odmodm overview of new ultrafast research initiative within odm research group jeremy allam...
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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
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