title: Approximation of normalized point source sensitivity using power spectral density and slopes of wavefront aberration.
abstract: We have investigated two approximation methods for estimating the normalized point source sensitivity (PSSN), which is a recently developed optical performance metric for telescopes. One is an approximation based on the power spectral density (PSD) of the wavefront error. The other is the root-square-sum of the wavefront slope. We call these approximations β approximation and SlopeRMS approximation, respectively. Our analysis shows that for the Thirty Meter Telescope (TMT), the uncertainty of the β approximation is less than 1×10(-3) if the PSSN is better than 0.95, assuming the input PSD estimation is accurate. In addition, we find that the SlopeRMS approximation is a simple method for estimating the worst-case PSSN value in the specific situation when the PSSN is dominated by low-frequency aberrations. Therefore, the SlopeRMS approximation is expected to be useful for specifying a mirror surface for mirror vendors. Accordingly, TMT has a plan to adopt the SlopeRMS approximation for its M2 and M3 polishing specification.
authors.affiliation: Jet Propulsion Laboratory, Pasadena, California 91109, USA. Byoung-Joon.Seo@jpl.nasa.gov
authors.forename: Byoung-Joon
authors.initials: BJ
authors.lastname: Seo
authors.forename: Carl
authors.initials: C
authors.lastname: Nissly
authors.forename: Mitchell
authors.initials: M
authors.lastname: Troy
authors.forename: George
authors.initials: G
authors.lastname: Angeli
authors.forename: Virginia
authors.initials: V
authors.lastname: Ford
authors.forename: Larry
authors.initials: L
authors.lastname: Stepp
authors.forename: Eric
authors.initials: E
authors.lastname: Williams