The single-pixel integrated superconducting spectrometer DESHIMA 2.0 on 10 m Atacama Submillimeter Telescope Experiment (ASTE) aims to provide broadband spectra from 200 to 400 GHz at medium resolution. This spectral range enables observations of (sub) millimetre-wave astronomy, especially for uncovering dust-obscured cosmic star formation and galaxy evolution over cosmic time. To test its scientific capabilities, the nearby star-forming and AGN galaxy NGC 1068 was observed. This study compares the observed DESHIMA 2.0 spectrum against published literature on NGC 1068, addressing the research question: Is the wideband spectrum of NGC 1068 obtained with DESHIMA 2.0 consistent with pre- viously published observational data?
The dust continuum was extracted by fitting a grey-body with a statistical model using a Markov Chain Monte Carlo (MCMC) sampler over the 250-280 GHz window. The best-fit parameters were found to agree with values obtained by Z-spec at the 1𝜎 level, with a reduced 𝜒2 = 1.37 achieved with the data and 𝜒2 = 3.32 with continuum model over Z-spec observed data, showing good continuum recovery. Voigt profiles were fitted to the CO(2-1) and CO(3-2) lines using single fits on continuum-subtracted spectra. The emission line fluxes comparable to those obtained with the James Clerk Maxwell Telescope (JCMT) by Qiu et al. were measured by DESHIMA 2.0, agreeing within 6–12%. However, significant differences were observed in line widths and main beam temperatures, attributed to instrumental effects such as beam dilution and smearing, as well as methodological differences between single Voigt profile and multi-component Gaussian fitting approaches.
It is demonstrated that DESHIMA 2.0 delivers reliable broadband continuum and integrated emission line fluxes consistent with other instruments for NGC 1068, validating its utility for spectral surveys of bright dusty star-forming galaxies. The observed differences in line widths and channel-to-channel calibration highlight opportunities for improved MKID correspondence and noise reduction to enable the detection of fainter emission lines in future observations.

Deposited dielectrics with low loss at millimeter-submillimeter (mm-submm) wavelengths are beneficial for the development of superconducting integrated circuits (ICs) for astronomy, such as filter banks, on-chip Fourier-transform spectrometers, and kinetic inductance parametric amplifiers. Although it is possible to fabricate microstrip lines using crystalline Si extracted from a silicon-on-insulator wafer by a flip-bonding process, deposited dielectrics al- low for simpler and more flexible chip designs and fabrication routes. In the ∼10–100 THz frequency range, dielectric losses are typically dominated by infrared absorption due to vibrational modes, whereas in the microwave fre- quency band (∼1–10 GHz) and at sub-Kelvin temperatures the dielectric loss is typically dominated by absorption due to two-level systems (TLSs). How- ever, the origin of the mm-submm (∼0.1–1 THz) loss in deposited dielectrics was unknown. In this dissertation we show that the mm-submm loss in de- posited dielectrics can be explained by the absorption tail of vibrational modes which are located above 10 THz. Furthermore, we found that hydrogenated amorphous silicon carbide (a-SiC:H) has a very low mm-submm loss tangent of 1.3×10−4 at 350 GHz, which makes it a promising low-loss deposited dielectric for mm-submm superconducting integrated circuits.

Based on a literature study we identified a-SiC:H and hydrogenated amor- phous silicon (a-Si:H) as potentially promising low-loss dielectrics. In order to find the origin of the mm-submm loss, and to define which materials we investi- gated in this PhD project, we characterized the dielectrics’ material properties at room temperature prior to performing the cryogenic loss measurements. We deposited a-SiC:H at a substrate temperature Tsub of 400◦C using plasma- enhanced chemical vapor deposition (PECVD), and we deposited the a-Si:H films at Tsub of 100◦C, 250◦C, and 350◦C. We characterized the films’ material properties using Fourier-transform infrared spectroscopy (FTIR), Raman spec- troscopy and ellipsometry. For the a-Si:H we determined the hydrogen content and the microstructure parameter from the FTIR data, the bond-angle disorder from the Raman data, and the void volume fraction from the ellipsometry data. For both the a-Si:H and the a-SiC:H we determined the band gap and optical refractive index from the ellipsometry data, and the infrared refractive index from the FTIR data. From the Raman spectra we observed that the a-SiC:H and the a-Si:H films were amorphous. Furthermore, we performed electron diffraction spectroscopy to determine the Si to C ratio of the a-SiC:H. For the a-Si:H we found that the all the material properties depend monotonically on Tsub. Additionally, we measured the cryogenic microwave loss of the a-Si:H films, but we found no correlation between the microwave loss and Tsub.

No cryogenic mm-submm and microwave loss data was available for a- SiC:H. We measured the low-power and cryogenic microwave loss of the a- SiC:H and found that the microwave loss tangent (tanδ ∼ 10−5) is compa- rable to the loss of a-Si:H. Furthermore, we measured the mm-submm loss in the range of 270–385 GHz using an on-chip Fabry-Pérot experiment. The observed mm-submm losss value of 1.2 × 10−4 at 350 GHz was significantly lower than what was reported for a-Si:H, which previously exhibited the low- est reported microwave and mm-subm wave loss values among the deposited dielectrics which are commonly used in superconducting ICs. Furthermore, we found that the mm-submm loss of the a-SiC:H increases monotonically with frequency. This was surprising in the framework of TLSs and led us to the hypothesis that another loss mechanism than TLSs might be dominant at mm- submm wavelengths. In addition to the low losses, the a-SiC:H was found to be beneficial thanks to its very low stress, lack of blisters, and the possibility to fabricate a membrane from the a-SiC:H on a c-Si wafer.

