The TolTEC Camera, mounted on the Large Millimeter Telescope (LMT), is a 3-band continuum camera and polarimeter operating at millimeter wavelengths. This paper reviews our progress on the camera commissioning and its inaugural scientific programs, spanning the 2022/2023 commissioning phases and reviewing the winter 2024 science program. We report on mapping speed estimations, optical performance, and the first scientific imaging and polarimetry findings. Additionally, advancements in out-of-focus holography and the integration of two novel maximum likelihood mapmakers are discussed. We conclude with scientific forecasts for the first four TolTEC Legacy Surveys and an overview of the initiatives aimed at facilitating public access to the camera and the broader LMT infrastructure.

Microwave kinetic inductance detectors (MKIDs) are increasingly used in ground-based (sub)millimeter-wave astronomy experiments. Two existing challenges to operating detector arrays remain in selecting excitation tones for each MKID where there are hundreds of resonators on the same feedline or network and that will yield the best combination of linearity and sensitivity. This is further complicated when operating arrays at ground-based telescopes, where variations in background loading from the atmosphere can induce significant shifts in MKID resonant frequencies and affect quality factors. We describe a quantitative method for optimal tuning of MKID arrays under dynamic loading conditions. We apply this new readout tuning technique to the 1.1 mm MKID array of the TolTEC camera at the Large Millimeter Telescope, where we incrementally change the readout power applied to investigate its effect. We perform in lab optical characterization of a CCAT Observatory MKID array to investigate optimal tuning under different loading conditions.

The BLAST Observatory is a proposed super-pressure balloon-borne submillimeter polarimeter designed for a future ultra-long duration balloon campaign from Wanaka, New Zealand. BLAST Observatory will have a 1.8m modified off-axis Gregorian optical system coupled to a 300L ^4He cryogenic receiver with 8,274 microwave kinetic inductance detectors (MKIDs) cooled to 100mK by an adiabatic demagnetization refrigerator (ADR) backed by a ^3He sorption refrigerator at 300mK and a liquid helium pumped pot operating at 2K. The detector readout will utilize a new Xilinx RFSOC-based system. With this instrument we aim to answer outstanding questions about interstellar dust dynamics and star formation as well as provide community access to the polarized submillimeter sky. The BLAST Observatory is designed for a minimum 31-day flight of which 70% will be dedicated to observations for BLAST scientific goals and the remaining 30% will be open to proposals from the wider astronomical community through a shared-risk proposals program. We will present the overall instrument design, current status, and recent progress with the optical design and metrology strategy.

The Simons Observatory is a ground-based cosmic microwave background (CMB) survey experiment consisting of three 0.5 m small-aperture telescopes (SATs) and one 6 m large-aperture telescope (LAT), located at 5200 m elevation in the Chilean Atacama Desert. The LAT contains the 2.4 m diameter Large Aperture Telescope Receiver (LATR) and its 13 Optics Tubes with more than 62,000 Transition Edge Sensor (TES) detectors spanning six frequency bands between 27 GHz and 280 GHz. Once complete, SO will be the largest and most capable CMB observatory ever built, producing arcminute resolution maps over half of the microwave sky with unprecedented sensitivity. Extensive assembly, integration, and testing work was required to successfully deploy and commission the SO LAT and LATR, with first light expected before the end of 2024. Here we provide a detailed look at the deployment, commissioning, and operation status of the SO LAT and LATR.

We present the laboratory performance of a 1,704-detector microwave SQUID multiplexed (μmux) Transition-Edge Sensor (TES) array and its accompanying RFSoC-based readout electronics after integration with AliCPT-1: a 72-cm aperture, two-lens refracting CMB polarization telescope, which will observe from the Tibetan Plateau beginning in 2024.

The first AliCPT-1 module incorporates two 4-6 GHz μmux readout lines, each with a multiplexing factor of 910, to readout 1,704 TES bolometers and additional dark channels. The module is probed via an RFSoC-based room-temperature electronics system, which combines all tone generation and processing procedures on a single piece of hardware.

Here we describe the integration of the module and electronics with the receiver and conduct end-to-end laboratory testing of their performance. Module measurements include spectra, optical efficiency, polarization efficiency, near-field beam maps, and sensitivity to external magnetic fields. We evaluate the behavior of the readout system during optical data collection, including its noise performance.

