Modes of two-mirror cavity with non-coinciding main curvature directions

For a linear cavity, restricted by mirrors with distinct main directions of curvature, we have researched stability conditions and obtained explicit analytical formulae for a principal term of a basic mode. When the principal term of the fundamental mode cannot be uniquely determined, we obtain formulae for sets of solutions in a main approximation. Operators, transforming basic mode to higher modes, are expressed in terms of eigenvectors of 2×2 matrix, whose eigenvalues are responsible for stability conditions of the cavity.