Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy

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.

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.

Citation

MacLachlan, D., Harris, R., Gris-Sánchez, I., Morris, T., Choudhury, D., Gendron, E., …Thomson, R. (2017). Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy. Monthly Notices of the Royal Astronomical Society, 464(4), 4950-4957. https://doi.org/10.1093/mnras/stw2558

• Journal Article Type: Article
• Acceptance Date: Oct 6, 2016
• Online Publication Date: Oct 6, 2016
• Publication Date: Feb 1, 2017
• Deposit Date: Jul 26, 2017
• Publicly Available Date: Jul 26, 2017
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 464
• Issue: 4
• Pages: 4950-4957
• DOI: https://doi.org/10.1093/mnras/stw2558