Modal noise mitigation in a photonic lantern fed near-IR spectrograph

Recently we have demonstrated the potential of a hybrid astrophotonic device, consisting of a multi-core fiber photonic lantern and a 3D waveguide reformatting component, to efficiently reformat the multimode point spread function of a telescope to a diffracted limited pseudo-slit. Here, we report on an investigation into the potential of this device to mitigate modal noise-one of the main hurdles of multi-mode fiber-fed spectrographs. The modal noise performance of the photonic reformatter and other fiber feeds was assessed using a bench-Top spectrograph based on an echelle grating. In a first method of modal noise quantification, we used broadband light as the input, and assessed the modal noise performance based on the variations in the normalized spectrum as the input coupling to the fiber feed is varied. In a second method, we passed the broadband light through an etalon to generate a source with spectrally narrow peaks. We then used the spectral stability of these peaks as the input coupling to the fiber feed was varied as a proxy for the modal noise. Using both of these approaches we found that the photonic reformatter could significantly reduce modal noise compared to the multi-mode fiber feed, demonstrating the potential of photonic reformatters to mitigate modal noise for applications such as near-IR radial velocity measurements of M-dwarf stars. </p

Microcracks in CVD diamond produced by scaife polishing

We investigate sub-surface damage in a CVD diamond, polished on a (110) plane using the traditional scaife method. The damage lies in tracks that consist of microcracks lying perpendicular to the polishing direction. These cracks have an irregular spacing and are comprised mainly of {111} facets. Their geometry is consistent with a modified Hertzian fracture, caused by a stick-slip movement of relatively large (micron-sized) diamond particles on the scaife. The interior surface of the cracks shows a 1x1 CH3 surface reconstruction, consistent with a high hydrogen overpressure that results from ingress of hydrocarbons in the polishing lubricant and a relatively low temperature process. The crack edge is ragged, and voids with sizes of a few nm are found up to hundreds of nm from the crack front, particularly where the crack ends at the polished surface. We propose that these features are evidence of significant healing of the cracks once the applied stress is removed. Luminescence at the crack tips is seen, presumably due to impurities trapped in these voids, which quenches with electron irradiation at 10 keV

Multi-core fibre-fed integral field spectrograph (MCIFU) IV:The fiber link

The Multi-Core Integral-Field Unit (MCIFU) is a diffraction-limited near-infrared integral-field spectrograph designed to detect and characterise exoplanets and disks in combination with extreme adaptive optics (xAO) instruments. It has been developed by an extended consortium as an experimental path finder for medium resolution spectroscopic upgrades for xAO systems. To allow it to achieve its goals we manufactured a fibre link system composed of a custom integrated fiber, with 3D printed microlenses and an ultrafast laser inscribed reformatter. Here we detail the specific requirements of the fibre link, from its design parameters, through its manufacture the laboratory performance and discuss upgrades for the future. © 2020 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The kaleidoscopic midwife: A conceptual metaphor illustrating first-time mothers' perspectives of a good midwife during childbirth. A grounded theory study

Background: The literature review reveals general information about a good midwife from a range of perspectives and what childbearing women generally value in a midwife, but there is a lack of information around mothers’ perspectives of what makes a good midwife specifically during labour and birth, and even less in the context of different places of birth. Aim: To conceptualise first-time mothers’ expectations and experiences of a good midwife during childbirth in the context of different birthplaces. Design: Qualitative Straussian grounded theory methodology. Setting: Three National Health Service Trusts in England providing maternity care that offered women the possibility of giving birth in different settings (home, freestanding midwifery unit and obstetric unit). Participants: Fourteen first-time mothers in good general health with a straightforward singleton pregnancy anticipating a normal birth. Methods: Ethical approval was gained. Data were collected through two semi-structured interviews for each participant (before and after birth). Data analysis included the processes of coding and conceptualising data, with constant comparison between data, literature and memos. Findings: The model named ‘The kaleidoscopic midwife: a conceptual metaphor illustrating first-time mothers’ perspectives of a good midwife during childbirth’ was developed. The model is dynamic and woman-centred, and is operationalised as the midwife adapts to each woman's individual needs in the context of each specific labour. Four pillars of intrapartum care were identified for a good midwife in the labour continuum: promoting individuality; supporting embodied limbo; helping to go with the flow; providing information and guidance. The metaphor of a kaleidoscopic figure is used to describe a midwife who is ‘multi-coloured’ and ever changing in the light of the woman's individual needs, expectations and labour journey, in order to create an environment that enables her to move forward despite the uncertainty and the expectations-experiences gap. The following elements are harmonised by the kaleidoscopic midwife: relationship-mediated being; knowledgeable doing; physical presence; immediately available presence. Conclusion: The model presented has relevance to contemporary debates about quality of care and place of birth and can be used by midwives to pursue excellence in caring for labouring mothers. Independently from the place of birth, when the woman is cared for by a midwife demonstrating the above characteristics, she is likely to have an optimum experience of birth. Future research is necessary to tease out individual components of the model in a variety of practice settings