LiteBIRD is a next-generation space telescope which aims to measure primordial gravitational waves in the polarisation of the cosmic microwave background. The level of the primordial (tensor, or B-mode) signal in relation to the scalar (or E-mode) only has a known upper limit, and the instrument requirement is to measure a tensor-to-scalar ratio sensitivity δr<0.001. Systematic effects arising from cosmic radiation are expected to play a significant role, and our prior work has focused on the development of an end-to-end simulation tool for evaluating the scale of this in LiteBIRD’s Low Frequency Telescope (LFT). We present an updated forecasting method which makes use of event tables generated by a new Geant4 mass model of LFT. We will compare the previously used simplified model with that of the updated mass model, and project these differences into an expected effect of the cosmic ray effect δr. Lastly, we will examine the use of a simple filtering method for removing direct detector impacts by cosmic rays, which have been shown previously to play the largest role in this systematic effect.

Measurements of B-mode polarization in the cosmic microwave background (CMB) sourced from primordial gravitational waves would provide information on the energy scale of inflation and its potential form. To achieve these goals, one must carefully characterize the Galactic foregrounds, which can be distinguished from the CMB by conducting measurements at multiple frequencies.

BICEP Array (BA) is the latest generation multi-frequency instrument of the BICEP/Keck program, which specifically targets degree-scale primordial B-modes in the CMB. In its final configuration, BA will consist of four small-aperture receivers, spanning six different frequency bands. The BA4 receiver is designed to characterize Galactic dust at 220/270 GHz. This receiver is currently undergoing commissioning at Stanford and is scheduled to deploy to the South Pole during the 2024-2025 austral summer. Here, we will provide an overview of this high frequency receiver, discussing the integration status and test results as it is being commissioned.

We present a plan for sub/millimeter-wave line intensity mapping (LIM) using an imaging spectrograph based on the Terahertz Integral Field Units with Universal Nanotechnology (TIFUUN) architecture. We aim to measure the dust-enshrouded cosmic star formation rate density within the first 2 billion years by conducting LIM observations of ionized carbon [C II] 158 μm and oxygen [O III] 88 μm lines, redshifted to sub/millimeter wavelengths. The proposed imaging spectrograph will simultaneously observe two frequency bands: Band-1 (139-179 GHz) and Band-2 (248-301 GHz). Each band will feature up to ∼100 imaging pixels (spaxels), with each spaxel having 100 spectral channels, providing a modest spectral resolution (R~500). The total number of detectors (voxels) will reach ~20,000. This dual-band configuration will allow simultaneous measurement of key spectral lines, e.g., [C II] 158 μm and [O III] 88 μm lines at z = 10.2 - 12.6, and CO(4-3), (7-6), [C I](1-0) and (2-1) at z = 1.9 - 2.2, enabling cross-correlation analysis. We will develop data-scientific methods to remove atmospheric noise using sparse modeling and to extract signals from the observed data using deep learning.

Scalable, densely packed spectrometer arrays (integral field units, or IFUs) would enable intensity mapping sensitive enough for precision measurements of cosmology and astrophysics in a new redshift regime. This scalability requires a new architecture, with spectrometers oriented parallel with incident light.

The key technology required is an inline waveguide-to-coplanar-waveguide transition. We present a millimeter-wave IFU concept that includes this new transition with on-chip kinetic-inductance-based spectrometers. The transition was designed with efficient Bayesian optimization and made robust to manufacturing tolerance with a novel optimization algorithm. It has >95% coupling over an octave bandwidth for 95% of randomly sampled transitions within tolerance. The design approach is of general interest to many instrument design problems; a Python implementation of the algorithm alongside an extension that automates a widely-used mesh-based EM solver are made publicly available. We also present the status of our efforts to fabricate transition prototypes in the 85--170 GHz band.

We present a thermal kinetic inductance detector array design for CMB polarization observation at 90/150 GHz bands. A horn-coupled planar ortho-mode transducer is used for a broadband linear polarization separation. The frequency separation is done using a fast roll-off lumped-element diplexer. Thermal kinetic inductance detectors with Al is used as the detector. The array has more than 450 optical pixels with more than 1800 detectors. The array design and preliminary measurement results will be discussed.