To study the origin of the frequency dependent mm-submm loss in the a- SiC:H, we extended the on-chip Fabry-Pérot experiment to the 270–600 GHz range by making use of a wideband leaky antenna. Additionally, we measured the complex dielectric constant of the a-SiC:H in the 3–100 THz range using Fourier-transform spectroscopy (FTS). We modeled the FTS data using the Maxwell-Helmholtz-Drude (MHD) dispersion model and obtained the complex dielectric constant in the 3-100 THz range. Finally, we modeled the combined on-chip loss data from the Fabry-Pérot experiments and the FTS data by fitting the MHD dispersion model in the frequency range of 0.27–100 THz. Our model demonstrates that the mm-submm loss in the a-SiC:H above 200 GHz can be explained by the absorption tail of vibrational modes which are located above 10 THz. These results pave the way for a thorough understanding of the mm-submm loss in deposited dielectrics.

The low losses of the a-SiC:H allow for integrated superconducting spec- trometers with a large frequency bandwidth and relatively high resolving pow- ers without sacrificing too much optical efficiency. This has led to the application of the a-SiC:H in the DESHIMA 2.0 filter bank, which has seen first light in 2023 at the ASTE telescope in the Atacama Desert.

Galaxy clusters are some of the largest known structures in the universe. Studying them observationally and theoretically can provide a lot of information on how these clusters form and are structured. One way to study them is through the so-called Sunyaev-Zel’dovich (SZ) effect, which is an interaction between the cosmic microwave background (CMB) and hot electrons in the cluster medium. The SZ effect can be further broken down into a thermal component (tSZ) arising from the random motion of the electrons, and a kinematic component (kSZ) arising from the bulk motion of the cluster medium, making it a good probe for several properties of the cluster. The SZ effect can be observed as a distortion of the CMB spectrum using submillimeter spectrometry. However, at many submillimeter frequencies radiation is absorbed strongly by the atmosphere. This makes it hard to interpret the measured SZ signal, and measurements require long observation times in order to reach a sufficient signal-to-noise ratio. In this thesis, we present a framework that simulates a submillimeter spectrometer observation of the tSZ effect including noise factors. It then fits a model tSZ signal to the noisy signal. This allows us to investigate the relation between observation time, noise and retrievability of cluster properties. We simulate a galaxy cluster with an electron temperature 𝑇𝑒 = 15.3 keV and central optical depth 𝜏𝑒 = 0.0172 with two simulated DESHIMA-type filterbanks spanning different frequency ranges. For each filterbank we perform 20 simulations with an observation time of 16 hours each, and 20 simulations of 32 hours. We fit every simulation separately, but average over simulations to obtain an expectation value for 𝑇𝑒 and 𝜏𝑒 given a filterbank and observation time. We also repeat each fit over rebinned copies of the noisy spectra, combining 7 data points into each bin. All tested combinations of filterbanks and observation times produce fits with results that are consistent with the input parameters. The 160-320 GHz filterbank consistently gives lower errors than the 220-440 GHz filterbank. From rebinning, we do not find any significant improvement or degradation of the quality of the fits. The estimates obtained from rebinned data deviate very little from the original estimates, by at most 5%, and show no change in consistency. From this result, we conclude that SZ observations using DESHIMA 2.0 could provide estimates on cluster parameters. These estimates are already consistent after 16 or 32 hours of observation time. However, we recommend a new filterbank design that covers 160-320 GHz since the error on estimates using this range are smaller than the errors obtained using the original 220-440 GHz filterbank. This is likely due to the atmosphere absorbing much less radiation at this frequency range. Additionally, the results from rebinning show that this new filterbank could contain fewer filters with a lower resolving power without degradation of fit quality.

The DESHIMA 2.0 spectrometer, installed on the ASTE telescope, is designed to enable broadband, high-sensitivity observations in the submillimetre wavelength range. This design allows simultaneous observation across a wide frequency range, making it possible to detect multiple emission lines in a single measurement. This is particularly useful for identifying emission lines from distant galaxies with unknown redshifts, allowing redshift determination in a single observation. This study evaluates the sensitivity and noise limitations of DESHIMA 2.0, addressing whether its on-sky performance aligns with a photon-noise model and lab-measured instrument characteristics.

First, the sensitivity of DESHIMA 2.0, integrated with the ASTE telescope, is assessed under fixed tele- scope conditions by observing the atmospheric signal without nodding the telescope or beam-switching. Observations confirm that the instrument operates near the photon-noise limit, consistent with theoret- ical predictions and laboratory measurements.

Next, a combined ABBA chopping-and-nodding technique, which integrates beam-switching with nod- ding of the telescope, is implemented to mitigate atmospheric noise during observations. This study demonstrates that this approach effectively filters out atmospheric noise over integration times of up to 3000 seconds, achieving a standard deviation of the noise level on the order of 10−4 K in the 250 to 300 GHz range. These findings confirm that the instrument maintains photon-noise-limited perfor- mance under varying atmospheric conditions.

