Declare spectrum amplitude functions (`_f_Gauss`, `_f_Airy`, `_f_Gauss_cartesian`, `_f_Laguerre_Gauss_cartesian`, `_f_Gauss_spherical` and `_f_Laguerre_Gauss_spherical`) as static methods.
Declare spectrum amplitude functions (
_f_Gauss,_f_Airy,_f_Gauss_cartesian,_f_Laguerre_Gauss_cartesian,_f_Gauss_sphericaland_f_Laguerre_Gauss_spherical) as static methods.