Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences

COLLEGE OF ENGINEERING

UC Berkeley

Vector Scattering Analysis of TPF Coronagraph Pupil Masks

Daniel Peter Ceperley

EECS Department
University of California, Berkeley
Technical Report No. UCB/EECS-2005-29
December 19, 2005

http://www.eecs.berkeley.edu/Pubs/TechRpts/2005/EECS-2005-29.pdf

The finite-difference time-domain (FDTD) method is used to simulate the scattering from prototypical pupil mask cross-section geometries in 2D for the Terrestrial Planet Finder Coronagraph (TPF-C) and to quantify the differences from the normally assumed ideal on-off behavior. Physical effects (such as real metals, thick masks, sidewall geometry, and polarization) are considered along with numerical effects (such as numerical dispersion and source haze) of the FDTD method. The physical studies have shown that undercut angle and mask material are the two most important design choices when moving a shaped pupil mask from theory to implementation. The accuracy in magnitude and phase required for modeling a chronograph system to achieve the 10^10 star-light rejection level over the 500-800nm wavelength range is extremely demanding and previously inconsequential numerical errors may be of the same order of magnitude as the physical phenomena under study. Using a cell density of 53cells/wavelength reduces the numerical dispersion to 0.04% and results in PML reflections and source haze three order of magnitude in intensity smaller than the physical effects under study. Effects of thick masks, real materials, and various cross-section geometries on the transmission of pupil-plane masks are illustrated. The differences between the designed opening widths and the electromagnetic widths are examined at the reference plane of the mask opening. Undercutting the edge shape of Cr masks improves the effective opening width to within lambda/5 of the actual opening but, for metals in general, TE and TM polarizations require opposite compensations. Undercutting and doping (or coating with a thin layer of metal) Silicon reduces the difference between the designed and effective opening widths from multiple wavelengths down to less than lambda/10.

Advisor: Andrew R. Neureuther


BibTeX citation:

@mastersthesis{Ceperley:EECS-2005-29,
    Author = {Ceperley, Daniel Peter},
    Title = {Vector Scattering Analysis of TPF Coronagraph Pupil Masks},
    School = {EECS Department, University of California, Berkeley},
    Year = {2005},
    Month = {Dec},
    URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/2005/EECS-2005-29.html},
    Number = {UCB/EECS-2005-29},
    Abstract = {The finite-difference time-domain (FDTD) method is used to simulate the scattering from prototypical pupil mask cross-section geometries in 2D for the Terrestrial Planet Finder Coronagraph (TPF-C) and to quantify the differences from the normally assumed ideal on-off behavior. Physical effects (such as real metals, thick masks, sidewall geometry, and polarization) are considered along with numerical effects (such as numerical dispersion and source haze) of the FDTD method. The physical studies have shown that undercut angle and mask material are the two most important design choices when moving a shaped pupil mask from theory to implementation.

The accuracy in magnitude and phase required for modeling a chronograph system to achieve the 10^10 star-light rejection level over the 500-800nm wavelength range is extremely demanding and previously inconsequential numerical errors may be of the same order of magnitude as the physical phenomena under study. Using a cell density of 53cells/wavelength reduces the numerical dispersion to 0.04% and results in PML reflections and source haze three order of magnitude in intensity smaller than the physical effects under study. Effects of thick masks, real materials, and various cross-section geometries on the transmission of pupil-plane masks are illustrated. The differences between the designed opening widths and the electromagnetic widths are examined at the reference plane of the mask opening. Undercutting the edge shape of Cr masks improves the effective opening width to within lambda/5 of the actual opening but, for metals in general, TE and TM polarizations require opposite compensations.  Undercutting and doping (or coating with a thin layer of metal) Silicon reduces the difference between the designed and effective opening widths from multiple wavelengths down to less than lambda/10.}
}

EndNote citation:

%0 Thesis
%A Ceperley, Daniel Peter
%T Vector Scattering Analysis of TPF Coronagraph Pupil Masks
%I EECS Department, University of California, Berkeley
%D 2005
%8 December 19
%@ UCB/EECS-2005-29
%U http://www.eecs.berkeley.edu/Pubs/TechRpts/2005/EECS-2005-29.html
%F Ceperley:EECS-2005-29