Finally, the observed spectrum of Mars is compared to its known spectral characteristics to validate the sensitivity and calibration of DESHIMA 2.0 for bright astronomical sources. Although the observed spectrum closely resembles the known spectrum of Mars, the remaining channel-to-channel deviations exceed what the photon-noise model predicts. This highlights the presence of systematic calibration er- rors and deviations in noise behaviour. These results underscore the need for further refinement of the calibration process and the ABBA chopping analysis to enhance performance for fainter astronomical sources.

Overall, this study establishes that DESHIMA 2.0 achieves photon-noise-limited performance under specific observational setups, marking an important milestone for high-sensitivity submillimetre astron- omy. However, further work is needed to optimize the system for detecting weaker signals from distant sources, such as dusty star-forming galaxies, where signal strengths are much weaker.

To better understand the formation of stars in dusty star-forming galaxies (DSFGs), and the evolution of this type of submillimeter galaxies (SMGs), it is of high significance to perform submillimeter/far-infrared surveys. The Deep Spectroscopic High-redshift Mapper 2.0 (DESHIMA2.0) on the ASTE telescope in Chile has been designed to observe the redshifted emission lines of these DSFGs to measure both their (spectroscopic) redshifts and molecular compositions. DESHIMA2.0 is designed to observe across the 220-440 GHz frequency band using its 347 channel integrated superconducting spectrometer (ISS) chip.

The current DESHIMA2.0 instrument has been tested in the lab. Its 332 filter channels with center frequencies in the range of 204-391 GHz have a spectral resolution of f/δf ≈ 340. Their coupling efficiencies can be approximated by Lorentzian functions.

The gravitationally lensed ultraluminous high-redshift DSFG J1329+2243 with redshift z = 2.04 shows emission lines of molecular gases like CO and H2O in the frequency band of DESHIMA2.0. Using the Time-dependent End-to-end Model for Post-process Optimization (TiEMPO), an 8-hour observation of the J1329+2243 galaxy has been simulated for both the lab-measured chip and the designed chip. Two measures of sensitivity, the noise equivalent flux density (NEFD) and the minimum detectable line flux (MDLF), are theoretically derived and subsequently used to be compared with the results of the simulations. The results yielded from these simulations are ultimately used to report on the overall performance of the lab-measured chip.

To run a TiEMPO simulation using the lab-measured chip, adaptations had to be made to the model for it to accept customizable chip data. Within TiEMPO, variable spectral resolutions and coupling efficiencies had to be introduced as well as a crucial addition to enable the creation of a new filterbank. Given the results of the simulations, it can be stated that this implementation of the lab-measured chip has been successful.

After applying an ON-OFF (dual) sky chopping technique to the simulated observation to cancel fluctuations of the atmospheric transmission, the atmosphere-corrected antenna temperature of the J1329+ 2243 galaxy could be found. The standard deviation of the noise showed to be scaling inversely proportional to the square root of the integration time. For five separate emission lines of the galaxy within the range of 200-310 GHz, a signal-to-noise ratio (SNR) analysis was performed and compared to the estimated theoretical proportionality to the square root of the integration time. For lines that show overlap in the spectrum, the detection was proven to be more difficult. Optimizations in the strategy used to define these signal-to-noise ratios would improve this finding.

The performance of the current DESHIMA2.0 instrument is sufficient to detect (SNR≥5) the bright CO(7-6) line of an ultraluminous high-redshift galaxy like J1329+2243 after 5.5 minutes of observation time. After 50 minutes of observation time, it is also capable of identifying the CO(6-5), the H2O(211-202), the [CI](2-1), and the CO(8-7) emission line.

When looking up to the sky and trying to detect the photons of far away stars that are still in formation, we can get access to knowledge we never had before. In order to do this, we must make sure we truly understand the nature of how photons behave in accordance to each other and to our detectors.In quantum optics we can see that these photons have a very dubious character. They are both particle and wave and neither. This makes studying how they are distributed over the spectrum of the submillimeter and millimeter wave astronomy a very big challenge. We know that this very particlewave duality is what makes up the noise that is fundamental to photons. This duality also makes them obey the BoseEinstein statistics. Hence due to their particlelike behavior, we have a noise component that resembles that of a Poisson distribution. Very much like raindrops falling down from the sky. On the other hand we have the wave nature of the photons, this causes them to arrive in bunches rather than these random raindrops. It is observed that photons arriving at a detector are corrrelated.
In this thesis we will be investigating how to incorporate the noise of the bunching of the photons into the model of TiEMPO. This model simulates the signal processing of a measurement done by the wideband spectrometer named DESHIMA. Due to the fact that DESHIMA operates in a wideband frequency range, we do theoretical research that explains the fundamental theory behind calculating the photon noise over this wideband range. We show that taking the wideband integral of the photon noise is mathematically equivalent of summing the narrowband approximation for infinitely many subbands and adding them up top each other. This approach is the previous method of calculating the photon noise over the wideband. Due to this method being valid, the question of how these variances over these smaller subbands can be additive?
Since we are dealing with the detection of photons which as previously stated is a correlated signal. By modeling a simplified version of wideband photon detection, we have come to the conclusion that due to the small coherence time these photons are independent in the wideband signal. The photons in these smaller subbands of the wideband signal can also be viewed as statistically independent. If we decrease the frequency bandwidth, we increase the coherence time. Thus measuring the signal over this subband equates to having a larger uncertainty in time. Hence when a photon is detected in this subband, due to the large coherence time we have that the knowledge of when this photon arrived is mostly lost. Making the time correlations irrelevant to a measurement of an integration time this long.

