For large aperture telescope, we place the significance on the jitter of the wave front parameters when we make
effort to obtain better image. We investigate the power spectral density for charactering the optical jitter for large
telescope as stochastic sequence. Limited by frequency domian property, the universal used metric, and root mean square
of wave front error (RMS WFE) cannot provide adequate information .This paper provides a complete and easy-to-use
approach to the specification of mid-and-high frequency aberration of the wave front. Additionally, we apply welch
method to the calculation of the power spectral density to achieve the accuracy result without much noise involved.
Lastly, we verify this theory by the analysis of a laser system.
We investigate a new metric power spectral density (PSD),for characterizing the performance of seeing-limited large telescope such as thirty meter telescope(TMT ). As the PSD is directly related to the performance of the atmosphere which plays an important role in ground based facilities, it represents the efficiency lose due to mid and high-spatial frequency components in observing time. The metric also properly counts for the optic error of the mirror itself such as the deviations from a perfect surface, and metrology measurement errors .The metric can multiply all the errors which differentiates from the traditional ones, such as RMS. We also numerically confirm this feature for Karman model atmosphere error multiplied with the sample of our vendor and the TMT M3.Additonaly, we discuss other pertinent feature of the PSD, including its relationship to Zernike aberration ,and RMS of wave front errors.
With the aperture of large ground-based telescopes increasing, thermal issues appear more evidently. As a relatively large thermal expansion coefficient SiC (about 2.5x10-6 /K), it makes large aperture SiC lightweight primary mirror more sensitive to temperature gradient. Firstly, discuss thermal issue of the mirror seeing induced by the temperature difference between the mirror surface and ambient theoretically. Then analyze the mirror surface deformation under seven different steady-state temperature fields with a unit temperature load. A uniform axial gradient can cause a mirror surface deflection RMS which can reach 438.4 nm. According to the simulation results, it shows that the primary is most sensitive to a uniform axial gradient and least to uniform change. Lastly, the parameter of thermal control is determined through the above analysis with the error budget to get a better image quality.