1. Basic Detection Techniques Front-end Detectors for the Submm Andrey Baryshev Lecture on 21 Sept 2006

2. Basic Detection Techniques – Submm receivers (Part 3)2 Outline Stability measurements of practical receiver system, Allan variance plot, calibration intervals Stability measurements of practical receiver system, Allan variance plot, calibration intervals Direct detectors (principle) Direct detectors (principle) Photo-detectors Photo-detectors Bolometers Bolometers Other types (pyro-detectors, Golay cell) Other types (pyro-detectors, Golay cell) Noise in direct detectors Noise in direct detectors NEP -- noise equivalent power NEP -- noise equivalent power Photon noise Photon noise Electronics noise Electronics noise Low noise detectors in submm THz region Low noise detectors in submm THz region Transition edge sensors Transition edge sensors Kinetic inductance detectors Kinetic inductance detectors SIS junction as direct detector SIS junction as direct detector Practical measurement of NEP Practical measurement of NEP

3. Basic Detection Techniques – Submm receivers (Part 3)3 Practical receiver at a telescope/or any lab T sys, G sys T hot T cold Telescope T sky (t) CalibratorReceiverBack-end Front-end Signal amplitude = 1 K on top of 100 K background Spectrometer bin bandwidth = 1 MHz, Tsys = 100 K f a 100 K Source spectrum 1 - bin What to do to detect with accuracy 5 σ (S/N=5)?

4. Basic Detection Techniques – Submm receivers (Part 3)4 Integrate (wait)! How long? T sky Radiometer equation Uncertainty dT τ B dT = T sky 2 dT 2 B τ = NOTE: T sky = T bkg +T sys = 200 K, 201 K for the line! Not T sys ! dT = 1 K / 5 (S/N) = 0.25 K Ideally after continuous integration of 0.64 s accuracy is achieved!

5. Basic Detection Techniques – Submm receivers (Part 3)5 Why radiometer equation? Fundamental noise is photons -> statistics is “white” noise: uniform spectral density Fourier -> transform White photon noise statistics results in radiometer equation

6. Basic Detection Techniques – Submm receivers (Part 3)6 Real life receivers Ideal Real System instability: Standing waves, drift, 1/f noise, ambient temperature, Atmosphere, many more … How often do we need to calibrate (loose time)?

7. Basic Detection Techniques – Submm receivers (Part 3)7 Allan variance s 1,s 2 … s n … s N Measurement sequence with minimum integration time t min 1 2 σ(t) 2 = where y n is the average of subset of s n over integration time t s1s1 s2s2 s3s3 s4s4 s5s5 s6s6 s7s7 s8s8 s9s9 s 10 s 11 s 12 s 13 s 14 s 15 s 16 y1y1 y2y2 y3y3 y4y4 y5y5 y6y6 y7y7 y8y8 y1y1 y2y2 y3y3 y4y4 2t 4t …

8. Basic Detection Techniques – Submm receivers (Part 3)8 Allan time Maximum integration time between recalibrations ideal real

9. Basic Detection Techniques – Submm receivers (Part 3)9 Direct detector principles Direct detector gives signal proportional to the power of incoming radiation or amount of photons. Usually detector pixel is much simpler than heterodyne counterpart, so large arrays are possible Photo detector (electronic) Photo detector (electronic) Bolometric principle (Thermal detectors) Bolometric principle (Thermal detectors) Coherent detectors (diode) Coherent detectors (diode) Other principles Other principles

10. Basic Detection Techniques – Submm receivers (Part 3)10 Parameters of direct detectors Quantum efficiency Quantum efficiency Noise Noise Linearity Linearity Dynamic range Dynamic range Number and size of pixels Number and size of pixels Time response Time response Spectral response Spectral response Spectral bandwidth Spectral bandwidth

11. Basic Detection Techniques – Submm receivers (Part 3)11 NEP NEP is input power at the input of the detector to produce SNR=1 One can add the contributions of different noise sources in square fascion as in the formula ebove for optics noise contribution

12. Basic Detection Techniques – Submm receivers (Part 3)12 Photon noise and Johnson noise Detector is limited by statistics of incoming photons 2hc(kT) 1/2 ηλqGR 1/2 NEP = Detector is limited by Johnson noise (thermal fluctuations) 2hc(1/t) 1/2 λ η 1/2 NEP =

13. Basic Detection Techniques – Submm receivers (Part 3)13 Black body facts Photon occupation numbers Uncertainty in photon numbers Photon NEP Stefan-Boltzmann law M = σT 4 Φ = 4 π R 2 LL= e (2 h f 3 )/(c/n) 2 /(Exp(hf/(kT))-1)

14. Basic Detection Techniques – Submm receivers (Part 3)14 Photo detectors Arriving photon generate/modify free charge carriers distribution Classical semiconductor (utilizing band gap) Classical semiconductor (utilizing band gap) It has a lower frequency limit hF > E gap It has a lower frequency limit hF > E gap Typical semiconductor work in IR region Typical semiconductor work in IR region By applying stress to the crystal, it is possible to decrease E gap Like in stressed germanium By applying stress to the crystal, it is possible to decrease E gap Like in stressed germanium SIS junction SIS junction No low frequency limit (effective band gap modified by bias point) No low frequency limit (effective band gap modified by bias point) High frequency limit due to gap structure High frequency limit due to gap structure Kinetic inductance detectors Kinetic inductance detectors Photons break Cupper pairs Photons break Cupper pairs It has low frequency limit It has low frequency limit hF > Egap E

