of-the-art Terahertz astronomy detectors Dr. Ir. Gert de Lange

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1 State-of of-the-art Terahertz astronomy detectors Dr. Ir. Gert de Lange

2 Outline Introduction SRON Origin, interest and challenges in (space) THz radiation Technology Heterodyne mixers Local oscillators Low noise amplifiers Spectrometers State-of of-the-art Instruments Herschel/HIFI space observatory (launch 2008) Ground based and air-borne telescopes Future developments 2

3 SRON Mission: SRON is the national center of expertise for the development and exploitation of satellite instruments in astrophysics and earth system science. It acts as the Dutch national agency for space research and as the national point of contact for ESA programmes. Utrecht 150 people Staff, engineering division, High Energy Astrophysics (gamma-,, x-ray), x Earth Oriented Science (atmosphere, gravity), Sensor research Groningen 70 people Local staff and engineering division, Low Energy Astrophysics (far-infrared, THz (= millimeter and sub-millimeter wavelength), hosting ALMA project (ground based) 3

4 4

5 THz radiation from space 5

6 THz fingerprints Why study the far-ir? emission and absorption lines of molecules, atoms and ions K continuum emission (dust) formation and evolution of galaxies star formation and the physics of the interstellar medium cometary,, planetary, and satellite atmospheres THz Heterodyne receivers give detailed information on the composition and dynamics of cold ( K) interstellar and atmospheric molecules 6

7 Space THz observations Water vapour in the atmosphere blocks large parts of the THz spectrum. For THz even a clear Dutch sky is foggy. 7

8 Other applications. THz technology is hot item 8

9 THz security 9

10 THz technology Two types of THz detectors: Direct detectors (video detection, incoherent) Limited spectral information (f/delta f= ) 1000) Photons converted to AC signal, spectral information with input filters, gratings, interferometers Heterodyne detectors (coherent, phase + amplitude) Very high spectral resolution ( ) Photons converted to AC-signals, spectral analysis on this signal 10

11 Heterodyne receiver main components Signal Frequency domain Power LO 1000 GHz Frequency diplexer FPU Antenna Mixer Local Oscillator reference signal LOU IF-amplification Power 10 GHz Frequency IF Frequency domain front-end HRS WBS back-end spectrometer 11

12 1 THz Antenna Development Waveguide + corrugated horn demonstrated performance at telescopes (< 1 THz) well-defined optical beam (determined by horn) Quasi-optical antenna + lens planar structure 60 μm 240 μm Corrugated horn 12

13 Heterodyne mixing elements for THz astronomy Semiconductor diodes Schottky diodes operate at room temperature, performance improves at lower temperatures Atmospheric research Heterodyne operation requires a non-linear I-V curve. Higher non linearity gives better performance Superconducting diodes (need of cryocooling (liquid He 4K) SIS tunnel junctions Quantum limited detection Coupling and loss limits operation to THz (ωrc)( Superconducting Hot Electron bolometers (operate at 4 K) resistive bolometers Easier to couple radiation at THz frequencies Lower IF frequency 13

14 Schottky mixers Whisker contact (50 s) Planar diode (90 s) Room temperature operation mw LO power (hard to generate) sensitivity K at THz In use for planetary research 14

15 SIS tunnel junctions: ultimate non-linearity and sensitivity E 250 D(E) V bias E F 2Δ hf Current (μa) hf LO or V gap =2Δ normal state 50 4Δ-hf LO I sub-gap Voltage (mv) V bias < 2Δ (sub-gap) V bias > 2Δ (normal-state) V bias < 2Δ (photon-assisted) I-V (no LO) I-V (w. LO) superconducting energy gap, 2Δ2 non-linear I-V I V if T<T c (T c ~ Δ/1.78 k B ) typical values for Nb: T c ~ K, V gap ~ 2.8 mv at T = 4.2 K RF power (hf( LO ) photon-assisted tunnelling photo-current step Sensitivity quantum limited T N =hf/k (receiver 250 K at 1 THz) LO power of order 1 μw 15

16 Microstrip design at THz frequencies Layer Geometry NbTiN Stripline Nb SIS Junction SiO 2 + Anodization NbTiN Stripline Twin-Junction Tuning Circuit LC network Waveguide antenna Al 2 O 3 Interface Layer Fused Silica Substrate NbTiN/SiO 2 /Al tuning circuit: top wire = 400 nm Al nm Nb 200-nm SiO 2 protection layer added Impedance match SRON Devices fabricated at TU-Delft junction separation = 4-7 µm junction area = µm 2 Device has capacitance, need resonant LC circuit + impedance transformer to couple to the antenna impedance 16

