Intensity interferometry (II) is an alternate form of creating images of distant objects. It is significantly less sensitive to atmospheric distortions and aberrations of telescope surfaces than conventional amplitude-based imaging. The deficiencies of II can be overcome as photodetectors’ read-out rates are becoming faster and computers more powerful. In recognition of the possibility of very large space-based imaging systems, this paper investigates how the deformation of a large, thin optical surface would influence the accuracy of II. Based on the theoretical foundation of II, an optical ray-tracing algorithm was used to examine how the statistics of a photon stream changes from the source to the detector. Ray-tracing and finite element analyses of the structure were thereafter integrated to quantify how the correlation of the intensity field changes as the reflective structure deforms. Varying the positions of the detector from the focal plane and the surface profile of the mirror provided an understanding and quantification of how the various scenarios affect the statistics of the detected light and the correlation measurement. This research and analysis provide the means to quantify how structural perturbations of focal mirrors affect the statistics of photon stream detections inherent in II instrumentation.
Using a single focal parabolic reflector of an intensity interferometer(II) system is simulated. The extent that focal properties amongst a parabolic reflector can change the statistics of the light at a detector is analyzed. Recent technological advances have increased the speed and sensitivity of photon detectors, developed large scale precision optics, and incorporated multi-spectral imaging techniques which have led the way to reexamine the usefulness of II for scientific measurements. A ray tracing algorithm is used to examine how the statistical variations of simulated monochromatic stellar light changes from the source to the detector. Changing the position of the detector from the focal plane and changing the surface profile of the mirror develops a metric to understand how the varying scenario’s affects the statistics of the detected light. Photon streams are evaluated for light distribution, time of flight, and statistical changes at a detector. This research and analysis is used as a tool to develop a metric to quantify how structural perturbation effect the statistics of photon stream detections inherent in II instrumentation and science.
This paper presents the results of an experimental study to establish process parameters for repeatable, high quality ablated features in ferrous substrates using a Ti:sapphire femtosecond laser system. Initial trials with stainless steel substrates were conducted in ambient atmospheric conditions. Laser power and exposure parameters were varied, in addition to the angle of the substrate relative to the beam. Ablated holes were sectioned, and examined. Data was reduced according to the Taguchi/ANOVA method. The optimal process parameter set minimized the figures of merit for quality or accuracy of the ablated hole. In trials using pulsed ablations, high accuracy holes were associated with laser power greater than 600 mW, substrate angles of 30-45 degrees, and 1000 pulses. In the dwell experiments, high accuracy holes were achieved with a similar power level, and a 1-second dwell time. In contrast to the pulse results, a shallow substrate angle (30 degrees or less) yielded favorable results. In subsequent trials, kovar substrates were processed in a vacuum at constant fluence with a 1-second dwell time. A localized flow of nitrogen removed ablation products. Results were compared to those of the initial trial, leading to significant observations regarding the use of vacuum and secondary process gas.