The relationships between system transfer function and power spectral density measurements

Power spectral density (PSD) is being used to evaluate the surface finish and wavefront errors in mid-spatial frequency of optical components, but whether a PSD curve is credible or not is now a problem to be solved urgently. PSD curves measured by different instruments make an influence on the estimate of optical components. In order to solve this problem, we use system transfer function (STF) to find the relationships between different instruments and PSD measurements. A mathematical model of STF and PSD measurement is established to stimulate and find the floor level of STF to get a credible PSD. The experiment results that the instruments with STF at least 60% can be used in mid-spatial frequency measurements.