Apodization in high-contrast long-slit spectroscopy. Closer, deeper, fainter, cooler

The spectroscopy of faint planetary-mass companions to nearby stars is one of the main challenges that new-generation high-contrast spectro-imagers are going to face. In a previous work we presented a long slit coronagraph (LSC), for which the presence of a slit in the coronagraphic focal plane induces a complex distribution of energy in the Lyot pupil-plane that cannot be easily masked with a binary Lyot stop. To alleviate this concern, we propose to use a pupil apodization to suppress diffraction, creating an apodized long slit coronagraph (ALSC). After describing how the apodization is optimized, we demonstrate its advantages with respect to the CLC in the context of SPHERE/IRDIS long slit spectroscopy (LSS) mode at low-resolution with a 0.12" slit and 0.18" coronagraphic mask. We perform different sets of simulations with and without aberrations, and with and without a slit to demonstrate that the apodization is a more appropriate concept for LSS, at the expense of a significantly reduced throughput (37%) compared to the LSC. Then we perform detailed end-to-end simulations of the LSC and the ALSC that include realistic levels of aberrations to obtain datasets representing 1h of integration time on stars of spectral types A0 to M0 located at 10 pc. We insert spectra of planetary companions at different effective temperatures (Teff) and surface gravities (log g) into the data at angular separations of 0.3" to 1.5" and with contrast ratios from 6 to 18 mag. Using the SD method to subtract the speckles, we show that the ALSC brings a gain in sensitivity of up to 3 mag at 0.3" with respect to the LSC, which leads to a much better spectral extraction below 0.5". In terms of Teff, we demonstrate that at small angular separations the limit with the ALSC is always lower by at least 100K, inducing an increase of sensitivity of a factor up to 1.8 in objects' masses at young ages. [Abridged]Comment: 15 pages, 17 figures. Accepted for publication in A&

On-sky multi-wavelength phasing of segmented telescopes with the Zernike phase contrast sensor

Future Extremely Large Telescopes will adopt segmented primary mirrors with several hundreds of segments. Cophasing of the segments together is essential to reach high wavefront quality. The phasing sensor must be able to maintain very high phasing accuracy during the observations, while being able to phase segments dephased by several micrometers. The Zernike phase contrast sensor has been demonstrated on-sky at the Very Large Telescope. We present the multi-wavelength scheme that has been implemented to extend the capture range from \pmlambda/2 on the wavefront to many micrometers, demonstrating that it is successful at phasing mirrors with piston errors up to \pm4.0 micron on the wavefront. We discuss the results at different levels and conclude with a phasing strategy for a future Extremely Large Telescope.Comment: 17 pages, 8 figures, 2 tables. Accepted for publication in Applied Optics; he final publised version is available on the OSA website: http://www.opticsinfobase.org/abstract.cfm?msid=13671

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor

Context. Several exoplanet direct imaging instruments will soon be in operation. They use an extreme adaptive optics (XAO) system to correct the atmospheric turbulence and provide a highly-corrected beam to a near-infrared (NIR) coronagraph for starlight suppression. The performance of the coronagraph is however limited by the non-common path aberrations (NCPA) due to the differential wavefront errors existing between the visible XAO sensing path and the NIR science path, leading to residual speckles in the coronagraphic image. Aims. Several approaches have been developed in the past few years to accurately calibrate the NCPA, correct the quasi-static speckles and allow the observation of exoplanets at least 1e6 fainter than their host star. We propose an approach based on the Zernike phase-contrast method for the measurements of the NCPA between the optical path seen by the visible XAO wavefront sensor and that seen by the near-IR coronagraph. Methods. This approach uses a focal plane phase mask of size {\lambda}/D, where {\lambda} and D denote the wavelength and the telescope aperture diameter, respectively, to measure the quasi-static aberrations in the upstream pupil plane by encoding them into intensity variations in the downstream pupil image. We develop a rigorous formalism, leading to highly accurate measurement of the NCPA, in a quasi-linear way during the observation. Results. For a static phase map of standard deviation 44 nm rms at {\lambda} = 1.625 {\mu}m (0.026 {\lambda}), we estimate a possible reduction of the chromatic NCPA by a factor ranging from 3 to 10 in the presence of AO residuals compared with the expected performance of a typical current-generation system. This would allow a reduction of the level of quasi-static speckles in the detected images by a factor 10 to 100 hence, correspondingly improving the capacity to observe exoplanets.Comment: 11 pages, 14 figures, A&A accepted, 2nd version after language-editor correction

Infusing COVID-19 into an undergraduate parasitology research course

The COVID-19 pandemic is a global event that has impacted both how and what educators teach. An unexpected outcome of the pandemic was the ability to enhance student understanding of public health through discussion of the novel coronavirus. Course-based undergraduate research experiences (CURE) provide students with authentic research experiences in the framework of an undergraduate course. Here the reconfiguration of the Parasitology Research course as an online CURE is discussed. This course included curriculum focused not only on parasite diagnostics, but also how it relates to diagnosing COVID-19 with the aim of helping students become scientifically prepared citizens

Assessment of a novel active packaging material to improve the resource efficiency of food production by increasing the safety and shelf life of perishable products

