StateState--ofof--thethe--art Terahertz art Terahertz astronomy detectorsastronomy detectors

Dr. Ir. Dr. Ir. GertGert de Langede Lange

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OutlineOutline

•• IntroductionIntroduction•• SRONSRON•• Origin, interest and challenges in (space) THz radiationOrigin, interest and challenges in (space) THz radiation

•• TechnologyTechnology•• Heterodyne mixersHeterodyne mixers•• Local oscillatorsLocal oscillators•• Low noise amplifiersLow noise amplifiers•• SpectrometersSpectrometers

•• StateState--ofof--thethe--art Instrumentsart Instruments•• Herschel/HIFI space observatory (launch 2008)Herschel/HIFI space observatory (launch 2008)•• Ground based and airGround based and air--borne telescopesborne telescopes

•• Future developmentsFuture developments

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SRONSRON

•• Mission:Mission:““SRON is the national center of expertise for the development SRON is the national center of expertise for the development and exploitation of satellite instruments in astrophysics and and exploitation of satellite instruments in astrophysics and

earth system science. It acts as the Dutch national agency for earth system science. It acts as the Dutch national agency for space research and as the national point of contact for ESA space research and as the national point of contact for ESA

programmesprogrammes”. ”.

•• Utrecht 150 peopleUtrecht 150 people•• Staff, engineering division, High Energy Astrophysics Staff, engineering division, High Energy Astrophysics

(gamma(gamma--, x, x--ray), Earth Oriented Science (atmosphere, ray), Earth Oriented Science (atmosphere, gravity), Sensor researchgravity), Sensor research

•• Groningen 70 peopleGroningen 70 people•• Local staff and engineering division, Low Energy Astrophysics Local staff and engineering division, Low Energy Astrophysics

(far(far--infrared, THz (= millimeter and subinfrared, THz (= millimeter and sub--millimeter millimeter wavelength), hosting ALMA project (ground based)wavelength), hosting ALMA project (ground based)

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THz radiation from spaceTHz radiation from space

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THz fingerprintsTHz fingerprints

•• Why study the farWhy study the far--IR?IR?

•• emission and emission and absorption lines of absorption lines of molecules, atoms and molecules, atoms and ionsions

•• 1010--200 K continuum 200 K continuum emission (dust)emission (dust)

•• formation and formation and evolution of galaxiesevolution of galaxies

•• star formation and the star formation and the physics of the physics of the interstellar mediuminterstellar medium

•• cometarycometary, planetary, , planetary, and satellite and satellite atmospheresatmospheres

THz Heterodyne receivers give detailed information on the composition and dynamics of cold (10-200 K) interstellar and atmospheric molecules

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Space THz observationsSpace THz observations

Water vapour in the atmosphere blocks large parts of the THz spectrum. For THz even a clear Dutch sky is foggy.

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Other applications. THz technology is ‘hot item’Other applications. THz technology is ‘hot item’

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THz securityTHz security

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THz technologyTHz technology

•• Two types of THz detectors:Two types of THz detectors:

•• Direct detectors (video detection, incoherent)Direct detectors (video detection, incoherent)•• Limited spectral information (f/delta f= 100Limited spectral information (f/delta f= 100--1000)1000)•• Photons converted to AC signal, spectral information with Photons converted to AC signal, spectral information with

input filters, gratings, interferometersinput filters, gratings, interferometers

•• Heterodyne detectors (coherent, phase + amplitude)Heterodyne detectors (coherent, phase + amplitude)•• Very high spectral resolution (10Very high spectral resolution (1066--101077 ))•• Photons converted to ACPhotons converted to AC--signals, spectral analysis on this signals, spectral analysis on this

signalsignal

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Heterodyne receiver main componentsHeterodyne receiver main components

Frequency

LO

Pow

er

1000 GHz

Signal Frequency domain

Frequency

Pow

er 10 GHz

IF Frequency domain

Mixer

IF-amplification

back-endspectrometer

front-end

Antenna

Local Oscillatorreference signal

diplexer

LOUFPU

HRSWBS

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1 THz Antenna Development1 THz Antenna Development

QuasiQuasi--optical antenna + lensoptical antenna + lens•• planar structureplanar structure

Waveguide + corrugated horn• demonstrated performance at

telescopes (< 1 THz)• well-defined optical beam

(determined by horn)

