Integrated superconducting spectrometers (ISSs) for wideband sub-mm astronomy utilise quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems ...is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires accurate alignment of the laser to the sub-mm beam coming from the instrument, which is not always guaranteed to a sufficient accuracy. We develop an alignment strategy for wideband ISSs directly utilising the sub-mm beam of the wideband ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wideband ISS. We measure misalignment in a quasi-optical system operating at sub-mm wavelengths using a novel phase and amplitude measurement scheme, capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the MKID detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we follow a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns are taken across a harmonic range between 205 and 391 GHz and simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the sub-mm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.
Understanding telescope pointing (i.e., line of sight) is important for observing the cosmic microwave background (CMB) and astronomical objects. The Moon is a candidate astronomical source for ...pointing calibration. Although the visible size of the Moon (\(\ang{;30}\)) is larger than that of the planets, we can frequently observe the Moon once a month with a high signal-to-noise ratio. We developed a method for performing pointing calibration using observational data from the Moon. We considered the tilts of the telescope axes as well as the encoder and collimation offsets for pointing calibration. In addition, we evaluated the effects of the nonuniformity of the brightness temperature of the Moon, which is a dominant systematic error. As a result, we successfully achieved a pointing accuracy of \(\ang{;3.3}\). This is one order of magnitude smaller than an angular resolution of \(\ang{;36}\). This level of accuracy competes with past achievements in other ground-based CMB experiments using observational data from the planets.
We present a feasibility study for the high-redshift galaxy part of the Science Verification Campaign with the 220-440 GHz DESHIMA 2.0 integrated superconducting spectrometer on the ASTE telescope. ...The first version of the DESHIMA 2.0 chip has been recently manufactured and tested in the lab. Based on these realistic performance measurements, we evaluate potential target samples and prospects for detecting the CII and CO emission lines. The planned observations comprise two distinct, but complementary objectives: (1) acquiring spectroscopic redshifts for dusty galaxies selected in far-infrared/mm-wave continuum surveys; (2) multi-line observations to infer physical conditions in dusty galaxies.
We present a lab-on-chip experiment to accurately measure losses of superconducting microstrip lines at microwave and sub-mm wavelengths. The microstrips are fabricated from NbTiN, which is deposited ...using reactive magnetron sputtering, and amorphous silicon which is deposited using plasma-enhanced chemical vapor deposition (PECVD). Sub-mm wave losses are measured using on-chip Fabry-P{é}rot resonators (FPR) operating around \(350\ \)GHz. Microwave losses are measured using shunted half-wave resonators with an identical geometry and fabricated on the same chip. We measure a loss tangent of the amorphous silicon at single-photon energies of \(\tan\delta =3.7\pm0.5\times10^{-5}\) at \(6\ \)GHz and \(\tan\delta = 2.1\pm 0.1\times10^{-4}\) at \(350\ \)GHz. These results represent very low losses for deposited dielectrics, but the sub-mm wave losses are significantly higher than the microwave losses, which cannot be understood using the standard two-level system loss model.
DESHIMA 2.0 is a spectrometer for astronomical applications targeting sources at sub-mm wavelengths from 240GHz to 720GHz. The design for its wide band Quasi-Optical system was presented in the ...previous works. In this work, the experimental validation of the beam pattern of the system at the lower end of its frequency band is presented. The measurement for the complete frequency band of the system is ongoing and will be presented at the conference.
A superconducting on-chip microstrip filter bank spectrometer prototype for Far-Infrared (FIR) Astronomy is presented. The measurements showcase its capabilities towards moderate spectral resolution ...( f/\Delta f\sim 500 ) broadband FIR spectroscopy. In this sub-mm-wave filter bank, each spectral channel consists of an "I-shaped" microstrip THz bandpass filter that couples the radiation to a Microwave Kinetic Inductance Detector (MKID) for a background limited detection and a scalable frequency-multiplexed microwave readout.
The design of an octave bandwidth sub-mm wave superconducting on-chip filter-bank spectrometer for Astronomy is presented. An array of THz band-pass filters subdivides the bandwidth 220-440 GHz into ...channels with a spectral resolution of 400 and an average maximum coupling strength f/Δf of 40%. The filter-bank performance is assessed by means of a transmission line formalism that approximates its behavior. The chip is under fabrication and its measurements will follow.
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