Development Of Kinetic Inductance Detectors For Far-Infrared Spectroscopy In Astrophysics

This thesis presents the development of kinetic inductance detectors targeted for applications in far-infrared spectroscopy in astrophysics. The formation and evolution of galaxies across cosmic time is one of the key areas of exploration in modern astrophysics. The star formation rate density peaks at a redshift of around z=2, when the universe was dominated by dusty star-forming galaxies whose optical and ultraviolet radiation are significantly obscured and thermally reprocessed by dust into infrared radiation. A swath of fine-structure lines in the far-infrared serve as tracers of star formation activity in these galaxies, and far-infrared continuum and line emission are unobscured by dust. However, detecting these lines in individual galaxies is difficult and time consuming with currently-available infrared instruments. The Terahertz Intensity Mapper (TIM) experiment is a balloon-borne telescope spectrometer that will observe these galaxies leading back to the era of peak star formation. TIM will use the intensity mapping technique to create a three-dimensional map, incorporating the spectral dimension as the line-of-sight coordinate. This measurement will survey the aggregate star-formation activity as a function of redshift of the total galaxy population without a flux limit. TIM will incorporate two grating spectrometer modules to observe the 240-420 micron wavelength band with spectral resolution R = 250, each with 1800 low-noise kinetic inductance detectors (KIDs) in its focal plane. I present the development and testing of prototype KID arrays targeted for use on TIM. KIDs are superconducting microresonators that serve as radiation detectors. They rely on the kinetic inductance effect, which causes a shift in resonant behavior when incident photons are absorbed by Cooper pairs in the superconductor material. I present characterization results from two 45-pixel KID arrays fabricated out of thin-film aluminum on silicon substrates. I demonstrate that their device performance meets the sensitivity and noise requirements for the TIM experiment

Optimization of an Optical Testbed for Characterization of EXCLAIM u-Spec Integrated Spectrometers

We describe a testbed to characterize the optical response of compact superconducting on-chip spectrometers in development for the Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) mission. EXCLAIM is a balloonborne far-infrared experiment to probe the CO and CII emission lines in galaxies from redshift 3.5 to the present. The spectrometer, called u-Spec, comprises a diffraction grating on a silicon chip coupled to kinetic inductance detectors (KIDs) read out via a single microwave feedline. We use a prototype spectrometer for EXCLAIM to demonstrate our ability to characterize the spectrometers spectral response using a photomixer source. We utilize an on-chip reference detector to normalize relative to spectral structure from the off-chip optics and a silicon etalon to calibrate the absolute frequency

Developing a New Generation of Integrated Micro-Spec Far Infrared Spectrometers for the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM)

The current state of far-infrared astronomy drives the need to develop compact, sensitive spectrometers for future space and ground-based instruments. Here we present details of the $\rm \mu$-Spec spectrometers currently in development for the far-infrared balloon mission EXCLAIM. The spectrometers are designed to cover the $\rm 555 - 714\ \mu$m range with a resolution of $\rm R\ =\ \lambda / \Delta\lambda\ =\ 512$at the$\rm 638\ \mu$m band center. The spectrometer design incorporates a Rowland grating spectrometer implemented in a parallel plate waveguide on a low-loss single-crystal Si chip, employing Nb microstrip planar transmission lines and thin-film Al kinetic inductance detectors (KIDs). The EXCLAIM$\rm \mu$-Spec design is an advancement upon a successful$\rm R = 64\ \mu$-Spec prototype, and can be considered a sub-mm superconducting photonic integrated circuit (PIC) that combines spectral dispersion and detection. The design operates in a single$M{=}2$grating order, allowing one spectrometer to cover the full EXCLAIM band without requiring a multi-order focal plane. The EXCLAIM instrument will fly six spectrometers, which are fabricated on a single 150 mm diameter Si wafer. Fabrication involves a flip-wafer-bonding process with patterning of the superconducting layers on both sides of the Si dielectric. The spectrometers are designed to operate at 100 mK, and will include 355 Al KID detectors targeting a goal of NEP${\sim}8\times10^{-19}$$\rm W/\sqrt{Hz}$. We summarize the design, fabrication, and ongoing development of these$\rm \mu$-Spec spectrometers for EXCLAIM.Comment: 9 pages, 5 figures, to appear in the Proceedings of the SPIE Astronomical Telescopes + Instrumentation (2022

