Image degradation due to surface scatter in the presence of aberrations.

Image analysis in the presence of surface scatter due to residual optical fabrication errors is often perceived to be complicated, nonintuitive, and achieved only by computationally intensive nonsequential ray tracing with commercial optical analysis codes such as ASAP, Zemax, Code V, TracePro, or FRED. However, we show that surface scatter can be treated very similarly to conventional wavefront aberrations. For multielement imaging systems degraded by both surface scatter and aberrations, the composite point spread function is obtained in explicit analytic form in terms of convolutions of the geometrical point spread function and scaled bidirectional scattering distribution functions of the individual surfaces of the imaging system. The approximations and assumptions in this formulation are discussed, and the result is compared to the irradiance distribution obtained using commercial software for the case of a two-mirror telescope operating at an extreme ultraviolet wavelength. The two results are virtually identical.

Linear systems formulation of scattering theory for rough surfaces with arbitrary incident and scattering angles.

Scattering effects from microtopographic surface roughness are merely nonparaxial diffraction phenomena resulting from random phase variations in the reflected or transmitted wavefront. Rayleigh-Rice, Beckmann-Kirchhoff. or Harvey-Shack surface scatter theories are commonly used to predict surface scatter effects. Smooth-surface and/or paraxial approximations have severely limited the range of applicability of each of the above theoretical treatments. A recent linear systems formulation of nonparaxial scalar diffraction theory applied to surface scatter phenomena resulted first in an empirically modified Beckmann-Kirchhoff surface scatter model, then a generalized Harvey-Shack theory that produces accurate results for rougher surfaces than the Rayleigh-Rice theory and for larger incident and scattered angles than the classical Beckmann-Kirchhoff and the original Harvey-Shack theories. These new developments simplify the analysis and understanding of nonintuitive scattering behavior from rough surfaces illuminated at arbitrary incident angles.

Approach to investigating the spherical aberration variation with the object position in an aplanatic system.

In a general optical system, spherical aberration will arise when the on-axis position of an object is changed from its optimum position to another point. Induced spherical aberration can be used to compensate the aberration caused by inserting or removing a medium plate with any thickness that has a refractive index that differs from that of the original. To generate a degree of adequate aberration to balance the aberration from a thin layer, it is necessary to estimate the amount of arising aberration correctly when a point object deviates from its aberration-free position. We analytically induce the exact form of an arising spherical aberration with an on-axis object position for general optical systems that satisfy the Abbe sine condition and express a fourth-order approximation of that form using simple parameters that are conventionally used for the aberration of a thin lens. To verify the correctness of the proposed formula, a comparison between this analysis and simulation results is applied to several sample optical systems using commercial lens-design software.