The mathematical details of a family of inverse Fourier transform techniques to uniquely recover the second-order optical nonlinearity profile of thin films are discussed both theoretically and numerically. These methods are all based on the Maker-fringe technique, i.e., they involve focusing a fundamental laser beam onto a nonlinear film and measuring the generated second-harmonic power as a function of the incidence angle of the fundamental beam. It is shown that each method can be treated as a special case of a general theory. An error analysis for the recovery of theoretical nonlinearity profiles is also illustrated with numerical examples.