The objective of this thesis was the assessment of novel active packaging materials containing the polymer poly-[2-(tert-butylamino) methylstyrene] (poly(TBAMS)) for the application in perishable food supply chains. Furthermore, the potential of active packaging materials to increase the safety and shelf life of perishable products and thus to improve the resource efficiency of food production was assessed. The influence of food components, environmental factors, and different processing steps was analysed on the antimicrobial activity of 24 different processed materials containing poly(TBAMS). In total 714 samples containing poly(TBAMS) and 1032 references were investigated. Based on the results, certain kinds of packaging prototypes were produced for storage tests. 883 samples were tested in 15 storage trials with perishable product to assess the effect of poly(TBAMS) on product specific microbial, sensory, quality and chemical parameters. The modelling of the growth of spoilage and pathogenic bacteria, yeasts and moulds and the shelf life determination were conducted by using the modified Gompertz function. Based on all results, a standardized evaluation scheme for the assessment of active packaging materials` ability to increase the safety and shelf life of perishable foods were developed. Further an approach to analyse the cost and benefits by implementation of active packagings were developed. Calculations were exemplified for poly(TBAMS) packagings. Different materials containing poly(TBAMS) showed a high antimicrobial activity against spoilage and pathogenic organisms relevant for perishable products. The food components (especially proteins), temperature, gas atmosphere and the processing of the polymer itself influenced the activity. The activity depended on the availability of functional groups of poly(TBAMS) on the polymeric surface, which increased by increasing the concentration or enlarging the surface. A multilayer foil containing 15 % of poly(TBAMS) in the inner layer increased the microbial safety and shelf life of products with low protein contents, such as R-T-E vegetables, and of processed meat products. Thus, the novel packaging solutions have high potential to reduce food waste by increasing the safety and shelf life of perishable foods. The developed evaluation scheme allows the identification of the application area where an active material delivers the highest benefit during the development phase. The cost–benefit analysis represents a new approach for the calculation of the economic and resource-efficient impact by implementation of different active packaging materials. Both can lead to a reduction of time and costs during developing of antimicrobial packaging materials.Bewertung eines neuartigen aktiven Verpackungsmaterials zur Steigerung der Ressourceneffizienz der Lebensmittelproduktion durch eine Erhöhung der Sicherheit und Haltbarkeit leichtverderblicher Produkte Ziel der Arbeit war die Bewertung neuartiger aktiver Verpackungsmaterialien auf Basis von poly-[2-(tert-butylamino) methylstyrene] (poly(TBAMS)) hinsichtlich der Anwendung in Wertschöpfungskette für leichtverderbliche Lebensmittel. Weiterhin wurde im Rahmen der Arbeit eine standardisierte Vorgehensweise entwickelt, um das Potential von aktiven Verpackungen zur Erhöhung der Sicherheit und Haltbarkeit leicht verderblicher Produkte sowie deren Beitrag zur Verbesserung der Ressourceneffizienz zu bewerten. Für die Bewertung des neuen Polymers wurde der Einfluss von Lebensmittelinhaltsstoffen, Umweltfaktoren und verschiedener Verfahrenstechniken bei der Herstellung der Verpackungsmaterialien auf die antimikrobielle Aktivität analysiert. Insgesamt wurden 714 poly(TBAMS) enthaltende Materialproben und 1032 Referenzen untersucht. Basierend auf den Ergebnissen erfolgte die Herstellung verschiedener Folien und Vliese für die Lagerungstests. 883 Proben wurden in 15 Zeitreihen mit leicht verderblichen Lebensmitteln getestet, um den Effekt von poly(TBAMS) auf produktspezifische Parameter zu bewerten. Die Modellierung des Wachstums verschiedener Bakterien, Hefen und Pilze, und die Ermittl-ung der Haltbarkeitszeiten erfolgte mit der modifizierten Gompertzfunktion. Auf Grundlage aller Analysen wurde ein Prüfschema zur Bewertung aktiver Materialien im Hinblick auf ihre Eignung, die Haltbarkeit leicht verderblicher Lebensmittel zu erhöhen, entwickelt. Zudem wurde eine Vorgehensweise entwickelt, um die Kosten und Nutzen von aktiven Verpackungen für die unterschiedlichen Stufen der Wertschöpfungskette zu berechnen. Verschiedene poly(TBAMS) enthaltende Materialen zeigten eine hohe antimikrobielle Aktivität gegen eine Vielzahl Verderbnis erregende und pathogene Bakterien. Einige Lebensmittelinhaltstoffe (insbesondere Proteine), die Temperaturbedingungen und die Compoundierung des Polymers mit verschiedenen Matrixpolymeren beeinflussten die Wirksamkeit. Die Aktivität des Polymers konnte mit der Erhöhung der Konzentration von poly(TBAMS) oder durch eine größere Polymeroberfläche gesteigert werden. So zeigte eine Mehrschichtfolie mit 15 % poly(TBAMS) in der Innenschicht eine Haltbarkeitsverlängerung bei Fleischprodukten und bei proteinarmen Lebensmitteln, wie zum Verzehr fertiges Gemüse. Das entwickelte Prüfschema sowie die Kosten-Nutzen Analyse ermöglichen es, geeignete Anwendungsgebiete antimikrobieller Polymere schon während der Entwicklungsphase zu identifizieren. Dadurch können die Entwicklungszeiten und -kosten deutlich reduziert werden und durch verlängerte Haltbarkeitszeiten wichtige Ressourcen geschont werden