Superconducting kinetic inductance detectors will play an important role in the future of exoplanet spectroscopy. Their low bandgap and the possibillity that they can be multiplexed into large arrays open up new opportunities where conventional semiconductors stop. A key requirement for the performance of these new detectors is the consistency of their quality factor (Q-factor). Variations in Q-factors, known as Q-scatter, result in nonuniform sensitivity and hold back scaling to larger systems.

In this thesis, detectors that differ in fabrication, pixel count and pixel spacing are analyzed and compared to find out what is the cause of Q-scatter. Possible causes include design errors, inaccurate fabrication, electromagnetic crosstalk, magnetic vortices and unbalanced transmission lines. Analysis showed Q-scatter is unlikely to be impacted by design, fabrication method, electromagnetic coupling or vortex forming. Also, no spatial relations, that indicated any transmission line effects, were observed. What is interesting however, is that the Q-factors of one of the chips seem to scatter all over again when measuring the chip again after trimming one of its components.

With the data available in this experiment it was not possible to give an concrete cause of Q-scatter. Furhter experiments, especially concerning the new scattering need to be conducted. Also, simulations using Sonnet v19 can give more insights in the origin of Q-scatter. ... Read more

In the mission of understanding the origins of life on earth and in the universe, astronomers are looking to exoplanets for signs of life. The spectra of light that has passed through an exoplanet's atmosphere is analysed for biomarkers. Until now most exoplanets have been found and characterised using the transit method. In the coming decade the aim is to look for planets using direct detection methods. In part for this purpose the European Extremely Large Telescope (EELT) is currently under construction and in future the Habitable World Observatory (HWO) is planned as a space-based telescope. To make full use of the EELT and the WHO extreme adaptive optics (XAO) systems using wave front sensors and deformable mirrors are needed. Contemporary CCD cameras utilizing semiconductor band gap energies are not sufficiently sensitive for wavefront sensing in direct exoplanet detection, let alone perform measurements to characterise their atmospheres. To this end different detectors are needed.

Kinetic inductance detectors (KIDs) are promising superconducting, energy resolving devices capable of single photon detection in the near-infrared and visible regimes. Another often cited advantage of KIDs is that, in theory, many detectors can easily be coupled to a single set of readout electronics. To make devices capable of producing images comparable to those achieved with CCDs we need a similar amount of pixels. The largest KID arrays to date are in the order of a thousand pixels on one readout line, whereas CCDs have in the order of millions of pixels. In this thesis some theoretical and practical limits on KID multiplexability while retaining high pixel yield are explored. ... Read more

Extremely large telescopes (ELTs) are expected to be one of the most promising astronomical observation instruments when it comes to observing exoplanets. During observations, however, Earth’s atmosphere introduces optical distortion, which needs to be corrected. For this reason, a wavefront sensor (WFS) will be developed that comprises a 100 ⇥ 100 array of kinetic inductance detectors (KID), superconductor-based photodetectors. The main advantage of KIDs in an array is their ability to be multiplexed on a single read out line by designing each KID to operate at a different frequency. The signal of an individual KID can essentially be described as a dip in the transmission signal of the readout signal. Upon the fabrication of these KID arrays, however, these dips may have shifted as so-called frequency scatter (or f-scatter), which severely disorders the readout signal. The f-scatter cannot be determined based solely on the readout signal as it contains no information about which KID each individual signal originates from.
This paper manages to provide a solution in the form of an experimental method in which the KID array is scanned along the x- and y-axis to produce a spatial map. To realize this, an optical setup was designed and constructed, based on a single-lens system with a magnification of M = 1.22. By implementing a CCD camera, the KID array could be live imaged to align the setup accordingly. Thanks to numerous other alignment measures, the setup was able to scan the entire KID array along the x- and y-axis in 45 scans per axis. Based on the difference in transmission, a 45x45 spatial map was constructed, which was manually scaled down to 20x20. This 20x20 spatial map presented the location of KIDs on the fabricated detector array based on their measured operating frequency. By comparing this with the spatial map of the KID array design, the standard deviation in the fractional frequency deviation was determined, σ_δf/f = 5.92 · 10^-3. This result shows the experimental method is able to effectively unveil the severity of the f-scatter in the studied 20x20 KID array.
Despite the potency of the presented method, the biggest giveaway of its flaws is a reduced pixel yield on the 20x20 spatial map from 400 to 374 pixels. The developed data analysis is able recognize multiple complications, which can be mitigated by optimizing readout parameters to improve the quality of the signal. Additionally, one-to-one imaging is far too restricting for advanced scanning techniques due to its fixed M. Appropriate suggestions for improving the lens systems would be implementing the Cooke triplet or a two-lens system that utilizes the principle of virtual imaging. ... Read more