ELECTROMAGNETICS 16 March 2011

Dr. Arje Nachman

Program Manager

AFOSR/RSE

Air Force Office of Scientific Research

AFOSR

Distribution A: Approved for public release; distribution is unlimited. 88ABW-2011-0751

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2011 AFOSR SPRING REVIEW2301K PORTFOLIO OVERVIEW

NAME: Dr. Arje Nachman

BRIEF DESCRIPTION OF PORTFOLIO:

Interrogation (Modeling/Simulation) of Linear/Nonlinear Maxwell’s Eqs

LIST SUB-AREAS IN PORTFOLIO:

Theoretical Nonlinear Optics

Wave Propagation Through Complex Media

Fundamentals of Antenna Design/Operation

Fundamentals of Effects of EM Exposure on Circuitry

Inverse Problems

Computational EM

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Subareas Funding Trends

• Wave Propagation Through Complex* Media

* Dispersive, Conductive, Random1/Turbulent, Man-Made Composites

• Antenna Design/Operation

• Inverse Problems

• Computational EM1

• Effects of EM Exposure on Circuitry

• Nonlinear Optics

(MURI on “Propagation of Ultrashort Laser Pulses through Transparent Media” began 1 Oct 2010)

1A recent NSSEFF Mathematics awardee will be looking at exactly this topic

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Scientific Challenges

• Wave Propagation Through Complex Media

Details of time-domain dynamics of EM pulses through Dispersive, Conductive, and/or

Random/Turbulent media

Research provides optimism that the class of waveforms termed Precursors have the

potential to upgrade imaging quality.

• Antenna Design/Operation Suitable PARTNERSHIPS of MATERIALS and GEOMETRY can deliver man-made

composites which exhibit novel EM attributes.

Such METAMATERIALS include: NIMs, PBGs, and “Unidirectional” composites.

Growing reliance on small UAVs drives the need to miniaturize antennas and make them more

responsive.

• Nonlinear Optics

Fundamental modeling/simulation research which addresses concerns with

femtosecond filament arrangements and plasma channel characteristics.

Advances in modeling/simulation of fiber and solid state lasers to guide the

development of compact, high energy systems.

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Transformational Opportunities

• LADAR on Cloudy Days: Two-Pronged Approach

Research in Linear EM which predicted the formation and

propagation of PRECURSORS in CLOUDS

Research in Nonlinear EM which predicted the relatively

unabated propagation of LIGHTSTRINGS through CLOUDS

• ANTENNA MINIATURIZATION

Research on “Unidirectional” composites predicted the

design of miniature antennas whose performance was

superior to current designs

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• LM Aero/Ohio State Univ

exploited novel wave slow-down

feature of the degenerate band

edge metamaterials (developed

under an AFOSR MURI at OSU) to

significantly reduce antenna size.

• The designed metamaterial FOPEN

array has 0.23 λ (3”) element

separation and λ/10 (6”) distance to

ground plane--less than half the size

and thickness of typical antennas.

• This work is part of a current

RY Metamaterials contract.

Recent Transitions

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PROJECT OBJECTIVE

investigate possibility of using wide-band, infrared (IR) pulses

for imaging through media composed of sparsely distributed

discrete particles such as clouds, fog, dust, or smoke

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ACTIVE INFRARED IMAGING THROUGH CLOUDS

and OTHER (FOG, DUST) SPARSE DISCRETE MEDIA

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Drs. Elizabeth and Marek Bleszynski

Monopole, Inc

example: a trapezoidally modulated IR pulse

Impinging on a cloud

pulse parameters: cloud parameters:

- carrier wavelength: λ = 10μm (ν = 30 THz) - average droplet radius: a ~ 5μm

- number of cycles in the pulse: m = 60 - average droplet-droplet distance: R ~ 1 mm

- rise/fall time: 0.05 of the carrier period

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Brillouin precursor-type structures

associated with leading and

trailing edges of transmitted pulse

PROPAGATION OF A WIDE-BAND IR PULSE

THROUGH SPARSE, DISCRETE MEDIA

- medium as a filter attenuating high frequencies

- evolution of propagating pulse into a Brillouin precursor

puls

e am

pli

tude

pulse amplitude after propagating

z = 100m, 200m, 300m

through the cloud medium

pulse spectrum after propagating

z = 100m, 200m, 300m

through the cloud medium

– transmitted pulse spectrum has significant

amount of low-frequency components

– high-frequency part of the spectrum is

attenuated very strongly as pulse propagates

– low-frequency part of spectrum is

weakly attenuated

ν (GHz)1 THz

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generate a coherent train of N pulses (with small rise/fall times)

emitted at linearly increasing pulse-pulse intervals

PROPAGATION OF A “CHIRPED TRAIN OF PULSES”

τ1

τ2

τ3

τ1

τ2

τ3

linearly increasing time intervals τp

between pulses

after passing through clouds the pulse train becomes a train of precursor-type pulses

associated with leading and trailing edges of the transmitted trapezoidal pulses

and attenuated approximately algebraically (not exponentially)!