60 μm

240 μm

Corrugated horn

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Heterodyne mixing elements for THz astronomyHeterodyne mixing elements for THz astronomy

•• Semiconductor diodes Semiconductor diodes •• SchottkySchottky diodes diodes •• operate at room temperature, operate at room temperature,

performance improves at lower performance improves at lower temperaturestemperatures

•• Atmospheric researchAtmospheric research

•• Superconducting diodes (need of Superconducting diodes (need of cryocoolingcryocooling (liquid He 4K)(liquid He 4K)•• SIS tunnel junctionsSIS tunnel junctions•• Quantum limited detectionQuantum limited detection•• Coupling and loss limits Coupling and loss limits

operation to 1.5operation to 1.5--2 THz (2 THz (ωωRC)RC)

•• Superconducting Hot Electron Superconducting Hot Electron bolometersbolometers (operate at 4 K)(operate at 4 K)•• resistive resistive bolometersbolometers•• Easier to couple radiation at THz Easier to couple radiation at THz

frequenciesfrequencies•• Lower IF frequencyLower IF frequency

Heterodyne operation requires a non-linear I-V curve. Higher non linearity gives better performance

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SchottkySchottky mixersmixers

• Room temperature operation

• mW LO power (hard to generate)

• sensitivity 5.000-10.000 K at THz

• In use for planetary research

Whisker contact (50’s)

Planar diode (90’s)

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SIS tunnel junctions: ultimate nonSIS tunnel junctions: ultimate non--linearity and sensitivitylinearity and sensitivity

0

50

100

150

200

250

0 1 2 3 4 5Voltage (mV)

Cur

rent

( μA)

I-V (no LO) I-V (w. LO)

Vgap=2Δ

hfLO or4Δ-hfLO Isub-gap

normalstate

Vbias < 2Δ(sub-gap)

Vbias > 2Δ(normal-state)

Vbias < 2Δ(photon-assisted)

2ΔVbias

D(E)

E

hFEF

•• superconducting energy gap, 2superconducting energy gap, 2ΔΔ →→ nonnon--linear Ilinear I--V if T<V if T<TTcc ((TTcc ~ ~ ΔΔ/1.78/1.78··kkBB))•• typical values for typical values for NbNb: : TTcc ~ 9.1~ 9.1--9.3 K, 9.3 K, VVgapgap ~ 2.8 mV at T = 4.2 K~ 2.8 mV at T = 4.2 K•• RF power (RF power (hFhFLOLO) ) →→ photonphoton--assisted assisted tunnellingtunnelling →→ photophoto--current stepcurrent step•• Sensitivity quantum limited TSensitivity quantum limited TNN==hf/khf/k (receiver 250 K at 1 THz)(receiver 250 K at 1 THz)•• LO power of order 1 LO power of order 1 μμWW

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Microstrip design at THz frequencies

•• Device has capacitance, need resonant LC circuit + impedance traDevice has capacitance, need resonant LC circuit + impedance transformer to couple to the nsformer to couple to the antenna impedanceantenna impedance

Twin-Junction Tuning Circuit

junction separation = 4-7 µmjunction area = 0.6-1.0 µm2

NbTiN StriplineNb SIS Junction

SiO2 + AnodizationNbTiN Stripline

Fused Silica SubstrateAl2O3 Interface Layer

Layer Geometry

NbTiN/SiO2/Al tuning circuit:• top wire = 400 nm Al + 100 nm Nb• 200-nm SiO2 protection layer added

LC network

Impedance match

Waveguide antenna

SRON Devices fabricated at TU-Delft

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Hot electron Hot electron bolometersbolometers

•• No capacitance, easier to coupleNo capacitance, easier to couple•• Thermal device, limited Thermal device, limited

intermediate (IF) bandwidth intermediate (IF) bandwidth (phonon escape times)(phonon escape times)

•• Low LO absorption (0.1 Low LO absorption (0.1 uWuW))•• Sensitivity 700 K at THzSensitivity 700 K at THz

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Sensitivities of astronomy receiversSensitivities of astronomy receivers

Noise factor, Noise figure, Noise temperatureNoise factor, Noise figure, Noise temperature•• Noise factorNoise factor is a measure of how the is a measure of how the thethe

signal to noise ratio is degraded by a device:signal to noise ratio is degraded by a device:F=noise factor=(Sin/F=noise factor=(Sin/Nin)/(Sout/NoutNin)/(Sout/Nout))

• Noise figure is the noise factor, expressed in decibels:

NF (decibels)=noise figure =10*log(F)

• Noise temperature is another way of expressing noise, and is often used in radio astronomy.

