The Seidel aberration coefficients of two mirror systems are derived analytically. By using these coefficients, the conditions for anastigmatic aplanats, flat field aplanats and compatible systems are investigated, also focusing capability for Gaussian beam is investigated in these systems.
In anastigmatic aplanats there are two types of systems, which are Couder type and inverse Cassegrainian type systems, and in flat field aplanats there are three types of systems, which are Schwarzschild type, Gregorian type and inverse Cassegrainian type systems, as compatible systems two types of systems are possible. They are inverse Cassegrainian type systems and systems composed of two concave mirrors, which are very similar to Schwarzschild systems. In the compatible systems the tangential field curvature is well corrected and the sagittal field curvature is also reasonable small.
As the Gaussian beam focusing system an inverse Cassegrainian system is chosen, as it is composed of spherical surfaces and satisfies anastigmatic conditions and compatible conditions. The final design of the Gaussian beam focusing system has 25 cm long focal length at F/1.25. The spot size at the Gaussian focal plane is 110 μm.
Intensity distributions at the focal plane are analyzed for both plane wave and Gaussian beam. The peak intensity of the Gaussian beam is 1.9 times the peak intensity of the plane wave at the focal plane. The intensity distribution changes due to defocusing are computed for both plane wave beam and Gaussian beam.
