We have investigated the coupling between two-dimensional photonic crystals and a distributed Bragg reflector by fabricating silicon-based photonic crystals on top of a one-dimensional Bragg mirror. The two-dimensional photonic crystals contain Ge/ Si self-assembled islands as an internal source covering the 1.1-1.6 m spectral range. We show that we can control the quality factor of Bloch modes by varying the thickness of the silicon layer on top of the Bragg mirror. Quality factors up to 2200 are obtained for optical radiative modes collected from the surface for a photonic crystal with a square lattice pattern. The variation of the quality factor as a function of the thickness of the upper layer is confirmed by three-dimensional finite-difference time domain calculations of the investigated structures.
We report on silicon heterojunction solar cells using textured aluminum doped zinc oxide (ZnO:Al) as a transparent conductive oxide (TCO) instead of flat indium tin oxide. Double side silicon heterojunction solar cell were fabricated by radio frequency plasma enhanced chemical vapor deposition on high life time N-type float zone crystalline silicon wafers. On both sides of these cells we have deposited by radio frequency magnetron sputtering ZnO:Al layers of thickness ranging from 800 nm to 1400 nm. These TCO layers were then textured by dipping the samples in a 0.5% hydrochloric acid. External quantum efficiency as well as I-V under 1 sun illumination measurements showed an increase of the current for the cells using textured ZnO:Al. The cells were then annealed at 150• C, 175• C and 200• C during 30 min in ambient atmosphere and characterized at each annealing step. The results show that annealing has no impact on the open circuit voltage of the devices but that up to a 175• C it enhances their short circuit current, consistent with an overall enhancement of their spectral response. Our results suggest that ZnO:Al is a promising material to increase the short circuit current (Jsc) while avoiding texturing the c-Si substrate.
Aerosol quantification is of paramount importance for climate research, health and many other fields. The best method for measuring and characterizing aerosol from space is the application of a multi-angle polarimeter. A Dutch consortium has developed and delivered the so called SPEXone instrument for the NASA PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission, to be launched early 2024.SPEXone is based on the polarization modulation of the spectrum, allowing full characterization of the state of linear polarization of the incoming light. Earth is viewed under five angles, producing ten modulated spectra, projected on a single detector. A polarimetric accuracy of 0.3% is achieved, with the instrument of about 10 dm 3 volume and 10 kg mass.Based on the SPEXone design and experience, an upgraded instrument is being developed. Main change is the wider swath applied, from the 100 km swath for PACE to the present 250 km. This impacts the five telescopes, being integrated in one telescope unit.Other changes in the design are based on lessons learned, in particular the reduction and avoidance of stray light. The detector readout is adjusted for higher frame rate and more robust readout. These changes do not impact the instrument's budgets for mass, volume and power.In this paper, we will explain the principle of the SPEXone multi-angle spectropolarimeter instrument, the improvements with respect to the PACE version and its development status. The instrument can be flown as a stand-alone instrument for aerosol detection, as well as a support instrument where aerosol corrections are relevant, e.g., for high accuracy detection and quantification of methane and CO2.
A set of optical fiber assemblies has been developed and successfully qualified for its use on a European space science mission to the icy moons of Jupiter (Jupiter Icy Moons Explorer, JUICE), to be launched in 2022. The paper gives an overview of the design challenges, the test methods used for failure detection and screening of the optical fiber cable assemblies as well as the further testing performed in the frame of a lot acceptance qualification.
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