Overview and status of EXCLAIM, the experiment for cryogenic large-aperture intensity mapping

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne far-infrared telescope that will survey star formation history over cosmological time scales to improve our understanding of why the star formation rate declined at redshift z < 2, despite continued clustering of dark matter. Specifically,EXCLAIM will map the emission of redshifted carbon monoxide and singly-ionized carbon lines in windows over a redshift range 0 < z < 3.5, following an innovative approach known as intensity mapping. Intensity mapping measures the statistics of brightness fluctuations of cumulative line emissions instead of detecting individual galaxies, thus enabling a blind, complete census of the emitting gas. To detect this emission unambiguously, EXCLAIM will cross-correlate with a spectroscopic galaxy catalog. The EXCLAIM mission uses a cryogenic design to cool the telescope optics to approximately 1.7 K. The telescope features a 90-cm primary mirror to probe spatial scales on the sky from the linear regime up to shot noise-dominated scales. The telescope optical elements couple to six {\mu}-Spec spectrometer modules, operating over a 420-540 GHz frequency band with a spectral resolution of 512 and featuring microwave kinetic inductance detectors. A Radio Frequency System-on-Chip (RFSoC) reads out the detectors in the baseline design. The cryogenic telescope and the sensitive detectors allow EXCLAIM to reach high sensitivity in spectral windows of low emission in the upper atmosphere. Here, an overview of the mission design and development status since the start of the EXCLAIM project in early 2019 is presented.Comment: SPIE Astronomical Telescopes + Instrumentation. arXiv admin note: substantial text overlap with arXiv:1912.0711

Experiment for cryogenic large-aperture intensity mapping: instrument design

The experiment for cryogenic large-aperture intensity mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation in windows from the present to z  =  3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission of singly ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering 420 to 540 GHz with spectral resolving power R  =  512 and angular resolution ≈4  arc min. The spectral resolving power and cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere. EXCLAIM will survey 305  deg2 in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as tracers of molecular gas. We summarize the design phase of the mission

Development of Kinetic Inductance Detectors for Far-infrared Spectroscopy in Astrophysics

This thesis presents the development of kinetic inductance detectors targeted for applications in far-infrared spectroscopy in astrophysics. The formation and evolution of galaxies across cosmic time is one of the key areas of exploration in modern astrophysics. The star formation rate density peaks at a redshift of around z=2, when the universe was dominated by dusty star-forming galaxies whose optical and ultraviolet radiation are significantly obscured and thermally reprocessed by dust into infrared radiation. A swath of fine-structure lines in the far-infrared serve as tracers of star formation activity in these galaxies, and far-infrared continuum and line emission are unobscured by dust. However, detecting these lines in individual galaxies is difficult and time consuming with currently-available infrared instruments. The Terahertz Intensity Mapper (TIM) experiment is a balloon-borne telescope spectrometer that will observe these galaxies leading back to the era of peak star formation. TIM will use the intensity mapping technique to create a three-dimensional map, incorporating the spectral dimension as the line-of-sight coordinate. This measurement will survey the aggregate star-formation activity as a function of redshift of the total galaxy population without a flux limit. TIM will incorporate two grating spectrometer modules to observe the 240-420 micron wavelength band with spectral resolution R = 250, each with 1800 low-noise kinetic inductance detectors (KIDs) in its focal plane. I present the development and testing of prototype KID arrays targeted for use on TIM. KIDs are superconducting microresonators that serve as radiation detectors. They rely on the kinetic inductance effect, which causes a shift in resonant behavior when incident photons are absorbed by Cooper pairs in the superconductor material. I present characterization results from two 45-pixel KID arrays fabricated out of thin-film aluminum on silicon substrates. I demonstrate that their device performance meets the sensitivity and noise requirements for the TIM experiment

Development of Kinetic Inductance Detectors for Far-infrared Spectroscopy in Astrophysics