More insight has been gathered on the performance of the SPLITTER (Stationary spectrum Plus Low-rank Iterative TransmiTtance EstimatoR) algorithm as developed by Brackenhoff for denoising data gathered from observations of high-redshift galaxies. By using matrix decomposition to split the gathered data into a low-rank atmosphere matrix and a sparse matrix with the signal and photon noise, the algorithm avoids the subtraction of two noisy signals, and therefore the factor of √2 additional noise that comes with it. The algorithm was specifically developed for DESHIMA 2.0 (DEep Spectroscopic HIgh-redshift MApper), a wideband spectrometer that achieves a bandwidth from 220 to 440 GHz, using 347 spectral channels. Previous performance tests of the algorithm included the comparison of the weighted root mean square error between SPLITTER and the usual technique of Direct Subtraction on realistic data simulated using the TiEMPO (Time-dependent End-to-end Model for Post-process Optimization) software package. This resulted in a ~1.7 improvement factor for the whole spectrum and ~1.3 in the emission line area.

The performance of SPLITTER on two key components of the spectrum have been analyzed separately. First, the measurement of the continuum has been analyzed by using TiEMPO to create realistic simulations of the observation of custom spectra with a linear continuum. SPLITTER showed to be more precise as the noise level was lower, but less accurate, as there was a systematic offset in the estimated continuum. Using a modified black body model for the continuum and assuming the relative offset is independent of the strength of the continuum, the observed offsets and errors were propagated to offsets in estimations of dust temperature $T_{dust}$ and spectral emissivity of the dust $\beta$. Because of the offset, SPLITTER also showed a systematic offset in estimated $T_{dust}$, but as the algorithm is more precise, it performed better at estimating $\beta$, since $\beta$ determines the shape of the spectrum and has less influence on the strength. Second, to test the detection of emission lines, custom spectra have been created containing the same linear continuum and single spectral line at four different frequencies. Each line was set to have a known signal to noise ratio compared to the photon noise in its frequency bin. The retrieved signal to noise ratio as compared to noise of neighboring bins showed an improvement of ~1.9 for SPLITTER compared to Direct Subtraction for bright lines. Weak lines did not show any improvement in SNR. There seemed to be no correlation between continuum overestimation and emission line measurements.

Conclusion is that SPLITTER definitely shows improvement in noise reduction, but comes with an overestimation of the continuum. The consequences of this are that Direct Subtraction is still preferred for estimating dust temperature, but for estimations of spectral emissivity and detection of emission lines, SPLITTER is more robust.

DESHIMA (the Deep Spectroscopic High-Redshift Mapper) is a 347 channel superconducting spectrometer with spectral resolution R =500 that operates in the range of 220GHz to 440GHz and can therefore accurately measure the frequency of spectral lines in order to calculate redshift z.
This report investigates the sensitivity of DESHIMA-like spectrometers by investigating photon noise due to Poisson and bunching effects. It gives a broad overview of photon statistics and explains, through an analogous model, that photon bunching occurs due to an underlying change in the probabilistics, rather than the act of detecting itself. After that I investigate photon and quasiparticle recombination noise for a DESHIMA-like spectrometer with Lorentzian filters and find a closed form equation for NEP per channel for a constant power spectral density arriving at the filters.
Previously the bandwidth of the filters was assumed to be negligible, resulting in an overestimation of the bunching. Because the photons that are impinging on the detector span a bigger bandwidth, the bunching is a factor of π/2 smaller than previously approximated.
This NEPτ is defined at an integration time of τ=0.5s. For other integration times this is scalable, however this will only hold while the integration time is much bigger than the coherence time τ≫tcoh. Because of the correlation between photons arriving shorter than a coherence time apart, the scaling of the NEPτ drops in cases when τ≫̸tcoh.

Finally I propose and describe modifications to the sensitivity model DESHIMA uses. The following features have been be improved and added:

- Integrate over the entire power spectrum when calculating photon noise
- Use arbritatry filter designs loaded from a file
- Improve estimations of the quantities that express sensitivity

I compare the proposed modifications to the old model, which has previously been compared with measurement results, and use it to validate the changes. Other than the previously mentioned factor of π/2 for the bunching term and the smoothing out in local extrema, the modified simulation results are similar to the old model. This is because the Lorentzian filters have a small bandwidth ν≫Δν, such that the previous narrowband approximation held for most non-extreme cases.

Context. In the near-future, exoplanets can be observed directly through telescopes. Although the resolution of the planet's image will only be one pixel at first, the intensity of this pixel will change over time because of the orbit around its host star and its diurnal rotation. This intensity as a function of time is called the light curve of an exoplanet. The changes in the light curve as a result of annual and diurnal rotation can in turn be used to obtain information about the surface of the planet, this is called spin-orbit tomography.

Aims. The aim of this study is to determine if an exoplanet's surface can be retrieved from its light curve for planet surfaces that can be described by Lambertian, Lommel-Seeliger or Fresnel reflection, or a combination of these. The variation in the light curve due to differences in the planet's surface will be used to find a map of its continents and oceans and to determine what surface types the planet is made of.

