Development of Microwave Kinetic Inductance Detectors for Applications in Optical to Near-IR Astronomy

Microwave Kinetic Inductance Detectors (MKIDs) are a superconducting detector technology capable of measuring photon arrival times to the microsecond level with moderate energy resolution. MKIDs are essentially superconducting microresonators, and when a photon is incident on the inductor portion of the microresonator, the inductance temporarily increases and the resonant frequency decreases. An array of MKIDs can be naturally multiplexed and read out by assigning each detector a unique resonant frequency during fabrication and coupling the detectors to a single transmission line. A frequency domain multiplexing scheme can then be used to pass a microwave frequency comb through the transmission line to probe the microresonators and listen for photon events. In order to meet the demands of the next generation of astronomical instrumentation, MKIDs need improvements in three main areas: pixel yield, energy resolution, and quantum efficiency. I have investigated new fabrication techniques and materials systems to address these issues. Most notably, I have fabricated MKIDs with platinum silicide as the superconducting layer and have measured especially high resonator internal quality factors (>10^6). Platinum silicide films can also be made much more uniformly than the traditional sub-stoichiometric titanium nitride films used in the field, increasing pixel yield. In addition, platinum silicide intrinsically has a higher absorption rate for optical photons than titanium nitride. These platinum silicide detectors are used in two new MKID planet imaging instruments, the Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer (DARKNESS) and the MKID Exoplanet Camera (MEC). Optical MKIDs have already been demonstrated on sky with the first generation MKID instrument, the Array Camera for Optical to Near-IR Spectrophotometry (ARCONS). I have used ARCONS to primarily observe compact objects, such as AM CVn systems and detached white dwarfs. In particular, I used ARCONS to observe orbital expansion in the eclipsing binary system SDSS J0926+3624, with a period rate of change of 9.68 microseconds/year.I open my thesis with an general introduction to the field of low temperature detectors and describe the role that MKIDs have within the field. In Chapter 2, I provide a detailed description of the detection principles behind MKIDs and define important superconducting resonator parameters.In Chapter 3, I move on to describe some of the issues that were limiting the performance of MKIDs. I examine some of the early fabrication techniques and material systems utilized to try to mitigate these issues. In Chapter 4, I describe the platinum silicide material system, which proved to be the most important recent development for advancing the detectors described in this work. The early PtSi work was done using simple one-layer test masks, but the material system was later adapted to the full-multilayer fabrication process. The fabrication of large-format MKID arrays using PtSi for the DARKNESS and MEC arrays is described in detail in Chapter 5.I conclude my thesis with an overview of some of the astronomical applications of MKIDs. More specifically, I describe my work with compact binary systems that was done with ARCONS. Finally, I explain exciting new MKID applications that are only recently becoming possible as the technology continues to advance

The MKID Exoplanet Camera for Subaru SCExAO

We present the MKID Exoplanet Camera (MEC), a z through J band (800 - 1400 nm) integral field spectrograph located behind The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) at the Subaru Telescope on Maunakea that utilizes Microwave Kinetic Inductance Detectors (MKIDs) as the enabling technology for high contrast imaging. MEC is the first permanently deployed near-infrared MKID instrument and is designed to operate both as an IFU, and as a focal plane wavefront sensor in a multi-kHz feedback loop with SCExAO. The read noise free, fast time domain information attainable by MKIDs allows for the direct probing of fast speckle fluctuations that currently limit the performance of most high contrast imaging systems on the ground and will help MEC achieve its ultimate goal of reaching contrasts of $10^{-7}$ at 2$\lambda / D$. Here we outline the instrument details of MEC including the hardware, firmware, and data reduction and analysis pipeline. We then discuss MEC's current on-sky performance and end with future upgrades and plans.Comment: To be published in Publications of the Astronomical Society of the Pacifi