Multi-core fibre-fed integral-field unit (MCIFU):Overview and first-light

The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder for spectroscopic upgrades for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0 um to 1.6um at a resolving power around 5000 for 73 points on-sky. The MCIFU uses novel astrophotonic components to make this very compact and robust spectrograph. We performed the first successful on-sky test with CANARY at the 4.2 meter William Herschel Telescope in July 2019, where observed standard stars and several stellar binaries. An improved version of the MCIFU will be used with MagAO-X, the new extreme adaptive optics system at the 6.5 meter Magellan Clay telescope in Chile. We will show and discuss the first-light performance and operations of the MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.</p

matscipy : materials science at the atomic scale with Python

Behaviour of materials is governed by physical phenomena that occur at an extreme range of length and time scales. Computational modelling requires multiscale approaches. Simulation techniques operating on the atomic scale serve as a foundation for such approaches, providing necessary parameters for upper-scale models. The physical models employed for atomic simulations can vary from electronic structure calculations to empirical force fields. However, construction, manipulation and analysis of atomic systems are independent of the given physical model but dependent on the specific application. matscipy implements such tools for applications in materials science, including fracture, plasticity, tribology and electrochemistry

The impact of red deer on liverwort-rich oceanic heath vegetation

Background: There is concern about increasing numbers of large herbivores including red deer (Cervus elaphus) but little is known about their impact on bryophytes. Aims: This study set out to determine the effect of different localised densities of red deer on the internationally important Northern Atlantic hepatic mat, characteristic of oceanic heath vegetation, at four locations in the Scottish Highlands where sheep have been absent for decades. Methods: Thirty 7 m x 7 m plots were randomly located in each study area. The standing crop dung pellet group count method was used to estimate red deer density. Species richness, diversity and cover of hepatic mat liverworts were obtained from 1 m x 1 m quadrats placed at random within the sample plots. Calluna vulgaris cover, ericoid height, rock cover, gradient and altitude were also recorded. Results: Model simplification in ANCOVA revealed a consistent pattern of decreasing cover of hepatic mat and Calluna with increasing red deer density at all four study areas. Northern Atlantic hepatic mat cover, diversity and species richness were positively correlated with Calluna cover. Conclusions: The data suggest that Calluna cover is reduced (through trampling and browsing) at high local densities of red deer which has had cascading effects on the Northern Atlantic hepatic mat. Alternative explanations are discussed

Modal noise mitigation for high-precision spectroscopy using a photonic reformatter

Recently, we demonstrated how an astrophotonic light reformatting device, based on a multicore fibre photonic lantern and a three-dimensional waveguide component, can be used to efficiently reformat the point spread function of a telescope to a diffraction-limited psuedo-slit [arXiv:1512.07309]. Here, we demonstrate how such a device can also efficiently mitigate modal noise -- a potential source of instability in high resolution multi-mode fibre-fed spectrographs). To investigate the modal noise performance of the photonic reformatter, we have used it to feed light into a bench-top near-infrared spectrograph (R {\approx} 9,500, {\lambda} {\approx} 1550 nm). One approach to quantifying the modal noise involved the use of broadband excitation light and a statistical analysis of how the overall measured spectrum was affected by variations in the input coupling conditions. This approach indicated that the photonic reformatter could reduce modal noise by a factor of six when compared to a multi-mode fibre with a similar number of guided modes. Another approach to quantifying the modal noise involved the use of multiple spectrally narrow lines, and an analysis of how the measured barycentres of these lines were affected by variations in the input coupling. Using this approach, the photonic reformatter was observed to suppress modal noise to the level necessary to obtain spectra with stability close to that observed when using a single mode fibre feed. These results demonstrate the potential of using photonic reformatters to enable efficient multi-mode spectrographs that operate at the diffraction limit and are free of modal noise, with potential applications including radial velocity measurements of M-dwarfs.Comment: 13 pages, 9 figures (including appendix