Methods. This thesis starts by composing a near-equal area segmentation of a sphere to maximize the retrieval of information per pixel of the exoplanet's surface. Additionally, a method for generating artificial planets is described, such that the following method can be tested on light curves, since the current telescopes are not powerful enough to measure an exoplanet's light curve. A linear transformation from the surface to the light curve is constructed to obtain the light curve from the surface. Consequently, this transformation is inverted in order to obtain information about the surface from the light curve. This method is applied to exoplanets with a stationary surface, i.e. no clouds or changing ice caps and is consistent of the following surfaces: water, vegetation, sand and snow, each described by a different reflection model. Lastly, surface retrieval is tested from a light curve with a realistic amount of photon shot noise (SNR ≈ 14).

Results. The composed near-equal area segmentation of a sphere is the Voronoi diagram of the Fibonacci lattice. It is a very appropriate near-equal area segmentation, because the maximum difference in facet area is 12% for 1001 points. Furthermore, the retrieval of an exoplanet's surface from its reflected light curve is close to perfect for exoplanets that are described by a combination of the three reflection models if the light curve does not contain noise and there are a sufficient number of data points. If the light curve does contain shot noise, parts of the surface that are described by the Lommel-Seeliger law, are not retrieved correctly. However, the general shape of the surface that is described by Lambertian or Fresnel reflection is still retrieved correctly. If the surface can be described by one single reflection model, the planet's features are retrieved correctly from a light curve with shot noise regardless of the reflection model.

Conclusions. Spin-orbit tomography in the form of a linear transformation between the light curve and albedo map of an exoplanet is a very accurate method to retrieve the albedo map from a single observed pixel, even with a realistic amount of shot noise.

A gas-cell-based calibration setup was designed to evaluate the wideband response of sub-millimeter spectrometers like DESHIMA (DEep Spectroscopic High-redshift MApper). The use of low pressure gas emission spectra allowed for accurate calibration of the absolute frequency response, and to test the detectability of faint emission spectra with long integration times. This is important to understand and evaluate systematic errors and noise profiles of sub-millimeter astronomical spectrometers before their telescope campaigns.

The setup consisted of a low pressure (~mbar) gas at room temperature in a high vacuum (<10^-3 mbar) chamber in front of a 77K N₂ background. A double-winged rotating chopper was used for signal modulation of the on- and off-source paths to reduce the low-frequency noise profile. The setup has been able to successfully detect the emission spectra of nitrous oxide at 30 mbar and methanol at 1 mbar in the frequency range of 332 to 377 GHz with the prototype DESHIMA spectrometer. Our models showed that lower pressures should be detectable over similar averaging times. The standing spectrum showed to be too irregular for detecting spectral lines in a single measurement. A second measurement was required to subtract the standing features, which extended the total time required beyond the current system stability.

Detailed analysis into optical resonances has shown the importance of anti-reflective (AR) coatings on the main optical interfaces to improve the detectability of the emission spectra. We adapted sub-wavelength pyramid gratings milled into TOPAS windows to reduce a standing wave in the output spectrum of the gas cell setup. Stability of the setup was shown for observation times of up to ~10³ seconds before environmental
noises became dominant. Extensive stability testing has shown the impact of key components in the setup. A two-stage post-processing algorithm was developed to successfully reduce instabilities in the data by removing linear drifts and by removing the common profile over simultaneous read-out data.

Observing dust obscured high redshift galaxies is vital to understand the evolution of the early universe and the formation of stars and galaxies. HFLS3 is such a galaxy, and its emission spectrum can be detected at submillimeter wavelengths. With the Deep Spectroscopic High-redshift Mapper 2.0 (DESHIMA 2.0) it is pos- sible to observe these high redshift galaxies at the ASTE telescope in Chile. With the recently developed Time- dependent End-to-end Model for Post-process Optimization (TiEMPO) it is possible to simulate observations of DESHIMA2.0.
With TiEMPO it is possible to simulate different sky positions to accommodate different scenarios of wind direction. However, since TiEMPO is fairly new there are still some problems with the simulation of several of the the possible sky positions. More importantly, the model has to be tested with realistic high-redshift sources that are interesting for observations with DESHIMA 2.0. To predict whether a source can be observed with DESHIMA 2.0 it is necessary to estimate what the signal to noise ratio will be. Parameters like the pre- cipitable water vapor and the observation time determine if a source can be measured.
In this report, a solution is introduced to make it possible to use 6 different sky positions while simulating DESHIMA 2.0 measurements with TiEMPO. This solution is part of the current TiEMPO version, and can be used in future simulations.
With the improved model we simulate an observation of the dusty starburst galaxy HFLS3. The CII line in the emission spectrum is fainter than simulations done so far. A new model to simulate the emission spectrum was made to accommodate for this. With the use of beam switching some of the noise from the atmosphere is removed from the data. The simulation is compared to previously made observations as described in [2]. From the resulting signal we calculate the standard deviation σ to determine the signal to noise ratio (SNR). The values found for σ correspond well with the expected relation between σ and integration time. We say that a emission line is detected if the SNR is greater than 5. The calculated SNR of a 16 hour observation with a pwv value of 1.0 mm is 5.2, which shows that HFLS3 can be detected with DESHIMA 2.0. Two simulations of 8 hours with pwv values of 1.0 and 0.5 mm are compared as well. After 8 hours of observation, the SNR is 3.9 for a pwv value of 1.0 mm and 6.0 for a pwv value of 0.5 mm. With this lower pwv value the galaxy can be detected after 8 hours.
The analysis of this project can be repeated on other sources to make a database for future DESHIMA 2.0 simulations. Hereby it is key to have models which can predict the emission lines of a galaxy accurately.

