Abstract
In this paper, a new approximate formula of the fractional derivative is derived. The proposed formula is based on the generalized Laguerre polynomials. Global approximations to functions defined on a semi-infinite interval are constructed. The fractional derivatives are presented in terms of Caputo sense. Special attention is given to study the error and the convergence analysis of the proposed formula. A new spectral Laguerre collocation method is presented for solving linear fractional Klein-Gordon equation (LFKGE). The properties of Laguerre polynomials are utilized to reduce LFKGE to a system of ordinary differential equations, which solved using the finite difference method. Numerical results are provided to confirm the theoretical results and the efficiency of the proposed method.