metamaterials for terahertz frequencies - portland state

NEAR-Lab - 1090514, gpk

NEAR-Lab Northwest Electromagnetics &

Acoustics Research

Metamaterials

for Terahertz Frequencies

Gabe Kniffin

ECE 594

Dr. Andres La Rosa

NEAR-Lab - 2040123, lmz


Acoustics Research

Outline

•

Introduction to Terahertz

•

Introduction to Metamaterials

•

Overview of Metamaterial

Switching/Modulation of THz

•

Summary



Acoustics Research

Terahertz Gap

(1)

Mickan, et.al. International Journal of High Speed Electronics and Systems, 13(2):601-676,2003(2)

Compendex

search engine http://www.engineeringvillage2.org

Journal or Conference Articles with “THz”

or “Terahertz”

in Subject/Title/Abstract (English only)

photonicsTHz gap (1)electronicsmicrowave visible x-ray

100

DC103

kilo106

mega109

giga1012

tera1015

peta1018

exa1021

zetta1024

yottaFrequency

(2)

http://www.engineeringvillage2.org/



Acoustics Research

Security

Potential Terahertz Applications

Medical Monitoring/NDE

Skin cancer3

Dental4

Drug detection5

(1)http://www.qinetiq.com/home/newsroom/news_releases_homepage/2004/3rd_quarter/QinetiQ_MORI_survey_results.html(2)http://www.technologyreview.com/Biztech/17840/(3) WOODWARD ETAL , THE JOURNAL OF INVESTIGATIVE DERMATOLOGY, VOL. 120, NO. 1 JANUARY 2003(4) www.physics.gatech.edu/gcuo/lectures/UFO22THzgeneration.ppt(5) Kawase, et al. Non-destructive terahertz imaging of illicit drugsusing spectral fingerprints, Optics Express, 2549, 6 October 2003 / Vol. 11, No. 20

Integrated circuits4

(1)

(2)

http://www.physics.gatech.edu/gcuo/lectures/UFO22THzgeneration.ppt



Acoustics Research

Why Metamaterials

for Terahertz?

•

Few natural materials with THz response

•

Potential for THz devices due to tunable material parameters



Acoustics Research

Outline

•


•


•



•

Summary



Acoustics Research


•

Veselago, 1968−

Introduced theory of materials with μ

< 0 and ε

< 0−

Predicted negative refractive index

−

“Right Handed”

vs. “Left Handed”

material

2n

HkE

EkH

c

c

HkE

EkH

c

c

V. G. Veselago. The electrodynamics of substances with simultaneously negative

values of ε

and μ. Soviet Physics USPEKHI, 10(4):509–514, January-February 1968.



Acoustics Research


•

Poynting

flux reversed from phase velocity−

Radiation tension

−

Reverse doppler

effect−

Reverse Cerenkov radiation

•

Negative refraction → “superlens”

V. G. Veselago. The electrodynamics of substances with simultaneously negative

values of ε

and μ. Soviet Physics USPEKHI, 10(4):509–514, January-February 1968.



Acoustics Research

Design of Materials with ε

< 0

J.B. Pendry, A.J. Holden, W.J. Stewart, and I. Youngs. Extremely low frequency plasmons

in metallic mesostructures. Physical Review Letters, 76(25):4773 –

4773, 1996.

•

Pendry

et al., 1996−

Plasma frequency, ωp

, for most metals is in UV range

−

ε

< 0

for ω

< ωp

−

3-D lattice of thin metal wires lowers ωp

via self-inductance



Acoustics Research

Design of Materials with μ

< 0

J.B. Pendry, A.J. Holden, D.J. Robbins, and W.J. Stewart. Magnetism from conductors and enhanced nonlinear phenomena. IEEE Transactions on Microwave Theory and Techniques,

47(11):2075 –

2084, 1999.

•

Pendry

et al., 1999−

Proposed split-ring resonator (SRR) design

−

LC resonant behavior−

Waves couple if E vector is normal to split gap or if H vector is normal to SRR plane

−

(Real)

μ

< 0

occurs at resonance



Acoustics Research

Outline

•


•


•



•

Summary



Acoustics Research

Modulation/Ultrafast

Switching via Metamaterials

Hou-Tong Chen, Willie J. Padilla, Richard D. Averitt, Arthur C. Gossard, Clark Highstrete, Mark Lee, John F. OHara, and Antoinette J. Taylor. Electromagnetic metamaterials

for terahertz applications. Terahertz Science and Technology, 1(1):42–50, March 2008.

•

Chen et al., 2008−

Used variations on Pendry’s

SRR(a) SRR(b) “Electronic Split Ring Resonator”

(eSRR)

−

Dampened resonant response via substrate conductivity manipulation:

Ultrafast

THz switching

All electronic THz modulation



Acoustics Research

Ultrafast

Switching



•

Linearly polarized THz probe pulses couple into SRRs

•

Femptosecond

pump beam excites carriers, shorting split gap, dampening resonance

•

2 Substrates:•

SI-GaAs

-

Long carrier lifetime•

ErAs/GaAs

nanoisland

superlattices

-

Short carrier lifetime



Acoustics Research

Ultrafast

Switching of THz



•

SI-GaAs

substrate•

Carrier lifetime >> THz pulse duration

•

Quasi-steady state response−

~0.5 THz absorption due to metamaterial

response

−

~1.6 THz absorption due to λ/2 resonance of unsplit

SRR sides−

Metamaterial

resonance ‘switched off’

by pump beam

•

ε

< 0 near both resonant frequencies



Acoustics Research

Ultrafast

Switching of THz



•

ErAs/GaAs

nanoisland

superlattices•

Carrier lifetime ~10 ps

within order of THz pulse duration

•

Switching recovery time measured by varying delay time between photoexcitation

and THz pulse arrival

•

Resonant behavior returns after ~ 30 ps

delay



Acoustics Research

THz Modulation via Metamaterials



•

All electronic THz modulation•

eSRRs

embedded in n-type GaAs

substrate in Schottky

diode configuration•

Conductive substrate shorts split gap, dampening resonance

•

Voltage bias creates depletion region in split gap, resulting in resonance

•

ε

< 0 near 0.75 THz and > 1.75 THz



Acoustics Research

Summary

•

THz a promising technology for spectroscopy, NDE, medical, and dental imaging

•

Metamaterials

allow the tailoring of material parameters to desired specifications

•

Metamaterials

potentially useful for THz devices

metamaterials for terahertz frequencies - portland state

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