ν0=c / √3p

λ/2

-4

-2

0

2

4

Ph

ase

(

rad

)

2.01.51.00.50.0Frequency (THz)

TE mode(=0º)

TM mode(=90º)

0

c

Structured parallel metal plate waveguide

TM wave propagates slowly

Positive phase perturbation due to the high-frequency resonance of the structure n0

→constant phase difference in wide frequency region

E for TE mode

E for TM mode

11

222

0

20

A

c

LTM

Our works

We fabricated the low-cost THz phase shifter using an array of structured parallel metal plates, which works the wave plate with small deviation of phase shift in wide frequency region.

We also demonstrated the generation of intense circularly-polarized THz pulse with multi and single cycle.

Fabrication of the structured parallel metal plates

9/14

We fabricated several 50×10×0.03mm3 steel plates with the periodically placed holes by the chemical etching. They were arranged using the metal spacers

Theoretically, the cut-off and the resonant frequencies should be nc=0.10 THz and n0=1.7 THz, respectively.　

qEin

p=100mm

L=10mm

g=1.5mm

a=66mm

10-2

100

102

Pow

er (

log

scal

e)

3.02.01.00.0Frequency (THz)

Experimental setup

EOdetector(CdTe)

P10 or 90 °

P2 45°

Θ

LiNbO3 emitter

E//

E⊥

Ein

Yb: fiber laserIMRA D1000(100kHz 11mJ 470fs)

50fsNonlinear optical fiber+negative dispersion fiber

1.0THzBandpass filter

Achromatic waveplate based on structured parallel metal plates

Within 5% deviation from p/2: from 0.67 to 1.21 THz

Achromatic waveplate based on structured parallel metal plates

12/14

θ=45°

θ=135°

-0.4

-0.2

0.0

0.2

0.4

E

-0.4 -0.2 0.0 0.2 0.4E//

=45º

=135º

Achromatic waveplate based on structured parallel metal plates

13/14

-2

-1

0

1

2

E

-2 -1 0 1 2E//

=45º

=135ºθ=45°

θ=135°

Achromatic waveplate based on structured parallel metal plates

14/14

Fresnel rhomeShan OE 2004

Light that is reflected from a magnetized surface can change in both polarization and reflected intensity. MO disk

Mini Disk

Magnet-Optical Kerr Effect (MOKE)

complex permittivity tensor : ε

Rright ≠Rleft

θright ≠ θleft

+ ⇔

+ ⇔

+ ⇔Kerr rotation

φ

Kerr ellipticityη

Incident

lens

lens

polarizer

λ/4 waveplate

sample

parabolic mirror

Input/outputmodule1

Input/outputmodule2

THz Magnet-Optical spectroscopy

THz Magnet-Optical spectroscopySample: InSb

THz Magnet-Optical spectroscopyInSb

THz Magnet-Optical spectroscopyInSb

We demonstrate the broadband achromatic quarter wave plate based on the structured parallel metal plates. In our artificial medium available frequency region is 0.67THz to 1.21 THz(5% phase deviation).

The center frequency and bandwidth of the wave plate based on the artificial medium can be controlled by the optimization of g, the thickness of the metal plate, and structure on the metal plates, so we can easily expand the available frequency region to the mid-infrared region.

The wave plate based on the structured metal plates will open a new polarization-sensitive spectroscopy in infrared frequency region.

Summary and future’s prospects

25μm

Sandblasting

RSm(粗さ曲線要素の平均長さ ): 30μmRa(算術平均粗さ ): 1.4μm