Over the last two decades, high-precision photometry with the Hubble Space Telescope (HST) revealed that many globular clusters, previously regarded as prime examples of pristine coeval systems, in fact, host multiple populations of stars with different ages and chemical abundances. The origin of this population multiplicity remains under debate. Detailed analysis of globular cluster photometry is further complicated by the relative importance of enhancements of individual chemical elements and the corresponding deficit of model atmospheres for non-solar abundances in literature. We present our analysis of new HST WFC3/IR observations of the globular cluster NGC 6752, presently known to host three distinct main sequences with varying metallicities, helium mass fractions and non-solar element enhancements. We calculate a new grid of model atmospheres and evolutionary models, specifically tailored to the properties of those three populations, inferred from the spectroscopic analysis of the brightest members of the cluster in the literature and iteratively adjusted to achieve the best correspondence with the observed colour-magnitude diagram. The observed luminosity function of the cluster is combined with the theoretical mass-luminosity relations computed from our models to derive constraints on the initial mass function (IMF) of the cluster. We find a discrepancy between spectroscopic and photometric abundances of oxygen and aluminum in the most metal-poor population. The IMF is well approximated by a broken power law relationship with no significant evidence of variability in parameters among the populations. We extend the model grid beyond the faint limit of the currently available data into the substellar regime and make specific predictions of colours and magnitudes of brown dwarfs in each of the three sequences that may be observed with next generation facilities including James Webb Space Telescope (JWST).

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