The payload module (PLM) of the next-generation CMB satellite LiteBIRD features three telescopes: a crossed-Dragone reflective Low-Frequency Telescope (LFT), and on-axis refractive Mid- and High-Frequency Telescopes (MFT and HFT), spanning 15 unique frequency bands from 34 to 448 GHz.

Central to the PLM are Transition Edge Sensor (TES) bolometers, maintained at a bath temperature of ~110 mK. They are coupled to the sky with silicon lenslets with metamaterial anti-reflection surfaces (LFT and MFT) and platelet-based horns (HFT). The cryogenic and room-temperature electronics translate the tiny thermal signals from TES bolometers into digital data at 18 GB/day. The PLM thermal management utilizes passively and actively cooled V-grooves and a series of coolers including a space-grade adiabatic demagnetization refrigerator. Polarization is modulated by continuously rotating achromatic half-wave plates held at around 10 K.

This design focuses on reducing systematic errors and enhancing stability. Combining systematic uncertainties, a statistical uncertainty of 2.2μK-arcmin in polarization, and margin, we will achieve a δr=0.001 precision on the tensor-to-scalar ratio r.

We present preparation for fabrication and deployment of science-grade kilo-pixel Kinetic Inductance Detector (KID) based arrays for the Terahertz Intensity Mapper (TIM). TIM is a NASA-funded balloon-borne experiment planning its Antarctic flight for 2026. TIM employs two focal planes, each with four subarrays of ~900 hexagonal-packed, horn-coupled aluminum KIDs. Fabrication yield is high, and we have successfully mapped KID resonant frequencies to spatial locations with our LED mapper. The spatial and frequency information associated with every yielded pixel allows a study of spatial coincidences as cosmic rays interact with the array, as well as interpretation of a covariance analyses performed on the noise timestreams. We also describe the improvement on the science-usable yield of our 864-pixel array achieved by (1) the lithographic trimming that de-collides resonators, and (2) our characterization of interpixel crosstalk. This pioneering work on the postprocessing will pave the way for science with our large KID arrays.

We present the first full-array optical characterizations of the 280 GHz aluminum-based superconducting microwave kinetic inductance detector (MKID) arrays developed at NIST, CO, USA for the CCAT Collaboration for observing galactic ecology, Sunyaev-Zel'dovich effect, galaxy evolution, and line intensity mapping. The main advantage of aluminum MKIDs is their lower 1/f noise compared to the alternative choice of titanium-nitride (TiN) MKIDs, which would reduce systematic drifts when mapping the sky. We will present the spectral response, polarization characteristics, detector efficiency, and noise equivalent power (NEP) under the relevant conditions for these detectors. Two aluminum and one TiN MKID arrays will form the detector arrays in the 280 GHz instrument module of the Prime-Cam. First light observations are expected in 2025.

Deposited dielectrics with low mm-submm loss will be of great benefit to on-chip superconducting circuits for mm-submm astronomy. Compared with planar chip designs, multilayer structures with deposited dielectrics allow for more compact circuit elements, and eliminate radiation losses at high frequencies. While recently hydrogenated amorphous silicon carbide has been demonstrated to exhibit low dielectric losses at mm-submm wavelengths, the origin of the mm-submm loss in hydrogenated amorphous silicon carbide remains unknown.

We measured the 270-600 GHz dielectric losses of hydrogenated amorphous silicon carbide in superconducting microstrip lines. Furthermore, we measured the complex dielectric constant of the hydrogenated amorphous silicon carbide in the 3-100 THz range using Fourier transform spectroscopy. We modeled the loss data from 0.27-100 THz using a Maxwell-Helmholtz-Drude dispersion model. Our results demonstrate that phonon modes above 10 THz dominate the mm-submm losses in deposited dielectrics.

