A new method for correcting fibre barycentre displacements in high resolution spectroscopy

摘要

Unpredictable displacements in the photocentre of an optical feed at the entrance slit of a spectrograph producecorresponding barycentre offsets that impose limits to very high resolution schemes. These limitations not only apply todirect light from a science object, but also light relayed via an optical fibre or image slicer. Several mitigation strategiesare in development or are currently in use, however these all have potentially restrictive idiosyncrasies.An alternative approach is proposed to remove displacement effects from the spectra by nulling barycentre offsets.Correction is achieved by time-integrating at the detector a sequence of multiple normal and 180-degree inverted imagesof the input aperture, thus eliminating optical asymmetries about the axis of inversion, which is aligned orthogonal to thespectral direction. The flip is generated with a path-length compensated, non-dispersive ‘reversion prism’, driven on ahigh precision translation stage. The prism is periodically chopped in and out of the beam, and the resulting time-averagedimage thus has an imposed central axis regardless of barycentre shifts.The method works regardless of the specifics of the spectrograph feed (fibre, multiple fibres, slit, slicer etc.) With arelatively simple and inexpensive scheme it should be possible to stabilise an image to better than one part in 10sup4/sup potentially permitting detection down to cmssup-1/sup regimes.The concept is currently at a very early stage of development, so this paper outlines the basic principles and details apractical reversion component that is currently under development at Durham CfAI. There then follows a description ofhow the component will be implemented in a laboratory prototype scheme. The paper concludes with a proposed testplan and suggests the focus for future work.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.