This thesis presents the development of kinetic inductance detectors targeted for applications in far-infrared spectroscopy in astrophysics. The formation and evolution of galaxies across cosmic time is one of the key areas of exploration in modern astrophysics. The star formation rate density peaks at a redshift of around z=2, when the universe was dominated by dusty star-forming galaxies whose optical and ultraviolet radiation are significantly obscured and thermally reprocessed by dust into infrared radiation. A swath of fine-structure lines in the far-infrared serve as tracers of star formation activity in these galaxies, and far-infrared continuum and line emission are unobscured by dust. However, detecting these lines in individual galaxies is difficult and time consuming with currently-available infrared instruments. The Terahertz Intensity Mapper (TIM) experiment is a balloon-borne telescope spectrometer that will observe these galaxies leading back to the era of peak star formation. TIM will use the intensity mapping technique to create a three-dimensional map, incorporating the spectral dimension as the line-of-sight coordinate. This measurement will survey the aggregate star-formation activity as a function of redshift of the total galaxy population without a flux limit. TIM will incorporate two grating spectrometer modules to observe the 240-420 micron wavelength band with spectral resolution R = 250, each with 1800 low-noise kinetic inductance detectors (KIDs) in its focal plane. I present the development and testing of prototype KID arrays targeted for use on TIM. KIDs are superconducting microresonators that serve as radiation detectors. They rely on the kinetic inductance effect, which causes a shift in resonant behavior when incident photons are absorbed by Cooper pairs in the superconductor material. I present characterization results from two 45-pixel KID arrays fabricated out of thin-film aluminum on silicon substrates. I demonstrate that their device performance meets the sensitivity and noise requirements for the TIM experiment

Second language research:Methodology and Design

We are developing lumped-element kinetic inductance detectors (LEKIDs) designed to achieve background-limited sensitivity for far-infrared (FIR) spectroscopy on a stratospheric balloon. The Spectroscopic Terahertz Airborne Receiver for Far-InfraRed Exploration (STARFIRE) will study the evolution of dusty galaxies with observations of the [CII] 158 micron and other atomic fine-structure transitions at z = 0.5 - 1.5, both through direct observations of individual luminous infrared galaxies, and in blind surveys using the technique of line intensity mapping. The spectrometer requires large format arrays of dual-polarization-sensitive detectors with NEPs of 1e-17 W/sqrt(Hz). We pattern the LEKIDs in 20-nm aluminum film, and use an array of profiled feedhorns to couple optical radiation onto the meandered inductors. A backshort etched from the backside to a buried oxide layer insures high absorption efficiency without additional matching layers. Initial testing on small sub-arrays has demonstrated a high device yield and median NEP of 4e-18 W/sqrt(Hz). We describe the development and characterization of kilo-pixel arrays using a combination of dark noise measurements and optical response with our cryogenic blackbody

Fabrication and characterization of optical filters from polymeric aerogels loaded with diamond scattering particles

We have developed a suite of infrared-blocking filters made by embedding diamond scattering particles in a polyimide aerogel substrate. We demonstrate the ability to tune the spectral performance of the filters based on both the composition of the base aerogel material and the properties of the scattering particles. We summarize the fabrication, optical modeling, and characterization of these filters. We investigate two polyimide base aerogel formulations and the effects of loading them with diamond scattering particles of varying sizes and relative densities. We describe a model for the filters' behavior using a combination of Maxwell Garnett and Mie scattering techniques. We present optical characterization results for diamond-loaded aerogel filters with cutoff frequencies (50% transmittance) ranging between 2.5 and 15 THz, and confirm that the measured spectral performance is in agreement with our optical models. We also measure the filters' refractive indices in the microwave and report findings in agreement with Maxwell Garnett model predictions (typically n < 1.08)

Optical characterization and testbed development for μ-Spec integrated spectrometers

This paper describes a cryogenic optical testbed developed to characterize µ-Spec spectrometers in a dedicated dilution refrigerator (DR) system. μ-Spec is a far-infrared integrated spectrometer that is an analog to a Rowland-type grating spectrometer. It employs a single-crystal silicon substrate with niobium microstrip lines and aluminum kinetic inductance detectors (KIDs). Current designs with a resolution of R = λ/Δλ = 512 are in fabrication for the EXCLAIM (Experiment for Cryogenic Large Aperture Intensity Mapping) balloon mission. The primary spectrometer performance and design parameters are efficiency, NEP, inter-channel isolation, spectral resolution, and frequency response for each channel. Here we present the development and design of an optical characterization facility and preliminary validation of that facility with earlier prototype R=64 devices. We have conducted and describe initial optical measurements of R = 64 devices using a swept photomixer line source. We also discuss the test plan for optical characterization of the EXCLAIM R = 512 μ-Spec devices in this new testbed