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CMB detectors & readout and how to model them in data analysis

Tijmen de Haan (KEK)

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2025/01/29

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Detector Classes

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calorimeters

bolometers

 

 

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The most important performance metric for CMB bolometers is noise.

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2025/01/29

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Detector counts have been increasing rapidly.

Tijmen de Haan (KEK)

2025/01/29

Ground-based CMB experiments have been rapidly increasing TES count

COBE (launched 1989):�7 detectors (1 bolometer)

WMAP (launched 2001):�20 detectors (no bolometers)

Planck (launched 2009): �96 detectors (52 bolometers)

LiteBIRD (launch in 2030s): ~5000 TES bolometers

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Detector & Optical coupling technologies��Optical coupling: “turn photon signal into electron signal”�a few mm-wave experiments (not comprehensive)

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2025/01/29

CCAT-prime/TolTEC/BLAST-TNG�(LEKID @ NIST)

GroundBIRD (MKID @ SRON)

QUIJOTE (HEMT @ IAC/IFCA)

BICEP/Keck/SPIDER (TES+phased array @ JPL)

ABS/ACTpol/SPTpol (TES+OMT/horn @ NIST)

SA/SPT-3G (TES+sinuous/lenslet @ ANL/Berkeley)

Planck HFI (NTD+horn @ JPL)

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Modeling the TES: power balance equation

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Tijmen de Haan (KEK)

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2025/01/29

“island”�Heat Capacity C�Temperature T

Weak thermal conductance G

Thermal bath Tbath�

TES Resistance R�TES Bias Pelectrical

Input Power Poptical

R

T

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MKIDs

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2025/01/29

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Detectors & Optical Coupling

  • Heterodyne penalty encourages the use of bolometers for CMB at >90 GHz: MKID & TES.
  • TESs are currently the most popular.
  • Some think that MKIDs will replace TESs due to their
    • nature as resonators: they are intrinsically compatible with microwave multiplexing readout.
    • simpler fabrication compared to TES.
  • In my experience, decisions on which technology to use often come down to programmatic and practical decisions.
    • Institutional & individual experience
    • Heritage (confidence) vs novelty (fun)

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2025/01/29

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Tijmen de Haan (KEK)

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2025/01/29

Multiplexed TES Readout technologies

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Detector arrays are generally too large for single-detector readout -> need multiplexing

tMux

  • DC-bias mOhm TES
  • Rapidly switch which TES is being read using using SQUIDs as switches
  • SQUID array as first stage amplifier

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fMux

  • AC-bias Ohm TES
  • Each TES in series with LC resonator
  • SQUID array as first stage amplifier

 

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Feedback

  • A common technique for linearizing or stabilizing a detector or readout component is feedback.

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  • Simple example:

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  • More complex example:

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  • There is potential for further enhancing readout with new forms of feedback.

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2025/01/29

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Let’s compare multiplexed readout technologies. �(Just my opinion)

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2025/01/29

Multiplexing�Technology

Time domain

Frequency domain

Code domain

Microwave

Maturity

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Sensitivity to environment

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Cryogenic power dissipation

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Room temperature power usage

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Complexity

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Promise / room for improvement

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Unique benefit

Largest number of successful experiments in the field

Relatively light on nanofabrication requirements

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Very high mux factors

😃

🙂

😔

😭

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Detector Modeling: two perspectives

Hardwave Perspective

  • Photons come in from the sky
  • Photon signal is converted to an electronic signal using a nonlinear detector
  • We use nonlinear devices to amplify and multiplex the signal
  • There are several stages of amplification
  • The signal is digitized and downsampled
  • The readout system usually applies 1-3 layers of analog/digital/mixed feedback to linearize/stabilize the detector+readout system.
  • External factors such as ambient magnetic field, EMI, grounding, temperature.
  • Conclusion: we have an excellent understanding of the non-linear, non-stationary, non-bijective mapping that relates the sky signal to what you actually measure.

Tijmen de Haan (KEK)

12

2025/01/29

 

Hardware-agnostic analysis is perfectly fine as long as the loss in sensitivity and induced systematic errors are sufficiently small.

We understand the detectors & readout well. There is information here we can use in analysis if necessary.

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Beyond Calibration: Hardware-Agnostic Techniques

  • Example 1: correct time dependence of calibration by frequent recalibration using a thermal calibrator behind a small hole in the secondary mirror.

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  • Example 2: correct elevation dependence of calibration at the map level

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2025/01/29

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Beyond Calibration: Hardware-aware Inverse Modeling

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2025/01/29

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Summary

  • I’ve summarized some of the popular technologies for optical coupling, detectors, and readout.
  • These systems are sophisticated.
  • Hardware experts generally understand these systems.
  • As requirements on systematic errors continue to get more stringent, analysis experts will increasingly need to rely on this knowledge.

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Tijmen de Haan (KEK)

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2025/01/29