The optical coupling of detectors to telescope optics is a challenge for future far-infrared astrophysics observatories. The PRobe far-Infrared Mission for Astrophysics (PRIMA) collaboration has developed monolithic silicon microlens arrays for superconducting detector arrays spanning wavelengths from 24 to 261 microns. These custom-microfabricated lens arrays meet the stringent surface accuracy and roughness requirements that are necessary at PRIMA’s shortest wavelengths. Grayscale lithography is used in combination with deep silicon plasma etching to create arrays of three-dimensional lens profiles. This fabrication process generates highly uniform and accurate microlenses across a roughly 80 by 10 millimeter 1008-element array. The kilopixel microlens arrays are bonded to matching PRIMA detector arrays with a thin and uniform layer of epoxy. In this presentation, we report on the status and performance of PRIMA’s microlens fabrication and microlens-detector array hybridization processes.

We develop polarimetric detector arrays for submillimeter Space astronomy. The technology is based on the all-silicon bolometer scheme established for the Herschel/PACS photometer. Each pixel detects two orthogonal polarization directions with an efficiency greater than 95%. Every other pixel in the array is rotated by 45° to retrieve the linear Stokes parameter of the incident light inside the Airy disc of the telescope optics. We reduced the temperature to 50 mK to improve sensitivity and introduced new readout schemes based on single or double Wheatstone bridge configurations for fully differential DC outputs. The detectors are grown directly on a CMOS circuit wafer to ensure the largest bandwidth with the highest response.

We design, fabricate, and measure a novel spectrometer based on meta-surface structures, aiming to optimize its spectroscopic resolution within a band from 1.7 to 2.5 THz. The latter corresponds to a bandwidth of 38%, being comparable with a grating spectrometer. The meta-surfaces apply unit cells that consist of double-anchor structures based on gold, polyimide and gold triple layers. Several quantum cascade lasers that operate at slightly different frequencies around 2.1 THz were used to validate the spectrometer. We have measured a resolving power R of 273 and an efficiency of 78 %. Our results demonstrate for the first time a centimeter-sized, light weight FIR spectrometer with a promising resolution, which has potential to replace the half meter-sized, heavy grating based spectrometers in this wavelength band.

The South Pole Telescope Summertime Line Intensity Mapper (SPT-SLIM) is a pathfinder instrument that will observe on the 10-m South Pole Telescope in the 2024-2025 austral summer. The instrument consists of 12 dual-polarization pixels spanning 120-180 GHz with an R = 200 filterbank spectrometer coupled to aluminum kinetic inductance detectors. These spectrometers will be deployed in a compact 100 mK cryostat, located to intercept the main beam of the SPT without disturbing the SPT-3G experiment. The SPT-SLIM frequency range will be sensitive to the carbon monoxide (CO) line emission from high-redshift galaxies, paving the way for future high-redshift cosmology experiments. I will summarize the cryostat, optical design and commissioning status, present detector performance, and discuss the deployment and observation plans for the 2024-2025 austral season.

Following the discoveries of the Herschel space telescope and the numerous observations in the submillimeter range of the interstellar medium (ISM), we are developing two cryogenic spectrometer concepts that can be integrated on a detector focal plane to understand the evolution of the various phases of the ISM. In this talk, we present the principle and measured performance of those two multi-wavelength Fabry-Perot. The first concept is an adjustable Fabry-Perot cavity with dielectric Bragg mirrors. This prototype, equipped with a piezoelectric mechanism is used to demonstrate the concept of a scanning Bragg mirror Fabry-Perot, enabling the spectrum around a line to be finely scanned without loss.

The second concept is a stationary array of Fabry-Perot made entirely of silicon. In this spectrometer, the cavity is made of microstructured silicon. By adjusting the size of the sub-wavelength structures, we change the optical index of the cavity and therefore the transmitted wavelength.

The Heterodyne Spectrometer Instrument (HSI) is one of two instruments designed for the recently submitted Far-IR Spectroscopy Space Satellite proposal to NASA. HSI stands out as the first heterodyne array receiver for a space mission. It covers a broad bandwidth range between 150 and 600 microns in just three bands, each equipped with two 5-pixel arrays. HSI facilitates dual-polarization, multi-pixel, and multi-frequency observations on a satellite, achieved through careful design and the utilization of low-heat dissipating, low-power, yet high TRL components. We provide details of the optical design and present a solution for thermal/background compatibility between the direct detector and heterodyne instrument.

