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Author

Bram Lap

Other affiliations: University of Groningen
Bio: Bram Lap is an academic researcher from Netherlands Institute for Space Research. The author has contributed to research in topics: Physics & Spectrometer. The author has co-authored 2 publications. Previous affiliations of Bram Lap include University of Groningen.

Papers
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Journal ArticleDOI
TL;DR: In this paper , the authors used a Dispersive Fourier Transform Spectrometer (DFTS) to measure the reflected RF signal from the tested NbTiN superconducting films at terahertz frequencies, allowing them to separate it from other reflections.
Abstract: We present the quality measurements of thick (thicker than London penetration depth) NbTiN superconducting films at Terahertz frequencies using a Dispersive Fourier Transform Spectrometer (DFTS). The reflected RF signal from the tested film was measured in time domain, allowing us to separate it from other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in superconducting state (film temperature below $Tc$) with that of the normal state (film temperature above $Tc$), we characterized the film quality at terahertz frequencies, and directly probed the energy of the superconducting gap of the tested film. The experimental results were fitted using the extended Mattis-Bardeen theory and th obtained film parameters show a good agreement with the literature. In addition to the DFTS, we have also measured the properties of NbTiN film using Time Domain Spectroscopy (TDS). It is shown that both TDS and DFTS provide similar results, and both techniques can be used for the quality control of thick NbTiN films. The superconducting gap determined from the measurements by both DFTS and TDS are in good agreement for both solid and meshed films showing that there is no remarkable degradation in the film quality due to technological processes of lift-off or ion etching.

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Proceedings ArticleDOI
28 Jun 2022
TL;DR: In this paper , the spectral and photometric imaging receiver (SPIRE) was used as a case study to highlight calibration issues observed in-flight, while including straylight. And the authors developed a modal framework to model, analyze, and address these issues.
Abstract: The next generation of astronomical space-based far-infrared (FIR) missions require ultra-sensitive spectroscopy as a diagnostic tool. These instruments use ultra-sensitive detector technologies to attain unprecedented levels of spectral observing sensitivity. The reception patterns of the individual detectors consist of individually coherent orthogonal field distributions, or equivalently, they are few-mode (5 to 20), to increase the spectral-spatial coupling to the astronomical source. However, the disadvantage of few-mode detectors is an increase in coupling to external (from the sky or warm telescope optics) and internal (from the instrument itself) straylight, which can greatly affect the measurement of the source spectrum. Therefore, understanding the spectral-spatial few-mode behavior of these systems in detail, and developing verification and calibration strategies, are crucial to ensure that the science goals of these future mission are met. Since conventional modelling techniques are less suited to address this problem, we developed a modal framework to model, analyze, and address these issues. In this paper, we use Herschel’s spectral and photometric imaging receiver (SPIRE) as a case study, because its optical design is representative for future FIR missions and illustrative to highlight calibration issues observed in-flight, while including straylight. Our analysis consist out of two part. In the first part, we use our modal framework to simulate the few-mode SPIRE Fourier transform spectrometer (FTS). In the second part, we carry out a end-to-end frequency-dependent partially coherent analysis of Herschel-SPIRE. These simulations offer a qualitative explanation for the few-mode behavior observed in-flight. Furthermore, we use the Herschel-SPIRE case-study to demonstrate how the modelling framework can be used to support the design, verification and calibration of spectrometers for future FIR missions. The modal framework is not only limited to the spectrometers discussed, but it can be used to simulated a wide range of spectrometers, such as low-resolution gratings and high-spectral resolution Fabry-Pérot interferometers.
Proceedings ArticleDOI
28 Aug 2022
TL;DR: In this article , the authors developed a modal framework, which uses the notion of optical modes, i.e. an unique set of individually coherent orthogonal field distributions, to propagate an incident electric field through an optical system.
Abstract: We have developed a modal framework [1], which uses the notion of optical modes, i.e. an unique set of individually coherent orthogonal field distributions, to propagate an incident electric field through an optical system. The framework relies on a transmission matrix and Singular Value Decomposition (SVD), to obtained the mode characteristics: their transmission efficiencies and spatial forms over the input and output surface of the optical system. Here, we present a VNA phase and amplitude measurement scheme used for determining the transmission matrix, and we compare the obtained mode characteristics to our model for a pair of limiting slits at 104 GHz, which show good agreement.