Gallium is a liquid metal at near room temperature and in recent decades has become a key element in both electronic and optoelectronic applications. We demonstrate for the first time highly ordered spherical Ga nanoparticle (NP) arrays were fabricated by glancing angle deposition (GLAD) technique. GLAD is a simple method based on self-assembly that can produce highly ordered one-dimensional plasmonic NP chains. The real time (in-situ) monitoring of optical properties of Ga NPs plays an important role in measurement of optical behaviour in phase change. Also this provides information on the growth mechanism and allows production of structures with the desired optical characteristics. Reflectance anisotropy spectroscopy (RAS) has been used for monitoring of in-situ optical properties of the liquid-solid transition in Ga NP arrays. The results show stability and phase transition sensitivity of plasmonic resonance of Ga NP arrays. In order to confirm experimental results an analytical model was adapted by using Transfer Matrix Formalism and experimental parameters of Ga NP arrays were used for simulation.