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

Transdermal Blood Sampling for C-peptide Is a Minimally Invasive, Reliable Alternative to Venous Sampling in Children and Adults With Type 1 Diabetes

OBJECTIVE:C-peptide and islet autoantibodies are key type 1 diabetes biomarkers, typically requiring venous sampling, which limits their utility. We assessed transdermal capillary blood (TCB) collection as a practical alternative.RESEARCH DESIGN AND METHODS:Ninety-one individuals (71 with type 1 diabetes, 20 controls; individuals with type 1 diabetes: aged median 14.8 years [interquartile range (IQR) 9.1–17.1], diabetes duration 4.0 years [1.5–7.7]; controls: 42.2 years [38.0–52.1]) underwent contemporaneous venous and TCB sampling for measurement of plasma C-peptide. Participants with type 1 diabetes also provided venous serum and plasma, and TCB plasma for measurement of autoantibodies to glutamate decarboxylase, islet antigen-2, and zinc transporter 8. The ability of TCB plasma to detect significant endogenous insulin secretion (venous C-peptide ≥200 pmol/L) was compared along with agreement in levels, using Bland-Altman. Venous serum was compared with venous and TCB plasma for detection of autoantibodies, using established thresholds. Acceptability was assessed by age-appropriate questionnaire.RESULTS:Transdermal sampling took a mean of 2.35 min (SD 1.49). Median sample volume was 50 µL (IQR 40–50) with 3 of 91 (3.3%) failures, and 13 of 88 (14.7%) &lt;35 µL. TCB C-peptide showed good agreement with venous plasma (mean venous ln[C-peptide] – TCB ln[C-peptide] = 0.008, 95% CI [−0.23, 0.29], with 100% [36 of 36] sensitivity/100% [50 of 50] specificity to detect venous C-peptide ≥200 pmol/L). Where venous serum in multiple autoantibody positive TCB plasma agreed in 22 of 32 (sensitivity 69%), comparative specificity was 35 of 36 (97%). TCB was preferred to venous sampling (type 1 diabetes: 63% vs. 7%; 30% undecided).CONCLUSIONS:Transdermal capillary testing for C-peptide is a sensitive, specific, and acceptable alternative to venous sampling; TCB sampling for islet autoantibodies needs further assessment