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We present measurements and simulations of the polarization purity of leaky lens-antenna coupled microwave Kinetic Inductance Detectors (KIDs) at 1.5 THz. We find the integrated cross-polarization level to be at -21.5 dB for 1 f\#$\lambda$ spatial sampling. The measurements agree well with the theoretical description which is based on a combination of in-transmission simulation of the antenna feed, and an in-reception analysis of the antenna-KID system. Combined with the measured noise equivalent power of 5--7$\times$10$^{-20}$ W/$\sqrt{\mathrm{Hz}}$, these detectors are excellent candidates for large scale and high performance imaging polarimetric instruments., Comment: This work has been submitted to IEEE Transactions of THz Science and Technology for possible publication

Detector requirements for far infrared astronomy generally result in devices which exhibit a few-moded response to incident radiation. The sensitivity and spatial form of the individual modes to which such a detector is sensitive can be determined with knowledge of the complex valued cross-spectral density of the system, which we label the detector response function (DRF). A matrix representing the discretized cross-spectral density can be measured from the complex amplitudes of interference fringes generated by two identical sources as they are independently scanned through the field of view. We provide experimental verification of this technique using monochromatic THz beams generated by photomixers in which the relative phase is varied with fiber stretchers. We use this system to characterize the modal response of a single pixel from an array of microwave kinetic inductance detectors (MKIDs)., Comment: in IEEE Transactions on Terahertz Science and Technology. 2023

Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220-440 GHz band in a single shot, corresponding to a redshift range of $z$=3.3-7.6 for the ionized carbon emission ([C II] 158 $\mu$m). The first-light experiment of DESHIMA 1.0, using the 332-377 GHz band, has shown an excellent agreement among the on-sky measurements, the lab measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign., Comment: 9 pages, 4 figures, 1 table, accepted for publication in the Journal of Low Temperature Physics for the LTD19 special issue

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter-bank and Microwave Kinetic Inductance Detector (MKID) to investigate dusty star-burst galaxies in the distant universe at millimeter and submillimeter wavelength. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV, 0.4-3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of $1\sigma=4$%, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs, and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array., Comment: Accepted for publication in the Journal of Low Temperature Physics for LTD-18 special issue

We present the design, fabrication and characterisation of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute coupling efficiency at three frequency bands centred around 350, 650 and 850 GHz, covering the full antenna band. We find an aperture efficiency $\eta_{ap} \approx 0.4$ over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the sub-mm wavelength range for future on-chip spectrometers., Comment: Accepted for Publication at IEEE Transactions on Antennas and Propagation

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/\Delta F \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible., Comment: Published in Nature Astronomy. SharedIt Link to the full published paper: https://rdcu.be/bM2FN

Terahertz spectrometers with a wide instantaneous frequency coverage for passive remote sensing are enormously attractive for many terahertz applications, such as astronomy, atmospheric science and security. Here we demonstrate a wide-band terahertz spectrometer based on a single superconducting chip. The chip consists of an antenna coupled to a transmission line filterbank, with a microwave kinetic inductance detector behind each filter. Using frequency division multiplexing, all detectors are read-out simultaneously creating a wide-band spectrometer with an instantaneous bandwidth of 45 GHz centered around 350 GHz. The spectrometer has a spectral resolution of $F/\Delta F=380$ and reaches photon-noise limited sensitivity. We discuss the chip design and fabrication, as well as the system integration and testing. We confirm full system operation by the detection of an emission line spectrum of methanol gas. The proposed concept allows for spectroscopic radiation detection over large bandwidths and resolutions up to $F/\Delta F\sim1000$, all using a chip area of a few $\mathrm{cm^2}$. This will allow the construction of medium resolution imaging spectrometers with unprecedented speed and sensitivity., Comment: 21 pages, 7 figures

Complex field measurements are increasingly becoming the standard for state-of-the-art astronomical instrumentation. Complex field measurements have been used to characterize a suite of ground, airborne, and space-based heterodyne receiver missions [1], [2], [3], [4], [5], [6], and a description of how to acquire coherent field maps for direct detector arrays was demonstrated in Davis et. al. 2017. This technique has the ability to determine both amplitude and phase radiation patterns from individual pixels on an array. Phase information helps to better characterize the optical performance of the array (as compared to total power radiation patterns) by constraining the fit in an additional plane [4]. Here we discuss the mathematical framework used in an analysis pipeline developed to process complex field radiation pattern measurements. This routine determines and compensates misalignments of the instrument and scanning system. We begin with an overview of Gaussian beam formalism and how it relates to complex field pattern measurements. Next we discuss a scan strategy using an offset in z along the optical axis that allows first-order optical standing waves between the scanned source and optical system to be removed in post-processing. Also discussed is a method by which the co- and cross-polarization fields can be extracted individually for each pixel by rotating the two orthogonal measurement planes until the signal is the co-polarization map is maximized (and the signal in the cross-polarization field is minimized). We detail a minimization function that can fit measurement data to an arbitrary beam shape model. We conclude by discussing the angular plane wave spectral (APWS) method for beam propagation, including the near-field to far-field transformation.

With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled., Comment: arXiv admin note: substantial text overlap with arXiv:1707.02142

Large ultra-sensitive detector arrays are needed for present and future observatories for far infra-red, submillimeter wave (THz), and millimeter wave astronomy. With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves, the surface wave. We demonstrate this effect with focal plane arrays of 880 lens-antenna coupled Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field measurements of the MKID optical response versus the position on the array of a reimaged optical source. We demonstrate that the optical response of a detector in these arrays saturates off-pixel at the $\sim-30$ dB level compared to the peak pixel response. The result is that the power detected from a point source at the pixel position is almost identical to the stray response integrated over the chip area. With such a contribution, it would be impossible to measure extended sources, while the point source sensitivity is degraded due to an increase of the stray loading. However, we show that by incorporating an on-chip stray light absorber, the surface wave contribution is reduced by a factor $>$10. With the on-chip stray light absorber the point source response is close to simulations down to the $\sim-35$ dB level, the simulation based on an ideal Gaussian illumination of the optics. In addition, as a crosscheck we show that the extended source response of a single pixel in the array with the absorbing grid is in agreement with the integral of the point source measurements., Comment: accepted for publication in IEEE Transactions on Terahertz Science and Technology