τ1

τ2

τ3

this “train of precursors” is an analogue

of the conventional chirped signal

chirped train characterized by: effective center frequency and effective bandwidth

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IMAGING WITH A CHIRPED TRAIN OF PULSES

- synthetic-aperture (SA) scenario & summary of imaging

● transmitter on the aircraft emits a coherent

chirped train of wide-band IR pulses with

repetition rate of a few hundred (e.g., 220) GHz

footprint size:

~ 100m

range

~ 10 km

layer of

clouds

synthetic aperture

~ 10m … 100maircraft with

IR transmitter &

millimeter-wave receiver

ground plane

● the “precursor train” is similar to a chirped

millimeter-wave signal of center frequency

equal to the train repetition rate

(e.g., ν = 220 GHz ↔ λ = 1.4 mm)

● hence: imaging methods similar to those

used in millimeter-wave SAR can be applied

train of precursor-type pulses

after passing through clouds

● while passing through clouds high frequency

components are strongly absorbed. Each pulse

dominated by its weakly absorbed low

frequency components and acquires the shape

characteristic of a Brillouin precursor

transmitted chirped train

of pulses

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R. Albanese AFRL/RHW.P. Roach AFRL/RD

Mathematical Modeling and Experimental Validation

of Ultrafast Nonlinear Light-Matter Coupling Associated

with Filamentation in Transparent Media

MURI PM---Dr Arje Nachman (AFOSR)

J.V. Moloney ACMS/OSCM. Kolesik ACMS/OSCP. Polynkin ACMS/OSCS.W. Koch OSCN. Bloembergen OSCA.C. Newell ACMS/MathK. Glasner ACMS/MathS. Venkataramani ACMS/MathM. Brio ACMS/Math

A. BeckerA. Jaron-BeckerH. KapteynM. Murnane

C. DurfeeJ. Squier

A. GaetaD. Christodoulides R. Levis

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EXPANDED RESEARCH OPPORTUNITY IN NLO

• RECENT EXPERIMENTS HAVE REPORTED THAT 2.5 TW, 100 fs LASER PULSES

PROPAGATED COHERENTLY (WITHOUT SPREADING) FOR OVER 10 km.

• Pulses propagating vertically experience altitude-dependent density

• SUCH PULSES COULD BE EXPLOITED BY THE AIR FORCE FOR AN

OBSCURANT-PENETRATING LADAR

• Pulses do propagate “nonlinearly” through clouds and thus provide a different mechanism for such ladars

Laser

Tera WattLaser Pulse

RIA Receiver

RangeGate

No BeamSpreadingon transmitted path

Received PulseOne-way equivalent attenuation

Self-channeled“Light string”

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What if values of f are given on an arbitrary mesh

and, in addition, they contain errors? – Differentiation of interpolating polynomials is suboptimal: it reduces

the accuracy order by one (well known fact).

– Alternative (new method): Interpolate onto a Chebyshev grid, and

differentiate the resulting (Low Degree) Chebyshev expansion.

–Dr Bruno’s work has demonstrated, for the first time, derivatives

evaluated with the same order of accuracy as that inherent in the

given function values.

NUMERICAL DIFFERENTIATION OF NOISY DATADr Oscar Bruno (Applied Math, Caltech)

For example: N=30,000 corresponds to Nopt =17

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Ultrafast Lasers: Towards Attosecond Physics

Ultra-short pulses violate center-frequency expansion and therefore

NLS description is inappropriate.

