Accurate sky signal reconstruction for ground-based spectroscopy with kinetic inductance detectors

Abstract

Context. Wide-field spectrometers are needed to deal with current astrophysical challenges that require multiband observations at millimeter wavelengths. An example of these is the KIDs Interferometer Spectrum Survey (KISS), which uses two arrays of kinetic inductance detectors (KIDs) coupled to a Martin-Puplett interferometer (MPI). KISS has a wide instantaneous field of view (1 deg in diameter) and a spectral resolution of up to 1.45 GHz in the 120-180 GHz electromagnetic band. The instrument is installed on the 2.25 m Q-U-I JOint TEnerife telescope at the Teide Observatory (Tenerife, Canary Islands), at an altitude of 2 395 m above sea level. Aims. This work presents an original readout modulation method developed to improve the sky signal reconstruction accuracy for types of instruments for which a fast sampling frequency is required, both to remove atmospheric fluctuations and to perform full spectroscopic measurements on each sampled sky position. Methods. We first demonstrate the feasibility of this technique using simulations. We then apply such a scheme to on-sky calibration. Results. We show that the sky signal can be reconstructed to better than 0.5 % for astrophysical sources, and to better than 2 % for large background variations such as in "skydip", in an ideal noiseless scenario. The readout modulation method is validated by observations on-sky during the KISS commissioning campaign. Conclusions. We conclude that accurate photometry can be obtained for future KID-based interferometry using the MPI.

CONCERTO : Digital processing for finding and tuning LEKIDs

“…• 𝑝 1 (𝐼 1 ;𝑄 1 ) : 32 positive modulation points at 𝐹 𝑡𝑜𝑛𝑒 = 𝐹 0 + 𝐹 𝑚𝑜𝑑 • 𝑝 2 (𝐼 2 ;𝑄 2 ) : 32 negative modulation points at 𝐹 𝑡𝑜𝑛𝑒 = 𝐹 0 -𝐹 𝑚𝑜𝑑 • 𝑝 3 (𝐼 3 ;𝑄 3 ) : 1472 unmodulated observation points at 𝐹 𝑡𝑜𝑛𝑒 = 𝐹 0 For CONCERTO 𝐹 𝑚𝑜𝑑 is generally set at about 10 kHz. The modulation scheme can be used both for calibration purposes (see [5]) and to ensure that the LEKID response is correctly sampled at the resonance frequency. In this regard and for the sake of simplicity, we consider here three main cases as shown in figure 5.…”

“…Then, during observation data are taken with the frequency tones fixed to the values obtained from the . The procedure is based on the calibration procedure presented in [5] and was also used for the KISS experiment [3]. As illustrated in figure 12 we first estimate a calibration coefficient, 𝐶, by From 𝜃 12 = arctan 𝐼 0 −𝐼 12 𝑄 0 −𝑄 12 we define Δ𝜃 = 𝜃 2 − 𝜃 1 with 𝑝 0 = (𝐼 0 , 𝑄 0 ) the center of the resonance circle.…”

CONCERTO: a breakthrough in wide field-of-view spectroscopy at millimeter wavelengths

“…In ground-based experiments, the fast sampling of the interferograms is crucial to deal with the atmospheric fluctuations and properly calibrate the signal. 9 In addition, FTS allows us to exploit a larger instantaneous FoV with respect to other spectrometric solutions (e.g., grating or Fabry-Perot) or dispersive elements (prism or dichroic filters). In the FTS, the single-pixel detects the whole electromagnetic signal and records a full interferogram.…”

CONCERTO: readout and control electronics

“…front-end board. Both the KID_READOUT boards and MCMPM board possess this memory table so the modulation, which used for tuning [9] and scientific calibration [10], does not interfere with the interferometry measurement. For example, among the 4096 steps, only the first 64 steps are modulation samples leaving the rest for observation purpose.…”

“…This latter synchronization is required as the acquisition must be already running before starting mirror movements and we want the interferometer cycle to start just after the 3-point frequency modulation executed at each start of scan. Indeed this frequency modulation is mandatory before each interferogram acquisition as it allows to calibrate the KIDs response to a known frequency shift [10]. The frequency modulation is injected by the KID readout board which is synchronized with the same technique as described here.…”