Solar flares are transient, yet dramatic energy release events in the Sun’s atmosphere that, together with the closely associated phenomenon of coronal mass ejections (CMEs), form a fundamental part of geo-effective space weather. Since their first discovery in 1859, substantial efforts have been made in understanding the energetics of flares. However there remains outstanding questions concerning the ways in which energy is released and transported in flares. We propose a comprehensive project targeted at advancing our understanding of flare energy deposition into the solar chromosphere. This project will focus on spectral lines of orthohelium, which have been shown to exhibit the unusual characteristic of initially dimming in the earliest stages of energy deposition into the lower atmosphere, before then brightening. These dimmings have been shown to be related to the properties of non-thermal particles present in flares. Using a combination of exceptionally high spatial resolution imaging spectroscopy of the He I 10830 Å and D3 5876 Å lines (via the 1.6m BBSO/GST) and state-of-the-art radiation hydrodynamic modelling (RADYN and RH codes) we will: 1) Take new observations using GST and perform analysis of the spatial and spectral characteristics of flare emission and enhanced absorption of the He I 10830 Å and D3 5876 Å, both individually and in relation to each other; and 2) Determine if our models are consistent with those observations, in terms of contrast level, the