Dr. Kutz (Mathematics, University of Washington)

has derived the Short-Pulse Equation

Short-Pulse Equation

SPE

saturating gain

cavity lossNonlinear gain—>intensity discrimination

spectral gain (material dependent)

Kerr Nonlinearity

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Robust Mode-Locking in SPE

Stable, self-starting mode-locking – no theoretical breakdown

3-5 fs

mode-locked

pulse

First theoretical

characterization

of ultra-short,

mode-locked

pulse formation

Farnum & Kutz, Optics Letters (Sept 15, 2010)

Spontaneous Emission

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Modeling Reconfigurable Devices

Dr. Nicholas Usechak, AFRL/RY

Instead of trying to shrink an existing system onto a photonic integrated circuit we

are investigating a new approach: dynamically addressing a segmented quantum-dot

semiconductor laser.

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gainabsorber filter

Spatially Dependent Laser Models

are Time Consuming to Solve

Simplification: Use the periodic boundary conditions to turn the

nonlinear partial differential equation system into a system of nonlinear

differential-delay equations. Solution time reduced by factor of 2,000.

Related work pursued by Dr Thomas Erneaux (Belgium) and Dr Jason Gallas (Brazil)

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The Delay Equation Model

Predicts Diversity (Bifurcations)

As the gain increases the output waveform switches regimes

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ELECTROMAGNETICS

LAB TASKS

Dr. Edward Altshuler (AFRL/RY), “Novel Antenna Design” FY09 STAR Team

1. Model Electromagnetically Small Antennas: superdirective, wide-band, conformal

2. Theory/Exploitation of Metamaterials

Dr. Bradley Kramer (AFRL/RY), “Antenna Operations”

1. Phased Arrays

Dr. Saba Mudaliar (AFRL/RY), “EM Scattering Studies”

1. Predict scattering from clutter and rough surfaces

2. Pursue research in communications through plasmas surrounding hypersonic vehicles

Dr. Kris Kim (AFRL/RY), “Predict Far-Field RCS via Near-Field Data”

(Dr.) Jason Parker (AFRL/RY), “Moving Target Radar Feature Extraction”

Dr. Nicholas Usechak (AFRL/RY), “Dynamics of Reconfigurable/Agile Quantum Dot Lasers”

1. Investigate control of amplitude-phase coupling in Quantum Dot laser systems

Dr. Timothy Clarke (AFRL/RD), “Modeling of HPM Effects on Digital Electronics”

1. Derive mathematical model predicting effects (upset) on digital electronics when exposed to various

incident EM pulses

Dr. Danhong Huang (AFRL/RV), “Models for Ultrafast Carrier Scattering in Semiconductors”

1. Model IR amplifier for extremely weak signals and distant targets

Dr. William P. Roach (AFRL/RD), “Guided Waves by Laser-Induced Filamentation”

Dr. Matthew Grupen (AFRL/RY), “Electronic Band Structure for High Speed Quantum Electron Device Simulation“

1. Modeling/Simulation of quantum tunneling devices

Dr. Iyad Dajani (AFRL/RD), “Time Dynamics of Stimulated Brillouin Scattering in Fiber Amplifiers with Frequency

Modulation”

1. SBS suppression research to realize higher power in narrow linewidth fiber amps

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Other Organizations That Fund Related Work

• NLO

1. Extensive interaction with Dr Richard Hammond/ARO on

UltraShort Laser Pulse propagation through air

2. Extensive interaction with JTO/HEL

--I manage the JTO MRI “High Power Lasers Using Optically Pumped

Semiconductor Laser (OPSL) Concepts” which ends in Aug 2012

• INVERSE SCATTERING

1. Recent interaction with Dr Joseph Myers/ARO on solving problem

of detecting IEDs

--Dr Hammond served on my FY10 USLP MURI evaluation panel and I serve

on his FY11 USLP MURI panel

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Other Organizations That Fund Related Work

• EM Effects on Circuitry

1. MURI at U Md on “Exploiting Nonlinear Dynamics for Novel Sensor

Networks” is managed by Dr. Michael Shlesinger, ONR Code 30

“The theory and analysis work you and AFOSR has been doing has been very important ...

particularly when "fast turnaround" and "hardware-centric" viewpoints tend to dominate DoD R&D

funding.” Dr William Stachnik, ONR Code 313

2. Dr Dev Palmer, ARO, invests in what can be characterized as

“Create the ultimate Army radio”. Mostly experiments and some

concern with topography

• COMPLEX MEDIA

1. Time domain approaches and optimal waveforms are mine

2. Unidirectional composites are mine

3. Negative Index Media and PBGs are ubiquitous

--I served on ONR MURI panel & my related UMd efforts are

complementary