15. Basic Detection Techniques – Submm receivers (Part 3)15 Example Detectors PACS instrument on Herschel, Stressed germanium

16. Basic Detection Techniques – Submm receivers (Part 3)16 21 CPW Through line CPW ¼ Resonator Coupler Antenna substrate Central conductor 100  m L= 5 mm @ 6 GHz Al ground plane Readout signal ~GHz 21 KID arrays for Astronomy Principle of Kinetic Inductance Detection Pair breaking detector Superconductor ~ L KIN at T<Tc/3 Superconductor ~ L KIN at T<Tc/3 L KIN ~ N qp ~ power absorbed L KIN ~ N qp ~ power absorbed Use L KIN to measure absorbed power Use L KIN to measure absorbed powerKID a SC material in resonance circuit read out at F 0 ~ 4 GHz read out at F 0 ~ 4 GHz resonance feature is function of N qp resonance feature is function of N qp signal in S 21 or R and θ signal in S 21 or R and θ

17. Basic Detection Techniques – Submm receivers (Part 3)17 KID arrays KID radiation coupling Antenna in focus of Si lens Herschell band 5 & 6 Radiation from sky F RF >>2Δ/h -> increases N qp -> change in S 21 or R and θ F 0 << F RF antenna << resonator F 0 << 2Δ/h No qp creation due to readout Radiation Si Lens 21 CPW Through line CPW ¼ Resonator Coupler Antenna substrate Central conductor 100  m L= 5 mm @ 6 GHz Al ground plane Most sensitive area Readout signal ~GHz 21

18. Basic Detection Techniques – Submm receivers (Part 3)18 KID arrays Principle of KID arrays Resonances @ F 0 Resonances @ F 0 F 0 set by geometry (length) F 0 set by geometry (length) Intrinsic FDM Intrinsic FDM

19. Basic Detection Techniques – Submm receivers (Part 3)19 KID arrays for astronomy General idea for the FP Optical Interface Optical Interface flies eye array of Si lenses, size 20Fλ/2. 90.6% packing efficiency in hexoganal Array Array Detectors printed on back Si lens array Readout Readout 4 SMA coax connectors 2 full chains -> redundancy ~5000 pixel 0.48 mm

20. Basic Detection Techniques – Submm receivers (Part 3)20 KID focal plane for NIKA 400 pixel test array for 2 mm antenna KID Through line

21. Basic Detection Techniques – Submm receivers (Part 3)21 Pair breaking detector: fundamental sensitivity limit DOS e-p coupling # quasiparticles quasiparticle lifetime 1 sec Pmax/NEP>10.000

22. Basic Detection Techniques – Submm receivers (Part 3)22 Measuring Dark NEP ~ IQ Synthesizer Quadrature mixer Re Im ADC analyses Superconductor Shorted end Open end, coupler 12 Cryostat LNA Measure bare resonators Measure bare resonators Measure all ingredienst of NEP Measure all ingredienst of NEP Quasiparticle lifetime qp Quasiparticle lifetime qp noise S x noise S x Quasiparticle responseδx/δN qp Quasiparticle responseδx/δN qp For R and θ For R and θ Noise Signalqp roll-off θ or R

23. Basic Detection Techniques – Submm receivers (Part 3)23 photonphoton Δ Δ EE EFEFEFEF EFEFEFEF qVqV ・ High sensitive in far-IR – sub-mm region q: elementary charge h:plank constant ν:frequency I sg : subgap current η: quantum efficiency Quantum type detector with superconductor SuperconductorSuperconductor Bias voltage, V InsulatorInsulator SuperconductorSuperconductor @ 600 GHz Our goal: Current status: 10 -16 ～ 10 -17 W/√Hz SIS junction Density of states

24. Basic Detection Techniques – Submm receivers (Part 3)24 7/15/2015 24 4.2 K 1.6 K Bias voltage [ V ] Current [ A ] D(E):density of states, F(E): Fermi function, Δ: gap energy Nb/Al-AlN/Nb junction Tinkham (1975) ? Theoretical curves

25. Basic Detection Techniques – Submm receivers (Part 3)25 Transition edge sensor principle Thin superconducting film as thermometer Square law power detector thermal time constant t = C/G C: thermal capacitance G: thermal conductivity

26. Basic Detection Techniques – Submm receivers (Part 3)26 Procedure of an NEP measurement Determine the signal power Determine the signal power It is given by Planck formula It is given by Planck formula Need temperature of calibrator black-bodies Need temperature of calibrator black-bodies Frequency coverage of the detector (measured by FTS) Frequency coverage of the detector (measured by FTS) Knowledge of solid angle of antenna beam pattern Knowledge of solid angle of antenna beam pattern Determine the responsively Determine the responsively Measure response from hot/cold radiators Measure response from hot/cold radiators Calibrate detector output in input power units Calibrate detector output in input power units Determine the background noise Determine the background noise Block connect the detector beam to as little background – possible Block connect the detector beam to as little background – possible Measure time trace and using responsively and integration time express it in NEP Wt/Hz 1/2 Measure time trace and using responsively and integration time express it in NEP Wt/Hz 1/2