MKID Exoplanet Camera for Subaru SCExAO

We present the MKID Exoplanet Camera (MEC), a z through J band (800–1400 nm) integral field spectrograph located behind The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) at the Subaru Telescope on Maunakea that utilizes Microwave Kinetic Inductance Detectors (MKIDs) as the enabling technology for high contrast imaging. MEC is the first permanently deployed near-infrared MKID instrument and is designed to operate both as an IFU, and as a focal plane wavefront sensor in a multi-kHz feedback loop with SCExAO. The read noise free, fast time domain information attainable by MKIDs allows for the direct probing of fast speckle fluctuations that currently limit the performance of most high contrast imaging systems on the ground and will help MEC achieve its ultimate goal of reaching contrasts of 10⁻⁷ at 2 λ/D. Here we outline the instrument details of MEC including the hardware, firmware, and data reduction and analysis pipeline. We then discuss MEC's current on-sky performance and end with future upgrades and plans

DARKNESS: A Microwave Kinetic Inductance Detector Integral Field Spectrograph for High-Contrast Astronomy

We present DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer), the first of several planned integral field spectrographs to use optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs will enable real-time speckle control techniques and post-processing speckle suppression at framerates capable of resolving the atmospheric speckles that currently limit high-contrast imaging from the ground. DARKNESS is now operational behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory. Here we describe the motivation, design, and characterization of the instrument, early on-sky results, and future prospects.Comment: 17 pages, 17 figures. PASP Publishe

A tabletop x-ray tomography instrument for nanometer-scale imaging: demonstration of the 1,000-element transition-edge sensor subarray

We report on the 1,000-element transition-edge sensor (TES) x-ray spectrometer implementation of the TOMographic Circuit Analysis Tool (TOMCAT). TOMCAT combines a high spatial resolution scanning electron microscope (SEM) with a highly efficient and pixelated TES spectrometer to reconstruct three-dimensional maps of nanoscale integrated circuits (ICs). A 240-pixel prototype spectrometer was recently used to reconstruct ICs at the 130 nm technology node, but to increase imaging speed to more practical levels, the detector efficiency needs to be improved. For this reason, we are building a spectrometer that will eventually contain 3,000 TES microcalorimeters read out with microwave superconducting quantum interference device (SQUID) multiplexing, and we currently have commissioned a 1,000 TES subarray. This still represents a significant improvement from the 240-pixel system and allows us to begin characterizing the full spectrometer performance. Of the 992 maximimum available readout channels, we have yielded 818 devices, representing the largest number of TES x-ray microcalorimeters simultaneously read out to date. These microcalorimeters have been optimized for pulse speed rather than purely energy resolution, and we measure a FWHM energy resolution of 14 eV at the 8.0 keV Cu K$\alpha$ line.Comment: 5 pages, 4 figures, submitted to IEEE Transactions on Applied Superconductivit

A Tabletop X-Ray Tomography Instrument for Nanometer-Scale Imaging: Integration of a Scanning Electron Microscope with a Transition-Edge Sensor Spectrometer

X-ray nanotomography is a powerful tool for the characterization of nanoscale materials and structures, but is difficult to implement due to competing requirements on X-ray flux and spot size. Due to this constraint, state-of-the-art nanotomography is predominantly performed at large synchrotron facilities. Compact X-ray nanotomography tools operated in standard analysis laboratories exist, but are limited by X-ray optics and destructive sample preparation techniques. We present a laboratory-scale nanotomography instrument that achieves nanoscale spatial resolution while changing the limitations of conventional tomography tools. The instrument combines the electron beam of a scanning electron microscope (SEM) with the precise, broadband X-ray detection of a superconducting transition-edge sensor (TES) microcalorimeter. The electron beam generates a highly focused X-ray spot in a metal target, while the TES spectrometer isolates target photons with high signal-to-noise. This combination of a focused X-ray spot, energy-resolved X-ray detection, and unique system geometry enable nanoscale, element-specific X-ray imaging in a compact footprint. The proof-of-concept for this approach to X-ray nanotomography is demonstrated by imaging 160 nm features in three dimensions in a Cu-SiO2 integrated circuit, and a path towards finer resolution and enhanced imaging capabilities is discussed.Comment: The following article has been submitted to Physical Review Applie