Design and Simulation of a Microwave Kinetic Inductance Detector Spectrograph for Astronomy

Abstract

This thesis presents a Microwave Kinetic Inductance Detector (MKID) spectrograph concept, the Kinetic Inductance Detector Spectrometer (KIDSpec). MKIDs are superconducting photon-counting detectors that can resolve the energy of incoming photons and their time of arrival. KIDSpec will use these detectors to separate incoming spectral orders from a
grating, thereby not requiring a cross-disperser. In Chapter 3, a simulation tool is presented for assessing KIDSpec’s potential performance upon construction to optimise a given design. This simulation tool is the KIDSpec Simulator (KSIM), a Python package designed to simulate various KIDSpec and observation parameters. A range of astrophysical objects is simulated, including stellar objects, an SDSS-observed galaxy, a Seyfert galaxy, and a mock galaxy
spectrum from the JAGUAR catalogue. Multiple medium spectral resolution designs for KIDSpec are simulated. The possible impact of MKID energy resolution variance and dead pixels is also simulated, with observed impacts on KIDSpec performance assessed using the Reduced Chi-Squared (RCS) value. Using dead pixel percentages from current instruments, the RCS result was found to increase to only 1.21 at worst for one of the designs simulated. SNR comparisons of object simulations between KSIM and X-Shooter’s ETC were
also performed. KIDSpec demonstrates a particular improvement over XShooter for short and faint observations. For a Seyfert galaxy (mR = 21) simulation with a 180s exposure, KIDSpec achieved an average SNR of 4.8,
compared to 1.5 for X-Shooter. By using KSIM, the design of KIDSpec can be optimised to further enhance the instrument.
Chapter 4 presents the Superconducting Spectrograph for Medium resolution in an Array of Telescopes (SuperSmart). This concept would utilise an array of small (≤1m diameter) telescopes, each with a KIDSpec-style instrument connected
optically with a fibre. A key benefit of this would be the use of MKIDs,which would allow these smaller telescopes to bin the photons they observe together, effectively becoming the equivalent of a larger-class telescope, such
as a 4m-class telescope. The concept and a design for the array is presented, with KSIM simulations used to predict the performance of both individual telescopes and the array as a whole. The simulations include limiting magnitudes,
a set of survey objects from GAIA, and LISA calibration sources. If enough 0.6m diameter telescopes are used to reach a total equivalent telescope
diameter of 4m, SuperSmart would need 190 nights to observe 100,000 objects of mV < 19. This assumes that each telescope can act independently and does
not require the rest of the array to finish an observation before moving to a new object. If this independence is not considered, the required nights more than doubled to 477 nights. From KSIM simulations, SuperSmart could characterise
important gravitational wave sources for LISA. To halve the standard error on the radial velocity semi-amplitude of ZTF J1539+5027, SuperSmart would utilise the time resolution and lack of read noise. This would involve
using exposures of 9s throughout the ≈ 414s period and improving the signal to noise ratio in these time bins over 15 hours of observation. An important part of MKID operation is the analysis of the data received from
the MKID. Initially, this involves characterising the MKID before analysing the data stream for photon events. Chapter 5 describes the methods used for this. Chapter 6 presents the KIDSpec Prototype. The Prototype is a
fibre-fed spectrograph, with the camera affixed on an arm articulating from the grating. The MKID, which is fibre-fed from the output of the camera, then separates the spectral orders that the camera observes. The concept,
design, and assembly are presented, along with data taken from calibration lamps and the Sun. Full spectra of the bandpass ≈ 300 − 1500nm are observed from the calibration lamps; however, a solar spectrum was not achieved due to
poor weather with intermittent clouds in Durham, UK. Nevertheless, photons were observed and separated between the orders, demonstrating the MKID’s capability for spectrographs.