We propose the Stationary spectrum Plus Low-rank Iterative TransmiTtance EstimatoR (SPLITTER) for removing wideband atmospheric noise from observations of high-redshift galaxies. This algorithm has specifically been developed for the DEep Spectroscopic HIgh-redshift MApper (DESHIMA) 2.0, a spectrometer that is designed to observe the waveband from 220 GHz to 440 GHz in 347 spectral channels. This octave bandwidth poses a challenge, due to the spectrotemporal changes in the atmosphere column between the instrument and the target source. Removing the time-varying nonlinear interference and distortion caused by the atmosphere is a difficult task, as the atmospheric emission is much stronger than a typical galaxy signal.

The goal of this thesis is to develop a method that can estimate both narrow spectral lines and the broad continuum emission with a higher sensitivity than the currently used method of directly subtracting noisy on- and off-source spectra. We develop a logarithmic data model for separating atmospheric noise from the galaxy signal in position switching-observations. Because the atmospheric transmittance appears as a multiplicative term in both the atmospheric interference and the signal modulation, the logarithmic model allows for an additive decomposition of the data. The atmospheric transmittance behaves as a low-rank component in this model.

Using the model, we develop an optimization algorithm (SPLITTER) to perform the separation of the signal and the low-rank atmospheric transmittance. Several implementations are discussed. The final algorithm uses a Singular Value Decomposition (SVD) to estimate the atmosphere component and the Alternating Directions Method of Multipliers (ADMM) for estimating the source signal. Instead of subtracting the noisy estimate of the source from the data directly, a denoised model is used in this step, such that we can trade some spectral resolution for a higher sensitivity.
SPLITTER is tested on simulated data using the Time-dependent End-to-end Model for Post-process Optimization of the DESHIMA spectrometer (TiEMPO), a dedicated software package for simulating DESHIMA observations. We show that SPLITTER is able to estimate the spectrum with a higher sensitivity than the conventional method. The improvement factor in our weighted root mean squared error is up to ~1.7 for the full spectrum and up to ~1.3 for the spectral lines only compared to the conventional method. The larger improvement for the full spectrum is achieved by trading spectral resolution for a higher sensitivity in the smooth continuum. With these results, we have an indication that a statistically driven method for DESHIMA observations can provide better estimates than the current method with the same amount of observing time.

More work is needed to create a robust version of the algorithm, because although the sensitivity benefit of SPLITTER is larger in the continuum regions, there are also situations where the continuum is overestimated. The conditions for this to occur are not yet clear. A more robust version could make SPLITTER a reliable new method that can replace current data reduction methods for wideband atmospheric noise removal. In this way, it can be used to make background-limited direct detection spectrometers on both existing and future telescopes observe more efficiently.

Superconducting integrated circuits (SICs) represent a natural step forward for devices operating at frequencies from microwave up to sub-millimeter wavelengths. They offer massive miniaturization via compact design based on low-loss superconducting transmission lines. At sub-millimeter wavelengths, the development of SICs is driven by astronomical instruments where it could allow the realization of an imaging spectrometer, combining simultaneous imaging and spectroscopy capabilities into a single instrument analogous to integral field units in the infrared and optical regimes. Such an imaging spectrometer can be achieved with SICs by integrating the required elements, such as spectral filters and polarizers, with the detectors onto a single chip. Without this integration, the dispersive system for even a single spatial pixel at these wavelengths would be prohibitively large and could not be realistically scaled up to allow imaging. Astronomical signals are exceedingly weak, typically requiring many nights of exposure to get a good signal to noise ratio. It is therefore imperative that the instrument has minimal losses before its detectors. As a consequence, the losses of each element in the SIC needs to be minimized, which requires careful characterization of the individual elements, including antenna, filters, detectors and connecting transmission lines. The primary focus of this thesis lies on the experimental characterization of the wideband antenna and the low-loss superconducting transmission lines.

In this report, we will focus on simulating galaxy observations with the Deep Spectroscopic High-redshift Mapper (DESHIMA). To do so, we will discuss and evaluate two main parts needed to accurately perform such a simulation:

Firstly, we will answer the question whether Time-dependent End-to-end Model for Post-process Optimization (TiEMPO), the modelling software used for DESHIMA observation simulations, is able to accurately simulate real life galaxy observations conditions. To do so, the simulation program is fed artificially created atmospheric data and its output is compared with sky brightness data of real measurements. More specifically, the time signal, power spectral density and noise equivalent flux density of both the simulation and the measurement data are derived and compared. This comparison showed, apart from a linear drift of the time signal data and a small offset of the power spectral density, good agreement between the simulation and the measurement.

The second part of this thesis discusses whether we can detect an artificially created galaxy, using the already verified atmospheric model of TiEMPO. To do so, the output of the simulation is run through a series of algorithms that calculate the observation spectrum of the telescope, as if it were a real measurement. In addition, the application of different observation tactics and telescope parameters are tested and visualised. Most importantly, two observational position-switching (chopping) techniques are applied and compared: the dual point and ABBA chopping techniques. To test the effectiveness of the two chopping techniques, both will be used to simulate atmospheric filtration using stationary, i.e. without telescope movement, simulation and measurement data, which do not contain the (to be detected) galactic data. As there is no telescope movement, nor galactic data, the spectra should ideally fluctuate around zero. However, as we will see in this report, this is not obtained in all cases. After further analysis, two main types of offsets could be identified: the first one originating from the linear drift of the measurement's time signal data, whereas the second one is due to the spatial displacement of the chopping positions. The former can be corrected by applying the ABBA chopping technique rather than the dual chopping method, whereas the latter cannot with either of the two.

