Planet Formation research is blooming in an era where we are moving from speaking about “protoplanetary disks” to “planet forming disks” (1). However, this transition is still motivated by indirect (but convincing) hints. Up to date, the direct detection of planets “in the making” remains elusive with the remarkable exception of PDS 70 b and c (2; 3; 4). The scarcity of detections is attributable to technical challenges, and even for the rare jewels that we can detect, characterization is unachievable. The next step in this direction demands from near to mid-infrared interferometry to jump from ∼100 m baselines to ∼1 km, and from very few telescopes to 20 or more (PFI like concepts, (5)). This transition needs for more affordable near to mid-infrared telescopes to be designed. Since the driving cost for such telescopes resides on the primary mirror, in particular scaling with its diameter and weight, our approach to tackle this problem relies on the production of low-cost light mirrors
In this paper, we develop an identification technique based on continuous-time Kautz basis functions and Maximum Likelihood estimation from discrete-time data to obtain a continuous-time model of a laboratory adaptive optics system. We illustrate the proposed identification method using synthetic data and experimental data of a laboratory adaptive optics setup. Finally we utilize the estimated model to develop a Model Predictive Control strategy that considers the deformable mirror actuation constraints. We illustrate the benefits of the model predictive control strategy via simulations and compare it against the classical Proportional-Integral controller.
The surface quality of replicated CFRP mirrors is ideally expected to be as good as the mandrel from which they are manufactured. In practice, a number of factors produce surface imperfections in the final mirrors at different scales. To understand where this errors come from, and develop improvements to the manufacturing process accordingly, a wide range of metrology techniques and quality control methods must be adopted. Mechanical and optical instruments are employed to characterise glass mandrels and CFRP replicas at different spatial frequency ranges. Modal analysis is used to identify large scale aberrations, complemented with a spectral analysis at medium and small scales. It is seen that astigmatism is the dominant aberration in the CFRP replicas. On the medium and small scales, we have observed that fiber print-through and surface roughness can be improved significantly by an extra resin layer over the replica's surface, but still some residual irregularities are present.
In the era of high-angular resolution astronomical instrumentation, where long and very long baseline interferometers (constituted by many, ∼20 or more, telescopes) are expected to work not only in the millimeter and submillimeter domain, but also at near and mid infrared wavelengths (experiments such as the Planet Formation Imager, PFI, see Monnier et al. 2018 for an update on its design); any promising strategy to alleviate the costs of the individual telescopes involved needs to be explored. In a recent collaboration between engineers, experimental physicists and astronomers in Valparaiso, Chile, we are gaining expertise in the production of light carbon fiber polymer reinforced mirrors. The working principle consists in replicating a glass, or other substrate, mandrel surface with the mirrored adequate curvature, surface characteristics and general shape. Once the carbon fiber base has hardened, previous studies have shown that it can be coated (aluminum) using standard coating processes/techniques designed for glass-based mirrors. The resulting surface quality is highly dependent on the temperature and humidity control among other variables. Current efforts are focused on improving the smoothness of the resulting surfaces to meet near/mid infrared specifications, overcoming, among others, possible deteriorations derived from the replication process. In a second step, at the validation and quality control stage, the mirrors are characterized using simple/traditional tools like spherometers (down to micron precision), but also an optical bench with a Shack-Hartman wavefront sensor. This research line is developed in parallel with a more classical glass-based approach, and in both cases we are prototyping at the small scale of few tens of cms. We here present our progress on these two approaches.
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