Segmented mirrors are commonly used to construct large-aperture telescopes. We present a methodology for structural analysis and experimental results of an adjustment of a mm- to far-IR range (10 mm to 70  μm) segmented mirror panel to correct its deviation from an optimum paraboloid of rotation. The panel is made of high-modulus carbon fiber–reinforced plastic and has a shape of a 15-deg sector with a 1207  ×  390  mm² reflecting surface area. A system of mechanically operated adjusters for correcting large-scale surface deformations is described. We used our original method to correct fabrication errors and improved the surface shape accuracy from 23.8 to 4.5  μm (RMS values). The method is based on distance-to-target-surface minimization using vector influence functions and arbitrary movements. The results of the long-term panel shape stability monitoring and the effect of cooling the panel down to 77 K are also presented.

The thermal and mechanical stabilization of the focal plane assembly (FPA) naturally has a magnificent impact on the performance of space camera. Thermal and mechanical features of the proposed FPA are described first. Special attention is paid to the thermo-structure design of the FPA. Then the fitting methods based on singular value decomposition and least square are proposed to use the finite-element analysis results to predict the relative position changes between charge coupled devices under thermal and mechanical load cases. A comprehensive finite-element model of the FPA has been built, and the alignment errors, which were induced thermal and gravity loads, are predicted based on the proposed fitting method. To further prove that the design of FPA meets the mechanical and thermal stability requirements, an optical bench was developed. Meanwhile thermal cycling and vibration test of the three FPAs were performed; the alignment error measurements of the FPAs after each test were also performed. Both the simulation and tests show a good stability of the FPA design under operational and test environments.

Juno is a spacecraft in polar orbit around Jupiter, and one of its objectives is to explore the Jovian magnetosphere. Charged particles trapped along the Jovian magnetic field lines may generate auroral emission. The Juno magnetospheric payload is designed to measure the charged particle distributions in the Jovian magnetosphere while remote sensing the related UV-auroral emissions. The ultraviolet spectrograph on Juno (Juno-UVS) is a photon-counting imaging spectrograph designed to observe Jupiter’s prominent far-UV auroral emissions in the 68 to 210 nm spectral range. This work presents an improvement on the wavelength and radiometric calibration of Juno-UVS. Ground calibration measurements were reanalyzed by expanding the spectral database ultimately used to produce the instrument spectral pixel size map. This significantly improves the wavelength assignation, up to 4 nm at the longer wavelengths, compared with the previous calibration. Dedicated Juno-UVS observation sequences were made to evaluate the slit-dependent radiometric calibration, which was revised accordingly. This work highlights a slight slit-dependent variation in the radiometric calibration. An additional radiometric correction was established at wavelengths greater than 160 nm using some of UVS’s brightest recorded stellar spectra.

The experiment for cryogenic large-aperture intensity mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation in windows from the present to z  =  3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission of singly ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering 420 to 540 GHz with spectral resolving power R  =  512 and angular resolution ≈4  arc min. The spectral resolving power and cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere. EXCLAIM will survey 305  deg² in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as tracers of molecular gas. We summarize the design phase of the mission.

We present results on the laboratory characterization of the grating vector apodizing phase plate (gvAPP) coronagraph that will be included in the upcoming instrument enhanced resolution imager and spectrograph (ERIS) at the VLT. ERIS will include a 1 to 5  μm adaptive-optics-fed imager, NIX, that will greatly improve the capability of the VLT to perform high-contrast imaging of exoplanets especially in the 3 to 5  μm wavelength range. The gvAPP, one of the coronagraphs in the NIX suite, is a pupil plane coronagraph that uses a thin film of patterned liquid crystals to create two images of a star with a D-shaped dark hole on either side. The gvAPP is manufactured using an innovative direct-write system that produces precise patterns of liquid crystals. We utilized the upgraded infrared cryogenic test bench run by the Exoplanets and Habitability Group at ETH Zurich to measure the morphology of the gvAPP PSF and to test the accuracy of the liquid crystal manufacturing technique in the lab for the first time at contrast levels of ∼10^−  5. We find that the gvAPP can reach raw contrasts below ∼10^−  5 between ∼10 and 13  λ  /  D. This contrast upper limit translates to a writing accuracy of the orientation of the liquid crystal’s fast axis of better than 0.3 deg for the spatial frequencies corresponding to those separations. This is a sufficient accuracy such that the gvAPP will not be the limiting factor in achieving the required contrasts to image exoplanets.

