Recovering density disturbance spectra from FLDI. Part 2: comparisons with previous methods

An exact analytical method for recovering density disturbance spectra in multi-frequency, multi-dimensional fields from focused laser differential interferometry (FLDI) measurements, developed in Part 1 [Appl. Opt.62, 3042 (2023)APOPAI0003-693510.1364/AO.480352], is compared with previous methods for quantitative interpretation of FLDI. It is shown that previous exact analytical solutions can be recovered as special cases of the more general present method. It is also found that despite outwards dissimilarity, a previous approximate method that is becoming widely used can be related to the general model. It is demonstrated that the previous approach-while a suitable approximation for spatially restricted disturbance fields such as conical boundary layers it was originally applied to-does not work well in general applications. While corrections can be made, informed by results from the exact method, doing so offers no computational or analytical advantages.