Influence of superluminality in Gaussian beam on Q-factor of the open resonator modes

For the two-dimensional open resonator (OR) with cylindrical mirrors in strict statement of a problem of diffraction is explored an influence of Gaussian beam parameters on Q-factor of the fundamental and higher modes. It is established, that the superluminality in Gaussian beam reduces in a raise of Q-factor of the OR modes in comparison with traditional estimations. For the fundamental mode the discrepancy in Q-factor makes up to 2%, and for higher modes reaches 20%, that it is necessary to take into account at electromagnetic measuring.