Kramers-Kronig analysis of the optical linearity and nonlinearity of nanostructured Ga-doped ZnO thin films

•Sol-gel spin coating technique is used to prepare pure and Ga-ZnO samples.•First time Kramers-Kronig equations are used to calculate linear and related nonlinear optical parameters.•Ga showed considerable effect on various physical parameters.•High values of χ(1), χ(3) and n(2) were observed for Ga doped ZnO samples.•All the linear and nonlinear parameters quite high compare to previous reports.