17 Hot electron bolometers No capacitance, easier to couple Thermal device, limited intermediate (IF) bandwidth (phonon escape times) Low LO absorption (0.1 uw) Sensitivity 700 K at THz 17

18 Sensitivities of astronomy receivers Noise factor, Noise figure, Noise temperature Noise factor is a measure of how the the signal to noise ratio is degraded by a device: F=noise factor=(sin/nin)/(sout/nout Nin)/(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) 18

19 Noise figure, noise temperature NF(dB) T N ( K) NF(dB) T N ( K)

20 SIS and HEB sensitivity in the HIFI instrument DSB Noise Temperature (K) HIFI mixer performance Baseline SIS L HEB 6H Frequency (GHz) 20

21 THz LO sources: Multiplier chains (Jet Propulsion Laboratory) Enormous progress in the last decade on planar device fabrication, modelling and micro-machining (μw power at THz) 21

22 THz LO sources: Quantum Cascade Lasers (2001) mw output at THz frequencies. Narrow frequency range Bottom contact 2mm Top contact Needs cooling Undoped Substrate 22

23 State-of of-the-art THz generation 23

24 Low noise Cryogenic IF Amplifiers Cryogenic Receivers: Space communications Radioastronomy 60s: Maser, Parametric 70s: GaAs FET amplifiers 80s: GaAs HEMTs 90s: InP HEMTs ( GHz in 1964, JPL) ( GHz in 1979, NRAO) ( GHz in 1988, GE-NRAO) ( GHz in 1999, ETH-CAY) ( GHz in 2002, TRW-CAY) ( GHz in 2002, TRW- CAY) 24

25 Low noise amplifiers GHz, GHz, Yebes Amplifiers for Herschel space telescope 2 stages of InP NGST transistors (low noise, low dissipation 2mW/stage) Design constrained by space qualification Pre-production phase of ALMA (cryogenic LNAs for the European contribution) 3 stages of InP NGST and ETH transistors. Based on HIFI design, with more degrees of freedom 25

26 InP Transistor technology US, Europe 0.2 mm TRW T-42 T CRYO μm m gate ETH T-35 TRW T-45 TRW T-42 YCF 2 InP devices comparison Optimum noise bias ETH T-35 TRW T-45 TRW T mm TRW T-45 T CRYO μm m gate Used in DMs Space qualifiable, to be used in FMs Gain (db) MGFC 4419 (GaAs) Freq. (GHz) MGFC 4419 (GaAs) Tn (K) ETH T-35T μm m gate Experimental transistor Tn (K) Room vs Noise Temperature (YCF 004) Tamb (K) 26

27 MMIC developments: amplifier front ends at 100 GHz 27

28 Spectrometers Analyse down converted spectrum from heterodyne receiver. Low power, low volume, low cost Filter banks Acousto-optical optical spectrometers Digital and analog auto-correlators FFT spectrometers 28

29 Acousto optical spectrometers 29

30 Digital auto-correlator 30

31 FFT Spectrometers Recent development with the advance of fast AD converters (2GHz) and FPGA logic 31

32 FFT vs AOS 32

33 Receiver applications of THz technology Signal Frequency domain Power LO 1000 GHz Frequency diplexer FPU Antenna Mixer Local Oscillator reference signal LOU IF-amplification Power 10 GHz Frequency IF Frequency domain front-end HRS WBS back-end spectrometer 33

34 Herschel/ HIFI Three instruments: PACS, SPIRE, HIFI telescope diameter 3.5 m, temp K operational lifetime >3 years height 9 m launch mass 3300 kg orbit Lissajous around L2 launch vehicle Ariane 5 (2008) HIFI: Heterodyne Instrument for the Far-IR HIFI: GHz and GHz 134 khz 1 MHz frequency resolutions GHz IF bandwidth 12 40" beam dual polarization sensitivity & redundancy 34

35 HIFI FM Focal Plane Unit + mixer unit See : 35

36 ALMA: 64 dish interferometer at Atacama desert US, Japan, Europe 5000 meter altitude Chile 36

37 Air-borne observatory SOFIA: Boeing 747 airplane with on-board 2.5 meter telescope 12 km altitude US, Germany 37

38 Summary and outlook Tremendous progress in the field of detectors, local oscillators, amplifiers and spectrometers With current space (HIFI) and ground based (ALMA) telescopes we are in a golden age for (sub) THz astronomy. But astronomers always want more: Bandwidth, pixels, sensitivity, resolution Need for: Low noise high bandwidth amplifiers (IF and Front end 300 GHz) Fast, low power high bandwidth spectral analyzers (arrays) THz tuneable LO sources Broadband high RF and IF bandwidth detectors 38