A new approach to classical spectroscopy

Abstract

In this thesis I demonstrate a new approach to classical fibre-fed spectroscopy. My method is to use a photonic lantern device that converts an arbitrary (e.g. incoherent) input beam into N diffraction-limited outputs. For the highest throughput, the number of outputs must be matched to the total number of unpolarised spatial modes on input. This approach has many advantages: (i) after the lantern, the instrument is constructed from ‘commercial off the shelf’ components; (ii) the instrument is the minimum size and mass configuration at a fixed resolving power and spectral order; (iii) the throughput can be better than 60% (slit to detector, including detector QE of ~80%); (iv) the scattered light at the detector can be less than 0.1% (total power). I have designed and built 3 such instruments, one operating in the infrared and two operating in the visible wavelengths of light. What follows is a study of the design implications for such a spectrograph, and an experimental exploration of their characteristics. I also present a versatile data reduction package I have developed in tandem with the instruments.