Investigation and minimization of aberrations in two-mirror imaging system

A formula for the eikonal in the aperture of an axially symmetric two-mirror imaging system is obtained for the case when the source is arbitrarily displaced from the focus. The formula yields a result accurate to the cubed value of this displacement. The Newton method is applied to find a correction improving the formula for the eikonal. On the basis of the derived formula for the eikonal, the amplitude distribution and the distribution of inclination angles of rays reflected by the main mirror are found. The astigmatism value is estimated, and formulas for the relationship of an axially symmetric two-mirror imaging system parameters that minimizes this value are presented. As an example of application of the theory, a terahertzband scanning imaging system is optimized. The simulation is performed to demonstrate the possibility of realizing a view angle exceeding 15 degrees.