Future observatories for the far-infrared (FIR), such as envisioned in the NASA Probe announcement, will offer unprecedented sensitivity by using cryogenically cooled optics. Large arrays of lens-absorber coupled Microwave Kinetic Inductance Detectors (MKIDs) are the only candidate to fulfill the requirements for these observatories, requiring unprecedented sensitivity with a noise equivalent power below 10^(-19) W/√Hz while operating up to 12THz. The incoherent coupling mechanism of distributed absorbers leads to a robustness against misalignment, assembly, and fabrication issues at FIR wavelengths. In this contribution, we will present the design and fabrication of large arrays of lens-absorber coupled detectors and evaluate their performance at 7 and 12THz and demonstrate an NEP of 0.7⋅10^(-19) W/√Hz.

We present the design and optical characterization of a novel highly compact three-dimensional microwave kinetic inductance detector (3D-MKID). At short wavelengths, such as the far- and mid-infrared, the pixel density of MKID arrays is often limited by the size and geometry of each resonator’s capacitor. Sending the non-optically active component of the resonator into the third dimension minimizes the footprint of each pixel, allowing much higher array densities to be achieved. In our 3D-MKID design, we compactify the resonator by conformally coating deep-etched holes in the silicon substrate with superconducting films formed by atomic layer deposition. The resulting geometry consists of three-dimensional coaxial transmission lines, which are then connected to a meandered absorber on the substrate surface. An array of these resonators are capacitively coupled to a microstrip feedline. We present the characterization of a prototype 3D-MKID array and compare it to simulate resonator properties. We additionally describe the detector sensitivity performance when illuminated by a far-infrared blackbody source.

We are developing broadband metamaterial planar lenslet arrays for millimeter and submillimeter imaging using stacked silicon wafers patterned with subwavelength copper squares, deep reactive ion etched (DRIE) holes, or a hybrid combination of the two. Beam-forming is accomplished through spatial variation in refractive index within each pixel created by these subwavelength features, a gradient-index (GRIN) design. However, the optical properties of both the metal mesh and DRIE metamaterials exhibit dependence on polarization orientation and wavelength, posing challenges for lens design. We combine metal mesh and DRIE GRIN sections to leverage the contrasting polarization- and frequency-dependent properties of the two material types. Here we present measurements of our most recent prototype metamaterial GRIN lens on sinuous antenna-coupled TES detectors from 88 to 225 GHz. We also present design studies extending to higher frequencies and optimizing for different pixel pitches.

The goal of the PolarKID project is testing a new method for the measurement of polarised sources, in order to identify all the possible instrumental systematic effects that could impact the detection of CMB B-modes of polarisation. It employs the KISS (KIDs Interferometer Spectrum Survey) instrument coupled to a sky simulator and to sources such as point-like black bodies (simulating planets), a dipole (extended source) and a polariser. We use filled-arrays Lumped Element Kinetic Inductance Detectors (LEKIDs) since they have multiple advantages when observing both in photometry and in polarimetry configuration.

We present measurements of a polarization sensitive lens-antenna coupled MKID array at 1.5THz, mounted with an additional 20dB neutral density filter in a wide field camera. This allows full end to end system characterization with room temperature optical sources, but under similar optical loading conditions as expected in a space based polarimeter configuration.

The system is characterized using a wideband polarized photomixer based phase and amplitude beam pattern setup at 1.5THz. Two separate measurements with orthogonal source polarizations enable the co and cross polarization to be extracted, showing the full system low cross-polarization needed for many future polarimetric applications. Such a measurement setup is additionally of potential interest for the characterization of future missions (for example in the Far Infra-Red): to obtain the optical beam quality and verifying the optical interfaces on a component/sub-component level. We present and discuss this setup and the characterization of the lens-antenna coupled MKID camera.

Next generation far infrared instrument proposals for space missions present some interesting and challenging optical filtering requirements. There is a combined need for: shorter wavelength (down to 20µm) FIR filters and dichroics tailored for observational band selection; tight control of bandwidths and rejection of out-of-band radiation; and instrument thermal control.

Here we review the current state of the art for these devices for applications shorter that 200 µm (low-pass, high-pass and band-pass filters, polarisers, dichroics and beam-dividers); we discuss current developments and technological limitations and present solutions for future FIR instrument concepts.

