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Overview of new

ultrafast research initiative

within ODM Research Group

Jeremy Allam

Optoelectronic Devices and Materials Research Group

Tel +44 (0)1483 876799Fax +44 (0)1483 876781

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University of Surrey

School of Physics and Chemistry

Guildford, SurreyGU2 7XH, UK

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optical communicationsTerabit/second optical

networks are here!

• SOA-based optical switches for all-optical network

• limited above ~100Gbit/s by intraband carrier dynamics

ultrafast

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ultrafast revolutionelectro-

optic sampling

free-space THz

coherent controlNL pulse

propagationmicrowave photonics

ultrafast opto-electronics

biological / environ-mental

sensing

photo-chemistry

medical applicationsmaterial

processingnon-

linear optics

non-stochastic breakdown

optical spectro-scopy

high-energy physics

solid-state femtosecond

lasers

intense(>1TW)

tunable(UV-MIR)coherentultrashort (<10fs)relativistic electron motion

high-harmonic

generation (UV, X-ray)

controllable ablationTHz

device physics

ultrafast

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aspects of research at Surrey(1) bandstructure engineering of material / device dynamics

• theory (beyond effective mass)• design (optimise device dynamics)• diagnostics (high-pressure experiments)

(2) advanced experimental and theoretical methods• femtosecond lasers, OPOs, OPA; FELIX• broadly-tunable, ultrashort, high-intensity light pulses• comprehensive, first-principles theoretical models

(3) femtosecond physics in advanced real-world devices

(4) convergence of optics and electronics• interband AND intraband dynamics• optical transitions AND electron transport • high-speed photonics AND microwave electronics• ultrafast optics AND mid/far-infrared spectroscopy

(5) time + frequency domain characterisation• (ω,τ) optical methods (e.g. FROG) for amplitude, phase dynamics• electro-optic sampling for THz device / circuit characterisation• optical pulse shaping for all-optical bit-error-rate measurement?

ultrafast

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research activities(1) Mid-infrared time-resolved experiments - FELIX

Dr. Ben Murdin

(2) Theory of ultrafast interactions in semiconductors Dr. Steve Hughes

(3) Ultrafast optical / electronic devices Prof. Jeremy Allam

JA

ATI occupation

fs experiments start

SH

BNM

1996 1997 1998 1999 2000 2001 20021 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10

ultrafast

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research activities 1

(i) Mid-infrared lasers

(ii) Time Resolved spectroscopy with FELIX

(iii) New infrared materials: InSbN

(1) Experimental studies of intersub-band transitions and mid-infrared devices - Dr. Ben Murdin

ultrafast

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Mid-infrared lasers Electrically pumped

semiconductor laser Small, low cost, rugged Pollution monitoring,

process control etc applications

Mechanisms preventing room temperature operation Elastic collisions between

charges (Auger effect) valence band absorption phonon emission (=heat!)

Solution = band-structure engineering quantisation strain

Conventional interband device

Quantum Cascade device

C O

ultrafast

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Spectroscopy with FELIXFree Electron Laser for Infrared eXperiments, Utrecht, NL

Tuneable from 4 -250mm!! 1MW peak power!! Pulses only 6 optical cycles!!!

Example experiments: Pure and applied physics scattering/recombination

times between charges on femtosecond scale

searching for excited states in new materials like quantum dots, polymers, buckyballs

new fundamental regimes of ultra-short times and ultra-high a.c. electric fields

ultrafast

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New infrared materials: InSbN Adding dilute N to III-V semiconductors gives strong

bandgap bowing (energy decreases) long emission from wide-gap constituent materials

electron effective mass increases, suppressing Auger

ultrafast

pump-probe using FELIX shows lifetime in an InSbN sample with 11m gap () is much longer than for HgCdTe of same gap and same excitation (—) [only slightly faster than InSb (···) and HgCdTe with 7m gap (- -)]

Normally Auger increases exponentially with reducing gap 0 200 400 600

0.37

1.00

290K

T/T

(ar

b. u

nits

)

probe delay (ps)

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research activities 2(2) Fundamental theory of ultrafast electron-photon

interactions in semiconductors - Dr. Steve Hughes

• many-body quantum theory of semiconductor optics:• Rabi flopping, excitonic trapping • inverted semiconductors• pulse reshaping in SOAs • modulation of lasers and SOAs through THz field

• Few-cycle optical pulse propagation• beyond slowly-varying envelope approximation

• Extremely-excited states• fs optical pulse, THz field, magnetic field• dynamic Franz-Keldysh effect• magneto-excitons - dancing with wavepackets

ultrafast

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theory of inverted semiconductorsultrafast

previous: • Rate Equation Model (REM)• phenomenological NL gain and saturation*• adiabatic light-matter interaction

• coherent effects (phase storage)• non-transferable NL parameters

so use a first-principles, microscopic approach:

*via: two-photon absorption (TPA), free-carrer absorption (FCA), spectral hole burning (SHB), carrier heating (CH)

but experiments on SOAs show:

• semiconductor Maxwell-Bloch equations• diagonal and non-diagonal dephasing• many-body carrier-carrier interactions

future improvements:• band-structure effects• non-Markovian dynamics

state-of-the-art description of semiconductor gain

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Extremely excited ultrafast wavepackets

• newly available sources (Terawatt lasers, ultrashort pulse lasers, free-electron lasers...) allow extreme excitations

• theoretical treatment requires non-perturbative, many-body quantum approach...... and reveals new phenomena

optical excitation

+THz field

+magnetic

field

dancing wavepackets

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research activities 3(3) Ultrafast measurements of optical and electronic

devices - Prof. Jeremy Allam

• optoelectronic devices: lasers and SOAs• fs pulse propagation in semiconductor LD - ‘solitonic dark pulses’• key questions:

• How to modulate lasers faster?• How to increase bandwidth of all-optical switch?

• ultrafast photodetectors:• ultrafast photoconductors• TW-WG PD/PT (with Prof.’s Robertson and Weiss)• dynamics of impact ionisation (with Sheffield)

• mid-infrared dynamics • dynamics dominate CW performance...• compare interband, type II and intraband (QC) devices

• ultrafast electronics• THz electro-optic measurements of devices and circuits • new concepts for THz electronics

ultrafast

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modulation of lasersultrafastcurrent

electro-absorption

optical pulse(Elsaesser ‘97)eV

mid-infrared(Gorfinkel ‘92)

MIR

optical pulse

THz pulse(Hughes ‘98)THz

pulse

intraband processes

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optical switch dynamicsultrafastModulator

MZ

actual response

desired response

SMZ

bandstructure engineering of dynamics?

NLDf1Df2NL

NLDfinputcontroloutput

Dftp

DftDf1Df2

Dft0.1 ps NL100ps recombination

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Ultrafast laser experimentsnew femtosecond laser laboratory

Ti-sapphire laser + Optical Parametric Oscillator (100fs, 0.7-1.6µm)Short-Pulse Ti-sapphire laser (<50fs, 800nm)Optical Parametric Amplifier (<50fs, 1.0-2.4µm, -10µm with DFM)

experimental methodspump-probe; upconversioncoherent spectroscopy; time-frequency methods (e.g. FROG)electro-optic / THz sampling

experimentsnew phenomena in propagating femtosecond pulses laser and optical amplifier dynamicsfemtosecond dynamics of mid-infrared materials and structuresTHz optical sampling of electron devices and materials

mid-IR

visiblenear-IR

<50fs