Evaporated Afnia thin film suffer of high porosity that causes the variation of the optical parameters when the film is exposed to the atmosphere. The ion beam assisted deposition is a useful method to obtain dense and adherent thin film. In this work, the effect of the (Xe) low energy ion beam assistance on the optical properties of HfO2 thin film is investigated. The deposition parameters are expressed in terms of momentum transfer per arrival atoms. Dense films were obtained increasing the P value. The Sigmund's model was applied to describe the collision cascade mechanism and to calculate the threshold energy at which no sputtering occurs. The experimental measurements of sputtering yield were compared with the calculated values. Assisting the growing film by Xe ions at energy lower than the energy threshold, an high value of refractive index has been obtained, as well as for the sample assisted at high P values.