We present the on-sky commissioning and science verification of DESHIMA 2.0: the first science-grade integrated superconducting spectrometer (ISS) for ultra-wideband mm-submm spectroscopy. With an instantaneous band coverage of 205-392 GHz at a spectral resolution of F/dF = 500, DESHIMA 2.0 will be applied to emission line surveys and redshift measurement of dusty star-forming galaxies, spectroscopic Sunyaev–Zeldovich effect observations of galaxy-clusters, and other new science cases that utilize its ultra-wide bandwidth. Compared to its predecessor (DESHIMA 1.0), DESHIMA 2.0’s superconducting filterbank chip with a x4 higher optical efficiency, x4 wider instantaneous bandwidth, x20 faster position switching on the sky, and a remotely-controlled optics alignment system. DESHIMA 2.0 is currently installed on the ASTE 10-m telescope at 4860 m altitude with excellent sky transmission, and is being commissioned for science operation. In the conference we will report the on-sky performance and latest results in the science-verification campaign at ASTE.

Increasingly large arrays TES bolometers continue to be planned for future mm-wave observatories, but their scalability is limited by the associated cryogenic multiplexing readout. Microwave SQUID multiplexing is a natural candidate for future systems, as it already boasts a ~10x channel handling advantage over other readout schemes due to its large available bandwidth. By further doubling this bandwidth, the demonstration we present increases the multiplexing factor from the prior best of 910 to 1,820 and enables a simple 1:1 pairing of detector components and multiplexer hardware. We show a yield of greater than 80% based on TES IV curve quality and model typical nearest-neighbor crosstalk to be ~0.4%. Finally, we estimate from measurements that only 3% of the total noise budget would result from the multiplexer if installed in a typical sorption-cooled ground-based receiver observing 60 degrees above the horizon with a zenith precipitable water vapor of 1.3 mm.

Kinetic inductance traveling-wave parametric amplifiers (KI-TWPA) offer wide instantaneous bandwidth, quantum noise limited performance, and high dynamic range, making them suitable for use in the readout of cryogenic detectors and superconducting qubits and a variety of applications in quantum sensing. This work discusses the design, fabrication, and measurements of a four-wave mixing microstrip KI-TWPA operating in the 4 - 8 GHz band. This frequency band is commonly used to read out cryogenic detectors such as microwave kinetic inductance detectors (MKIDs) and superconducting Josephson junction-based qubits. We report a measured gain of over 15 dB using four-wave mixing with a high dynamic range in the 4 - 8 GHz band. We also show the tunability of bandwidth by setting the pump-tone condition. Using a Y-factor method, we measure a near quantum limit KI-TWPA added noise in the 4 - 8 GHz band.

We present the design and testing of spaceflight multiplexing kinetic inductance detector (KID) readout electronics for the PRobe far-Infrared Mission for Astrophysics (PRIMA). PRIMA is a mission proposed to the 2023 NASA Astrophysics Probe Explorer (APEX) Announcement of Opportunity that will answer fundamental questions about the formation of planetary systems, as well as the formation and evolution of stars, supermassive black holes, and dust over cosmic time. The readout electronics for PRIMA must be compatible with operation at Earth-Sun L2 and capable of multiplexing more than 1000 detectors over 2 GHz bandwidth while consuming around 30 W per readout chain. The electronics must also be capable of switching between the two instruments, which have different readout bands,: the hyperspectral imager (PRIMAger, 2.5-5.0 GHz) and the spectrometer (FIRESS, 0.4-2.4 GHz). We present the driving requirements, design, and measured performance of a laboratory brassboard system.

We present the design and cryogenic characterization of highly sensitive 7 THz lens-antenna-coupled MKIDs for future actively cooled far-infrared space telescopes. This is the highest operating frequency ever demonstrated for antenna-coupled MKIDs. The detector is based on a broadband leaky-wave lens-antenna coupled to a hybrid (Al/NbTiN) CPW MKID. Both the antenna and the photosensitive Al section of the MKID lay on a thin dielectric membrane, improving both the antenna efficiency and the detector sensitivity. The high operating frequency requires the definition of sub-micron features with electron-beam lithography, pristine laser-ablated lenses, and very accurate alignments during assembly. We have tested a prototype chip and have obtained a detector noise equivalent power of 3e-20W/sqrt(Hz) with a high coupling efficiency. Additionally, we have measured the antenna beam pattern. With these measurements we demonstrate a detector system suitable for highly-sensitive (imaging) spectrometers.

