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AMKID -- a large KID-based camera at the APEX telescope

N. Reyes, A. Weiss, S. J. C. Yates, A. M. Baryshev, I. C. mara-Mayorga, S. Dabironezare A. Endo, L. Ferrari, A. Görlitz, G. Grutzeck, R. Güsten, C. Heiter, S. Heyminck, S. Hochgürtel, H. Hoevers, S. Jorquera, A. Kovàcs, D. Koopmans, C. König, N. Llombart, K. M. Menten, V. Murugesan, M. Ridder, A. Schmitz, D. J. Thoen, A. J. van der Linden, L. Wang, O. Yurduseven, J. J. A. Baselmans, B. Klein

TL;DR

AMKID presents a large, kilo-pixel, KID-based camera for APEX that achieves dual-band, wide-field submillimeter imaging with high sensitivity and angular resolution. By employing NbTiN-Al hybrid MKIDs, lens-antenna coupling, and 4–8 GHz frequency-division multiplexing, AMKID attains a substantial field of view (15.3'×15.3') and a high detector count across two bands (LFA and HFA). Commissioning shows the LFA delivering NET ≈ 2.2 mK√s and mapping speeds competitive with or surpassing previous facilities, with on-sky sensitivities around 70–90 mJy√s per beam; the HFA is progressing toward full dual-band science operation with planned optics and readout upgrades. The instrument’s performance, including optics coupling, detector yield, and readout stability, supports transformative science in disk studies, galaxy evolution, and star-forming environments, while outlining clear paths for improvement in the HFA channel and readout architecture. AMKID thus represents a significant step toward fast, wide-field submillimeter surveys at APEX."

Abstract

The thermal emission at sub-millimeter wavelengths carries unique information in many astronomical applications ranging from disks and planet formation around young stars, to galaxy evolution studies at cosmological distances. Advancing on the mapping speed to detect this faint emission in ground-based astronomy has been a technical challenge for decades. The APEX Microwave Kinetic Inductance Detector (AMKID) camera was designed to accomplish this task. The instrument is a wide field-of-view camera based on kinetic inductance detectors. It is installed on the 12~meter APEX telescope in Chile at 5.100~meters above see level. The instrument operates dual color, covering simultaneously the 350~GHz and 850~GHz atmospheric windows. It has a large field-of-view of 15.3'x15.3', and an unprecedented number of pixels: 13.952~detectors in the high frequency band and 3.520~detectors in the low frequency band. Here we present a complete description of the instrument design and construction together with results of the successful low frequency array (LFA) commissioning campaign executed during the last year. The LFA performance is in good agreement with design parameters, with detector sensitivity of 2.2~mK$\sqrt{s}$ and diffraction limited beam sizes of 17.0''. On-sky measurements demonstrate a sensitivity of 70-90~mJy$\sqrt{s}$ per detector when operating under good atmospheric conditions (PWV below 1.0mm). With this performance the LFA regularly achieve a mapping sensitivity of 25~mJy when mapping a square degree in an hour. AMKID on APEX with its dual color observing capabilities, high sensitivity, large field-of-view and high angular resolution holds the promise to open a new range of science with the APEX telescope.

AMKID -- a large KID-based camera at the APEX telescope

TL;DR

AMKID presents a large, kilo-pixel, KID-based camera for APEX that achieves dual-band, wide-field submillimeter imaging with high sensitivity and angular resolution. By employing NbTiN-Al hybrid MKIDs, lens-antenna coupling, and 4–8 GHz frequency-division multiplexing, AMKID attains a substantial field of view (15.3'×15.3') and a high detector count across two bands (LFA and HFA). Commissioning shows the LFA delivering NET ≈ 2.2 mK√s and mapping speeds competitive with or surpassing previous facilities, with on-sky sensitivities around 70–90 mJy√s per beam; the HFA is progressing toward full dual-band science operation with planned optics and readout upgrades. The instrument’s performance, including optics coupling, detector yield, and readout stability, supports transformative science in disk studies, galaxy evolution, and star-forming environments, while outlining clear paths for improvement in the HFA channel and readout architecture. AMKID thus represents a significant step toward fast, wide-field submillimeter surveys at APEX."

Abstract

The thermal emission at sub-millimeter wavelengths carries unique information in many astronomical applications ranging from disks and planet formation around young stars, to galaxy evolution studies at cosmological distances. Advancing on the mapping speed to detect this faint emission in ground-based astronomy has been a technical challenge for decades. The APEX Microwave Kinetic Inductance Detector (AMKID) camera was designed to accomplish this task. The instrument is a wide field-of-view camera based on kinetic inductance detectors. It is installed on the 12~meter APEX telescope in Chile at 5.100~meters above see level. The instrument operates dual color, covering simultaneously the 350~GHz and 850~GHz atmospheric windows. It has a large field-of-view of 15.3'x15.3', and an unprecedented number of pixels: 13.952~detectors in the high frequency band and 3.520~detectors in the low frequency band. Here we present a complete description of the instrument design and construction together with results of the successful low frequency array (LFA) commissioning campaign executed during the last year. The LFA performance is in good agreement with design parameters, with detector sensitivity of 2.2~mK and diffraction limited beam sizes of 17.0''. On-sky measurements demonstrate a sensitivity of 70-90~mJy per detector when operating under good atmospheric conditions (PWV below 1.0mm). With this performance the LFA regularly achieve a mapping sensitivity of 25~mJy when mapping a square degree in an hour. AMKID on APEX with its dual color observing capabilities, high sensitivity, large field-of-view and high angular resolution holds the promise to open a new range of science with the APEX telescope.

Paper Structure

This paper contains 25 sections, 17 equations, 19 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Instrument Overview
  3. Detector technology
  4. Characterization of the detector arrays
  5. Optical system
  6. Cryogenic system
  7. Filter stack
  8. Filter self-heating model
  9. Read-out system
  10. Data processing and calibration
  11. Tone list generation and blind tone correction
  12. Circle calibration, frequency sweep and linearization
  13. Temperature calibration
  14. Instrument performance
  15. Array sensitivity
  16. ...and 10 more sections

Figures (19)

  • Figure 1: Atmospheric transmission at the Chajnantor Plateau. Normal condition of 1.0mm PWV is regularly observed during several months of a year. Outstanding conditions, below 0.5 mm PWV, are available on average during 890 hours per year. In the same plot we show the AMKID filter-stack transmission for the two arrays, and the Ruze efficiency of a 15-20 $\mu$m RMS surface quality telescope, typical value measured via holography at APEX.
  • Figure 2: (a) Optical micrograph of a single H-band detector with a zoom-in of the antenna structure. (b) Cross section of the chip-lens array assembly. All indicated parameters in panels (a) and (b) are given for both H-band and L-band in table \ref{['TableDesigns']}.
  • Figure 3: (a) Laboratory frequency sweep of the LT092/LFA4 detector chip, looking at a 300 K load. (b) Measured Q factors, note the sligth downward slope with frequency. (c) Histogram of the transmission of the KID resonances at their center frequency.
  • Figure 4: Schematic of the AMKID optics system. It consists of 6 reflective mirrors which have an overall magnification of 3.6. Only optical rays of the central pixel are shown.
  • Figure 5: (a) KID detector assembly during installation. The filter stack is removed from the assembly. Therefore, the two detectors are clearly visible in the image. The four temperatures stages are compactly assembled via a hexapod structure. (b) Cut view of the AMKID cryostat. HFA polarization is perpendicular to image plane. LFA array is located above the presented sagittal section. (c) Photography of the assembly and cabling process.
  • ...and 14 more figures