A comprehensive model has been developed to study the operating characteristics of high-power high-brightness lasers consisting of a ridge-waveguide section coupled to a tapered region. The model, based on the Beam Propagation Method (BPM), includes a non-linear gain coefficient, current spreading due to junction voltage, and thermal effects taking into account for the first time to our knowledge a longitudinal gradient in the device temperature. We first demonstrate that during operation unwanted radiation that does not couple into the lateral mode of the waveguide, systematically propagates into the tapered region, and leads to the deterioration of the beam quality. To deflect and scatter this radiation, the use of specific cavity-spoiling elements, consisting of grooves etched down through the active region, appears necessary. We also study the role of the ridge section length in the operation of the device. A long ridge-waveguide region, providing both a well defined fundamental mode in the ridge-waveguide, and a gain saturation in the tapered region, improves the beam stability, but can lead, on the other hand, to optical self-focusing. Thermal effects are also investigated. We show how thermal lensing induces a lateral quadratic phase curvature and therefore alters the astigmatism of the device.
In this paper a compendium of InGaAs irradiation test results is presented. These photodiodes were irradiated either with γ γ γ γ-rays, protons, neutrons, electrons, pions, alpha particles or carbon ions of various energies. The displacement damage dose formalism was found to be effective in describing the radiation-induced dark current increase of any of the studied InGaAs photodiodes. The exploitation of capacitancebias voltage and current-bias voltage measurements also allows to deduce a damage factor that can be used to assess the radiation-induced dark current in a great number of radiation environments.Index Terms -Photodiodes, indium gallium arsenide devices, dark current, displacement damage.O. Gilard and M. Boutillier are with the French Space Agency CNES, 18 av Edouard Belin,
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.
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.
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