arXiv subjects

B. N. R. Lap

Publications and source records attributed to B. N. R. Lap.

3 recordsLinked to original sources

arXiv2022

Modal Simulation Framework for the Design and Verification of Future Few-Mode Far-Infrared Spectrometers

Future far-infrared space missions require highly-sensitive spectroscopy as a primary diagnostics tool. However, these systems are sensitive to straylight, due to the ultra-sensitive few-mode detectors used, which affects the measurement and calibration of the spectrum, as revealed by the Herschel mission. To ensure that the science goals of future missions are met, the complex modal behaviour has to be understood, and appropriate verification and calibration strategies must be developed. We propose a modal framework to addresses these issues, using Herschel-SPIRE as a case study, and demonstrate how the technique can be used for the design and verification of spectrometers in future far-infrared missions.

astro-ph.IM↗

arXiv2022

Modelling the Partially Coherent Behaviour of Few-Mode Far-Infrared Grating Spectrometers

Modelling ultra-low-noise far-infrared grating spectrometers has become crucial for the next generation of far-infrared space observatories. Conventional techniques are awkward to apply because of the partially coherent form of the incident spectral field, and the few-mode response of the optics and detectors. We present a modal technique for modelling the behaviour of spectrometers, which allows for the propagation and detection of partially coherent fields, and the inclusion of straylight radiated by warm internal surfaces. We illustrate the technique by modelling the behaviour of the Long Wavelength Band of the proposed SAFARI instrument on the well-studied SPICA mission.

astro-ph.IM↗

arXiv2021

Characterization of superconducting NbTiN films using a Dispersive Fourier Transform Spectrometer

We have built a Terahertz Dispersive Fourier Transform Spectrometer \cite{Birch1987} to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below $T_c$) with the reflection of the normal state, we characterise the film quality at terahertz frequencies. The method was applied to 70 and 200nm thick Nb films on a silicon wafer and to 360nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, $α$, was found to be 3.52 for Nb, and 3.71-4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory \cite{Noguchi2012} and show a good agreement.

cond-mat.supr-con↗