We will present the status of the Navy Precision Optical Interferometer. We will discuss upgrades that occurred over the course of the last couple of years, their related scientific achievements, ongoing and future work. We will discuss the improvements done to the infrastructure of the site, the return to observations with 6 telescopes simultaneously and the results of these observations. We will discuss the deployment of new capabilities, such as an infrared beam combiner, siderostat controllers and a new angle tracker. We will also present the deployment of the Amon Hen hypertelescope experiment and changes done to the inner room in order to accommodate the use of both systems without the need of large rearrangements of the optics.
We have been progressing on our comprehensive program of improving high-resolution imaging at the Navy Precision Optical Interferometer (NPOI) hosted at Lowell Observatory’s Anderson Mesa site, for the purpose of spatially resolved observations of faint objects at scales down to less than 1 milliarcsecond. The ‘PALANTIR’ upgrade of NPOI has commenced with individually operating 1 meter PlaneWave PW1000 telescopes at the site, with integration of those telescopes into the array with interferometric operations expected in the near-term. These telescopes are housed in mobile domes for rapid relocation around the array, and are being augmented with adaptive optics. Another notable recent milestone has been the re-activation of full six-way on-sky operations with siderostat feeds during the summer of 2021. Additionally, our ‘NPOI Plus-Up’ plan will implement sweeping infrastructure updates, improving and streamlining its operations. Upcoming Plus-Up work taking place over the next few years includes expansion of the operating infrastructure to the array’s longest physical baselines at 432 meters, adding a near-infrared beam combiner, rehabilitation of the VISION visible combiner, modernization of the fast delay line control system, and implementation of the long delay lines in the framework of a beam train auto-aligner.
We have been pursuing a comprehensive program of improving high-resolution imaging at the Navy Precision Optical Interferometer (NPOI) hosted at Lowell Observatory’s Anderson Mesa site, for the purpose of spatially resolved observations of faint objects at scales down to less than 1 milliarcsecond. This activity at NPOI is being implemented with two primary phases. First, the ‘PALANTIR’ upgrade of NPOI is augmenting the existing telescope array with three 1-meter PlaneWave PW1000 telescopes. These telescopes are housed in mobile domes for rapid relocation around the array, and are being augmented with adaptive optics. Second, we are implementing a ‘NPOI Plus-Up’ plan which is modernizing the array infrastructure and streamlining its operations. All of these activities are being carried out as our current operations are continuing.
The concavity of an initially flat wavefront typically increases after each reflection of the ten-reflection beam transport system at the Navy Precision Optical Interferometer (NPOI). Ideally, the exiting wavefront contour from the beam transport system preserves the original contour that enters. The beam transport system is common to and separate from the front-end, which includes primary light collectors such as siderostats or telescopes, and the back-end which includes major subsystems such as the optical delay lines, beam combiners and detectors. The beam transport system should have minimal influence on the interferometer. However, manufacturing tolerances and mount-induced deformations of each mirror collude to alter each reflected wavefront. All beam transport mirrors at the NPOI are slightly concave and each reflection adds to the concavity in the resultant wavefront. To improve the flatness of the resultant wavefront, we counter-deform a single mirror in the ten-reflection transport system. Previous analytical work using finite element analysis demonstrated the feasibility of this approach. In the present work, we have undertaken the task of verifying this approach experimentally. We set up a nine-reflection system of NPOI transport mirrors and measured the resultant beam wavefront contour. We applied a single actuator to the backside of one of the mirrors in the system and measured the contour of the exiting wavefront. Additionally, we compared the reduced concavity of the exiting wavefront to our finite element method results from the previous work, and excellent agreement was observed. In this paper, we describe our wavefront improvement approach, experimental method and results, and recommendations.
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