T=noise temperature=290*(F-1)

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Noise figure, noise temperatureNoise figure, noise temperature

NF(dB) TN (°K) NF(dB) TN (°K)

0.1 7 2.1 180

0.2 14 2.2 191

0.3 21 2.3 202

0.4 28 2.4 214

0.5 35 2.5 226

0.6 43 2.6 238

0.7 51 2.7 250

0.8 59 2.8 263

0.9 67 2.9 275

1.0 75 3.0 289

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SIS and HEB sensitivity in the HIFI instrumentSIS and HEB sensitivity in the HIFI instrument

480 640 800 960 1120 1280 1440 1600 1760

100

1000

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HIFI mixer performance BaselineD

SB N

oise

Tem

pera

ture

(K)

Frequency (GHz)

1 4 5SIS

6L 6HHEB

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THz LO sources: Multiplier chains (Jet Propulsion THz LO sources: Multiplier chains (Jet Propulsion Laboratory)Laboratory)

Enormous progress in the last decade on planar device fabrication, modelling and micro-machining (μW power at THz)

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THz LO sources: Quantum Cascade Lasers (2001)THz LO sources: Quantum Cascade Lasers (2001)

mW output at THz frequencies.

Narrow frequency range

Needs cooling

2mm

Top contact

Bottomcontact

Undoped Substrate

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StateState--ofof--thethe--art THz generationart THz generation

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Low noise Cryogenic IF AmplifiersLow noise Cryogenic IF Amplifiers

•• Cryogenic Receivers:Cryogenic Receivers:•• Space communicationsSpace communications•• RadioastronomyRadioastronomy

•• 60s:60s: Maser, Parametric Maser, Parametric (18 K @ 8.45 GHz in 1964, JPL)(18 K @ 8.45 GHz in 1964, JPL)

•• 70s:70s: GaAsGaAs FET amplifiers FET amplifiers (13 K @ 1.3 GHz in 1979, NRAO)(13 K @ 1.3 GHz in 1979, NRAO)

•• 80s:80s: GaAsGaAs HEMTsHEMTs ( 5.5 K ! @ 8.5 GHz in 1988, GE( 5.5 K ! @ 8.5 GHz in 1988, GE--NRAO)NRAO)

•• 90s:90s: InPInP HEMTsHEMTs (4.6 K @ 8.5 GHz in 1999, ETH(4.6 K @ 8.5 GHz in 1999, ETH--CAY)CAY)(3.0 K @ 8.5 GHz in 2002, TRW(3.0 K @ 8.5 GHz in 2002, TRW--CAY)CAY)(2.0 K ! @ 4(2.0 K ! @ 4--8 GHz in 2002, TRW8 GHz in 2002, TRW-- CAY)CAY)

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Low noise amplifiers 4Low noise amplifiers 4--8 GHz, 48 GHz, 4--12 GHz, 12 GHz, YebesYebes

•• Amplifiers for Herschel space telescope Amplifiers for Herschel space telescope •• 2 stages of 2 stages of InPInP NGST transistors (low noise, low dissipation NGST transistors (low noise, low dissipation

2mW/stage)2mW/stage)•• Design constrained by space qualificationDesign constrained by space qualification

•• PrePre--production phase of ALMA (cryogenic production phase of ALMA (cryogenic LNAsLNAs for the European for the European contribution)contribution)

•• 3 stages of 3 stages of InPInP NGST and ETH transistors.NGST and ETH transistors.•• Based on HIFI design, with more degrees of freedomBased on HIFI design, with more degrees of freedom

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InPInP Transistor technology US, EuropeTransistor technology US, Europe

0 100 200 3000

10

20

30

40

50

60

Room vs Noise Temperature (YCF 004)

Tn (K

)

Tamb (K)

TRW TTRW T--42 CRYO342 CRYO3200200××0.1 0.1 μμm gatem gate

TRW TTRW T--45 CRYO445 CRYO4200200××0.1 0.1 μμm gatem gateUsedUsed in in DMsDMsSpaceSpace

qualifiablequalifiable,,toto be be usedused in in

FMsFMs

ETH TETH T--3535200200××0.2 0.2 μμm gatem gateExperimentalExperimentaltransistortransistor

0.22 mm0.