Using the insights we acquire from running these simulations with observation conditions for DESHIMA, we are able to perform an actual galaxy observation simulation. The galactic data acquired from this observation simulation shows good agreement with the input values of the galaxy data of TiEMPO, assuring that TiEMPO can be used for galaxy observation simulations.

Ultra-wideband submillimeter observations are crucial to study the process of star and galaxy formation and for characterizing cosmic dust in the interstellar medium. The Deep Spectroscopic High-redshift Mapper 2.0 (DESHIMA 2.0) will use an integrated superconducting spectrometer chip with a 220-440 GHz band coverage and a spectral resolution of f/df = 500, enabling submillimeter observations with an unprecedented instantaneous band coverage.

However, the octave bandwidth of DESHIMA 2.0 poses a challenge: the atmospheric transmission is highly nonlinear in the broad frequency window of DESHIMA 2.0, complicating the removal of atmosphere noise from the signal.

In this thesis, I present the Time-dependent End-to-end Model for Post-process Optimization (TiEMPO). TiEMPO provides realistic time-dependent simulations of high-redshift galaxy observations. It consists of the following components:
Galaxy model. A galaxy is modeled using a two-component modified blackbody spectrum as a template. The model outputs the flux density, which is converted to power spectral density using the frequency-dependent effective aperture area of the telescope.
Atmosphere model. TiEMPO makes use of atmosphere model ARIS, which models a spatially and dynamically varying atmosphere and outputs Extra Path Length. TiEMPO converts this to precipitable water vapor using a relation that was found with the Smith-Weintraub value of the Extra Path Length and the ideal gas law.
Telescope beam. TiEMPO can be adapted to use any arbitrary beam shape for the near-field telescope beam. The far-field beam is modeled using the effective aperture area. Finally, the output of TiEMPO is given at multiple positions, enabling simulations of sky chopping and nodding in two directions.
Radiation transfer. A static model of the sensitivity of DESHIMA, determining the attenuation and the emission of the atmosphere and transmitting the signal through each component of the telescope and instrument.
Spectrometer chip. TiEMPO can adopt any filter transmission of the channels inside a spectrometer chip. In this work, they are approximated with Lorentzian curves. The photon and recombination noise are modeled with the NEP and the noise distribution is approximated with a normal distribution. The noise is incorporated with an integration over the filter response, treating photon-bunching over the wide bandwidth of DESHIMA 2.0 accurately.
Conversion to sky temperature.Finally, the power measured in the chip is related to the sky temperature with an interpolation made with a skydip simulation in the radiation transfer model.

We compare the first TiEMPO simulations to observation data by comparing the time signal, power spectral density and noise equivalent flux density. Apart from a small offset in the power spectral density, the simulation data closely resembles the observation data. TiEMPO allows us to test algorithms for atmosphere removal and galaxy detection, to study the effect of different weather conditions and to evaluate the performance of different observing techniques. TiEMPO is modular, making it usable for the original DESHIMA instrument and its successor DESHIMA 2.0. The use of TiEMPO can be extended to other spectrometers besides DESHIMA 2.0, like a grating spectrometer, and other telescopes, such as the promising 50m-aperture AtLAST/LST telescope.

The Deep Spectroscopic High-redshift Mapper, or DESHIMA, is an integrated superconducting spectrometer which measures the redshift of photons originating from submillimeter galaxies. These photons have to travel through the Earth's atmosphere before arriving at DESHIMA, but this atmosphere adds noise to the signal. Using a principal component analysis on still-sky measurement data, the influence of the atmospheric noise on these observations is analyzed. To achieve this, several principal component analyses are performed on still-sky observations, which are measurements of the brightness temperature of the sky, Tsky. These observations are assumed to be governed by three noise types: atmospheric noise, photon noise, and detector 1=f noise. A PCA on a still-sky observation reveals the effect of the most dominant noise sources. By creating an artificial data set, the physical origin of these noise sources can be found. This data set was produced by using an existing atmospheric model, based on the fluctuation of the precipitable water vapour, or PWV, in the atmosphere. A principal component analysis on this artificial data set reveals the effect of this PWV fluctuation on the data. The first principal component of the artificial data is found to represent the derivatives of the Tsky-PWV relations for every channel. The second principal component has a non-zero explained variance and is found to represent the second-order derivatives of the
Tsky-PWV relations for every channel, indicating that these relations are not linear. This can be explained by performing a Taylor expansion on the Tsky-PWV relation. Comparing the principal components of the real data to those of the artificial data shows that the first principal component generally has the same shape as the fist principal component of the artificial data, which represents the first-order PWV fluctuation, confirming that PWV fluctuation is the most dominant noise source for still-sky observations. It is also found that, when the PWV fluctuation is large, the second-order Taylor expansion term of the Tsky-PWV generally becomes more important in the real data. In this case, the first
principal component has a very high explained variance, and the second-order term is usually represented by the second principal component. Conversely, when the PWV range is small, the first-order term explains significantly less variance, and random noise like the photon noise becomes more dominant than the higher-order terms. The results show a few exceptions to this interpretation, so further research on these systematic errors is strongly recommended. In order to achieve better results, the experimental method can be improved by including the bandwidths of the channels and better estimation of the PWV fluctuation. This research can also be extended into a design of a random noise level and ultimately, the design of a better atmosphere calibration method for DESHIMA.

