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Department of Physics

Staff profile

Publication details for Dr Alastair Basden

MacLachlan, D. G., Harris, R. J., Gris-Sánchez, I., Morris, T. J., Choudhury, D., Gendron, E., Basden, A. G., Spaleniak, I., Arriola, A., Birks, T. A., Allington-Smith, J. R. & Thomson, R. R. (2017). Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy. Monthly Notices of the Royal Astronomical Society 464(4): 4950-4957.

Author(s) from Durham

Abstract

The spectral resolution of a dispersive astronomical spectrograph is limited by the trade-off between throughput and the width of the entrance slit. Photonic guided wave transitions have been proposed as a route to bypass this trade-off, by enabling the efficient reformatting of incoherent seeing-limited light collected by the telescope into a linear array of single modes: a pseudo-slit which is highly multimode in one axis but diffraction-limited in the dispersion axis of the spectrograph. It is anticipated that the size of a single-object spectrograph fed with light in this manner would be essentially independent of the telescope aperture size. A further anticipated benefit is that such spectrographs would be free of ‘modal noise’, a phenomenon that occurs in high-resolution multimode fibre-fed spectrographs due to the coherent nature of the telescope point spread function (PSF). We seek to address these aspects by integrating a multicore fibre photonic lantern with an ultrafast laser inscribed three-dimensional waveguide interconnect to spatially reformat the modes within the PSF into a diffraction-limited pseudo-slit. Using the CANARY adaptive optics (AO) demonstrator on the William Herschel Telescope, and 1530 ± 80 nm stellar light, the device exhibits a transmission of 47–53 per cent depending upon the mode of AO correction applied. We also show the advantage of using AO to couple light into such a device by sampling only the core of the CANARY PSF. This result underscores the possibility that a fully optimized guided-wave device can be used with AO to provide efficient spectroscopy at high spectral resolution.