2 m

m

3 4 5 6 7 8 90

5

10

15

20

25

30

ETH T-35 TRW T-45 TRW T-42

YCF 2 InP devices comparisonOptimum noise bias

MGFC 4419 (GaAs)

Gai

n (d

B)

Freq. (GHz)

0.0

2.5

5.0

7.5

10.0

12.5

15.0

MGFC 4419 (GaAs)

Tn (K

)

ETH T-35 TRW T-45 TRW T-42

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MMIC developments: amplifier front ends at 100 GHzMMIC developments: amplifier front ends at 100 GHz

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Spectrometers Spectrometers

•• Analyse down converted spectrum from heterodyne Analyse down converted spectrum from heterodyne receiver. Low power, low volume, low costreceiver. Low power, low volume, low cost•• Filter banksFilter banks•• AcoustoAcousto--optical spectrometersoptical spectrometers•• Digital and Digital and analoganalog autoauto--correlatorscorrelators•• FFT spectrometersFFT spectrometers

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AcoustoAcousto optical spectrometersoptical spectrometers

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Digital autoDigital auto--correlatorcorrelator

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FFT SpectrometersFFT Spectrometers

Recent development with the advance of fast AD converters (2GHz) and FPGA logic

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FFT FFT vsvs AOSAOS

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Receiver applications of THz technologyReceiver applications of THz technology

Frequency

LO

Pow

er

1000 GHz

Signal Frequency domain

Frequency

Pow

er 10 GHz

IF Frequency domain

Mixer

IF-amplification

back-endspectrometer

front-end

Antenna

Local Oscillatorreference signal

diplexer

LOUFPU

HRSWBS

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Herschel/ HIFI

• Three instruments: PACS, SPIRE, HIFI• telescope diameter 3.5 m, temp 70-90 K• operational lifetime >3 years • height 9 m• launch mass 3300 kg• orbit Lissajous around L2• launch vehicle Ariane 5 (2008)

HIFI:• 480 – 1250 GHz and 1410 – 1910 GHz • 134 kHz – 1 MHz frequency resolutions • 4 - 2.4 GHz IF bandwidth • 12 – 40" beam • dual polarization → sensitivity &

redundancy

HIFI:Heterodyne Instrument for the Far-IR

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HIFI FM Focal Plane Unit + mixer HIFI FM Focal Plane Unit + mixer unit unit

See : http://www.sron.nl/divisions/lea/hifi/

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ALMA: 64 dish interferometer at Atacama desertALMA: 64 dish interferometer at Atacama desert

US, Japan, Europe

5000 meter altitude Chile

http://www.sron.rug.nl/alma/

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AirAir--borne observatoryborne observatory

SOFIA:

Boeing 747 airplane with on-board 2.5 meter telescope

12 km altitude

US, Germany

http://www.sofia.usra.edu/

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Summary and outlookSummary and outlook

•• Tremendous progress in the field of detectors, local Tremendous progress in the field of detectors, local oscillators, amplifiers and spectrometersoscillators, amplifiers and spectrometers

•• With current space (HIFI) and ground based (ALMA) With current space (HIFI) and ground based (ALMA) telescopes we are in a ‘golden age’ for (sub) THz astronomy.telescopes we are in a ‘golden age’ for (sub) THz astronomy.

•• But astronomers always want more:But astronomers always want more:•• Bandwidth, pixels, sensitivity, resolutionBandwidth, pixels, sensitivity, resolution

Need for:Need for:•• Low noise high bandwidth amplifiers (IF and Front end 300 Low noise high bandwidth amplifiers (IF and Front end 300

GHz) GHz) •• Fast, low power high bandwidth spectral analyzers (arrays)Fast, low power high bandwidth spectral analyzers (arrays)•• THz tuneable LO sourcesTHz tuneable LO sources•• Broadband high RF and IF bandwidth detectorsBroadband high RF and IF bandwidth detectors