In this thesis we consider the reconstruction of albedo maps of exoplanets. This is done with a new variant of spin-orbit tomography that has been described in [Cowan and Agol, 2008] and more in depth in [Fujii and Kawahara, 2012]. This method reconstructs the albedo map from the reflected-light curve, the total intensity of the light that originates from the host star and is reflected by the planet. In the mentioned papers, the surface map of the planet is modeled as a sum of finite sized surface elements with constant albedo, and the relation between this approximation of the map and the light-curve in the time domain is determined. In this report, we use that the signal is quasi periodic due to diurnal and annual motion, and work with the Fourier peaks of the light-curve. We also approximate the map in a different way, writing it as the sum of spherical harmonics, and neglecting spherical harmonics with high spatial frequencies. This has the advantage that the relation can be worked out analytically (for edge-on and face-on observations) without the use of complex mathematics, and that both the surface map and the light-curve contain a daily frequency. We derive an equation for the reflective light-curve under the assumption that the surface map is not a function of time (no clouds), and that the reflection is Lambertian (equal in magnitude in all directions). This transformation is found to be a linear function of the surface map. This equation is worked out for edge-on and face-on observations with arbitrary axial tilt, which describes the orientation of the spin axis with respect to the observer and the orbital plane. Furthermore, we describe how to invert this relation if the axial tilt is known to the observer. We also aimed at recovering the map if the axial tilt is unknown to the observer, since this would make sure that the reconstruction does not rely on other observations. In contrast to what was found in papers like [Fujii and Kawahara, 2010] and [Fujii and Kawahara, 2012], we did not succeed in this. A number of methods were used for this. The first two looked at the problem from a mathematical perspective: the minimization of the distance between the measured light-curve and the light-curve from the reconstructed map, and Tikhonov regularization. The two failed because both the column space and the singular values respectively are not a function of the axial tilt. The third method that has been treated and tested involved the maximization of the ‘amount’ of positive albedo on the reconstructed map, but a test showed that the distinction that this method makes is in the same order of magnitude as the numerical error, thus proving that this method was not useful as well. Further study might show what causes the results of the two methods to differ in this respect

Superconducting resonators used in mm/sub-mm (MMW) astronomy would greatly benefit from deposited dielectrics with low dielectric loss. The excess loss in deposited dielectrics is mainly due to two-level systems (TLS), and there is no consensus on their microscopic origin. To study the relation between hydrogenated amorphous silicon’s (a-Si:H) microwave (MW) loss at 120 mK and its void volume fraction, hydrogen content, microstructure parameter, bond-angle disorder, and infrared (IR) refractive index, we deposited films at substrate temperatures of 100°C, 250°C and 350°C using plasma-enhanced chemical vapor deposition (PECVD). We measured the room temperature properties of the films using Fourier-transform infrared spectroscopy, Raman spectroscopy and ellipsometry. All room temperature properties except the IR refractive index decrease monotonically with increasing substrate temperature. The IR refractive index approaches the refractive index of crystalline silicon (c-Si) when increasing the substrate temperature to 350 °C. We measured the dielectric losses using superconducting coplanar waveguide resonators. Interestingly, we do not see a correlation of the room temperature results with the MW losses. All films have an excellent 120 mK MW loss tangent below 1e−5 at −50 dBm internal resonator power. More research on the loss tangents is recommended, for example using microstrip lines or lumped element parallel plate capacitors. The low dielectric losses make these films promising for application in MW kinetic inductance detectors and on-chip filters. These promising results could lead to the application of the dielectrics in the integrated superconducting spectrometer DESHIMA 2.0.

Sub-mm astronomy in space calls for an array of photon noise limited detectors, both for imaging and broadband spectroscopy. Microwave Kinetic Inductance Detectors (MKIDs), superconducting resonance circuits, are a suitable candidate for this purpose due to its multiplexing potential, but in literature excess noise in phase readout is encountered and attributed to so-called two-level systems (TLSs). Reduction in TLS induced noise and loss will provide greater flexibility in design and a route towards background limited detector performance.
In this thesis, TLSs from surface and bulk sources are modelled, so that their behaviour can be predicted through numerical computations of the field distributions inside the resonators. These calculations not only provide a guide for sensible chip designs, but allow for interpretation of experimental data and determination of dominant TLS sources.
It is found that for Al CPW resonators on Si or SiN, the noise is surface dominated but with a non-negligible bulk contribution, while for microstrips on a SiN membrane, the noise is bulk dominated. As the loss in microstrips for narrow microstrips is dominated by the substrate-air interface, the dominant TLS loss and noise sources do not necessarily coincide and should be treated independently. This makes it impossible to determine the dominant CPW surface noise contribution. Additionally, microstrips and CPWs on the same dielectric perform similarly, while Si is better than SiN, both in terms of loss and noise, due to a combination of SiN interface and bulk effects. Finally, material dependent loss and noise parameters have been determined and the importance of thorough Si surface cleaning has been established, yielding the best Al CPW noise ever encountered.
For sub-mm astronomy in space, the logical path to improvement would be the use of thorough cleaned Si as a dielectric, overetching and the use of LEKIDS and hybrid resonators, where microstrips are still viable for use. Importantly, having located the important TLS locations for various cases, tackling these problems areas further could provide the step towards background limited performance in space.