We present recent progress in the development of ultra-low-noise Transition-Edge Sensors (TESs) pixels designed for far-infrared (~30-300µm) astronomical instruments. The TES sensitivity is maximized using phononic filters, which are sub-wavelength coherent filters that provide broadband rejection of thermal phonons emitted at the TES critical temperature, Tc~100mK. The phononic filter isolation legs are compact, ~50 µm. In a absorber-coupled bolometer suspended by four legs, the thermal conductance is reduced to achieve an NEP of less than 0.3 aW/rtHz, which is sufficient for balloon- and space-based imaging and low-resolution spectrometer instruments with cold optics. We discuss the phononic filter and TES design, the performance of the phononic-isolated TES pixels, and the advantage of these highly-sensitive absorber-coupled TES bolometers for astronomical instruments.

While large arrays of microwave kinetic inductance detectors (MKIDs) have been demonstrated with photon noise limited performance, imperfect frequency placement due to fabrication non-uniformity has led to resonators that collide with their frequency neighbors. Though physically yielded, the excess cross talk means that they are unusable for science applications. This would lead to reduced performance when placed on telescopes such as the CCATs FYST. However, we can use the LED trimming method developed at NIST to identify the non-uniformities, the resonator location to frequency correspondence, and then re-etch the resonators to correct them to an optimal position. This process has been demonstrated on a CCAT 280 GHz MKID array. We will show the results of the trimming of 3456 resonators on the array, and how the yield would be improved while maintaining the optical performance of the pixels. This demonstrates a path towards ideal wafer-scale MKID arrays.

Proposed for a late 2031 launch, PRIMA, the Probe far-Infrared Mission for Astrophysics, closes the gap between JWST and ALMA, offering unprecedented sensitivity and spectroscopic mapping capability in the 24-264 μm range for detailed studies of galactic evolution, planetary atmospheres, and dust-metal dynamics. Onboard PRIMA, the PRIMAger camera operates in the 25-80 μm bands utilizing advanced MKID detector modules for hyperspectral imaging enabled by Linear Variable Filters. This paper presents a graded resonant metal-mesh filter technology, demonstrating very promising efficiency in the short wavelength range. Overcoming dielectric loss limitations, an innovative dual-layer LVF design on thin membranes achieves a transmission of 80-90% at 12 THz. Rigorous electromagnetic modeling, optimization, and position-dependent spectral response measurements validate the filter performance. We present a comprehensive set of simulation and experimental results, including environmental pre-qualification tests, strongly supporting the suitability of this technology for future space applications.

Millimeter/sub-millimeter spectroscopy enables access to a vast cosmic volume through measurements of redshifted CII and CO rotation lines. This provides unprecedented opportunities to study large-scale structures and their evolution. As a recently advanced technology, the on-chip filter-bank spectrometer offers the advantage of reducing overall instrumental complexity. However, one challenge of the current design arises from the large footprint occupied by the filter bank, significantly diminishing pixel packing density on the telescope's focal plane. As the success of next-generation line intensity measurements relies on higher spectral resolution and improved array sensitivity, this presentation introduces a multi-level focal plane design aimed at substantially increasing pixel packing density. We build a prototype using feedhorn-coupled OMTs and optimize the design for typical filter bank geometries like those used for SPT-SLIM. The coupling between feedhorns and OMTs on different layers is simulated in COMSOL. We will present testing results of the prototype as a validation of the concept.

The Terahertz Intensity Mapper (TIM) is a NASA-funded balloon-borne telescope that aims to measure the [CII] emission from star forming galaxies over an enormous cosmic volume. TIM’s cryogenic receiver, based on the BLAST-TNG design, utilizes a three-stage He sorption refrigerator backed by a 280-liter liquid helium tank to achieve a base temperature of 250 mK, which enables photon noise-limited performance for its MKID detectors. Two low-impedance multi-channel heat exchangers enhance cooling efficiency, contributing to a designed hold time of 20 days under ground conditions. Preliminary simulations and assembly tests showcase the cryostat's reliability, and data validation is anticipated by the summer of 2024. We will present the design and current status of the TIM cryogenic receiver and our ongoing characterization effort toward an Antarctic flight in 2026.

