The problem of an intracavity lasing of the laser with an external reflector under conditions of spatial mismatch between the incident and reflected waves is discussed. A system of equations is derived for the coefficients of series expansion of the light field in the eigenfunctions of an empty resonator in the case of a spatially homogeneous active medium. The derivation was made within the framework of semiclassical theory of quantum generators. A comparison of techniques for recording the optical fields using heterodyne detection and coherent laser detection. It is shown that these techniques differ only by the shapes of the transmission functions of the detectors, which in the latter case is described by the eigenfunctions of the empty resonator.