Titanium nitride (TiN) is an ideal material for fabricating Kinetic Inductance Detectors (KIDs), firstly due to its relatively high and tuneable critical temperature, and secondly its high normal-state resistivity, which allows for a large kinetic inductance and responsivity. However, fabricating large arrays on wafers greater than 150 mm can be challenging due to TiN films being very sensitive to changes in stoichiometry, thickness and contaminants. In this paper we demonstrate a novel technique for making high quality films of superconducting TiN via the use of a high impulse magnetron sputtering technique (HIPIMs) in conjunction with a custom built ultra-high vacuum environment. We detail the design principles of the UHV-HIPIMS sputter system and show that films of high uniformity suitable for use in KID arrays can be achieved.

The BICEP3 and BICEP Array polarimeters are small-aperture refracting telescopes located at the South Pole designed to measure primordial gravitational wave signatures in the Cosmic Microwave Background (CMB) polarization, predicted by inflation. Constraining the inflationary signal requires not only excellent sensitivity, but also careful control of instrumental systematics. Both instruments use antenna-coupled orthogonally polarized detector pairs, and the polarized sky signal is reconstructed by taking the difference in each detector pair. As a result, the differential response between detectors within a pair becomes an important systematic effect we must control. Additionally, mapping the intensity and polarization response in regions away from the main beam can inform how sidelobe levels affect CMB measurements. Extensive calibration measurements are taken in situ every austral summer for control of instrumental systematics and instrument characterisation. In this work, we detail the set of beam calibration measurements that we conduct on the BICEP receivers, from deep measurements of main beam response to polarized beam response and sidelobe mapping. We discuss the impact of these measurements for instrumental systematics studies and design choices for future CMB receivers.

Silicon-platelet feedhorn technology is well established at millimeter wavelengths and can provide significant advantages over traditional direct-machined metal feedhorns. Past experiments have required just a few arrays, each built from ~50x lithographically processed wafers – a practical amount for a research lithographic microfabrication facility. However, scaling production to dozens of such arrays for future large-scale experiments may be unfeasible. Here we explore an alternative fabrication approach: laser-micromachining of silicon wafers – a scalable solution with potential advantages in fabrication speed, labor, and throughput.

We characterize a prototype array of laser-micromachined feedhorns designed for operation in the band 80–160 GHz. We compare the optical performance of these horns at room-temperature to horns produced using the traditional DRIE process, and contrast both against simulation. Furthermore, we explore additional potential advantages to laser-micromachining, e.g. sidewall control and thicker wafers. Finally, we share fabrication experience and discuss the outlook for high-throughput feedhorn production using laser-machined wafers.

As millimeter-wave cosmology experiments refine their optical chains, precisely characterizing their optical materials under cryogenic conditions becomes increasingly important. For instance, as the aperture sizes and bandwidths of millimeter-wave receivers increase, the design of antireflection coatings becomes progressively more constrained by an accurate measure of material optical properties in order to achieve forecasted performance. Likewise, understanding dielectric and scattering losses is relevant to photon noise modeling in presently-deploying receivers such as BICEP Array and especially to future experiments such as CMB-S4. Additionally, the design of refractive elements such as lenses necessitates an accurate measure of the refractive index. High quality factor Fabry–Pérot open resonant cavities provide an elegant means for measuring these optical properties. Employing a hemispherical resonator that is compatible with a quick-turnaround 4 Kelvin cryostat, we can measure the dielectric and scattering losses of low-loss materials at both ambient and cryogenic temperatures. We review the design, characterization, and metrological applications of quasioptical cavities commissioned for measuring the dielectric materials in the BICEP3 (95 GHz) and BICEP Array mid-frequency (150 GHz) optics. We also discuss the efforts to improve the finesse of said cavities, for better resolution of degenerate higher order modes, which can provide stronger constraints on cavity parameters and sample material thickness.