The REgolith X-ray Imaging Spectrometer (REXIS) is a soft x-ray spectrometer and the student collaboration instrument aboard NASA’s OSIRIS-REx asteroid sample return mission. REXIS utilizes MIT Lincoln Laboratory CCID-41 x-ray detectors coated with a directly deposited optical blocking filter (OBF) with a thickness of 320 nm. The aluminum coating, developed at MIT Lincoln Laboratory, is designed to block visible light from the detector, to maintain high sensitivity to soft x-rays in the presence of reflected sunlight from the surface of the target asteroid Bennu. The scientific objective for the REXIS instrument is to measure the stimulated x-ray flux fluoresced from Bennu to discern elemental abundances present on the asteroid’s surface. The coating technique applied for blocking visible light had not previously been used on the CCD-41s in an extended space flight mission. The performance of the OBF on the flight detectors was not characterized before and after environmental stress testing. Therefore, to mature the OBF to technology readiness level (TRL) 6, the flight spare detectors were tested while the instrument was on the way to the asteroid. The flight spare hardware underwent vibration and thermal environmental stress testing to test the durability and effectiveness of the OBF. This testing informed our expectations of the in-flight OBF once it reached the asteroid and helped mature the TRL level of this directly deposited OBF. We discuss the setup and results of those tests and address the performance of the flight OBF at the asteroid. We conclude that depositing an aluminum OBF onto the surface of a charge-coupled device is able to withstand stresses of launch and an extended life-mission in interplanetary space.

Consumer-level digital single-lens reflex (DSLR) cameras are typically not used in professional astronomy because of the systematic errors present in the data as a result of the strong intra- and interpixel variations associated with each of the three different colors (RGB) of the Bayer color filter array. Nevertheless, because the cost of DSLRs compared with traditional astronomical CCDs is so much lower, they represent a potentially underexplored area of scientific quality astronomical imaging, especially in the area of wide-field transient surveys. We demonstrate an algorithm that can achieve   ≈  1  %   level photometry in each of the RGB color channels from a stellar source and discuss the application of this algorithm to a ground-based transiting exoplanet survey. The algorithm primarily takes advantage of the large number of stellar sources available for statistical averaging within a single image, using a “lucky point-spread function” approach to identify sources in the image that exhibit systematic errors consistent with a chosen target from the same image. The selection of the appropriate“lucky” reference stars is accomplished through a comparison of the stellar image morphology as it appears on the Bayer array and the reference stars. These references are linearly combined to form a synthetic comparison star that can be used for differential photometry with the target. One key to the algorithm is that all data are retained at the individual pixel-level until the final differential comparison, which helps to alleviate systematic effects that might otherwise cancel each other out during the flux-summing process. We demonstrate the algorithm on HD 339461, a m_V  =  8.93 G0-type star on which we achieve single-percent level photometry that approaches the fundamental noise floor possible from a single camera.

Electro-optical testing and characterization of the Vera C. Rubin Observatory Legacy Survey of Space and Time Camera has shown that the focal plane charge-coupled devices developed by Imaging Technology Laboratory exhibit serial deferred charge signal in excess of the expected proportional deferred charge loss from global charge transfer inefficiency. We model the additional deferred charge as resulting from localized charge trapping in the serial register and from a signal-dependent electronic offset effect. A physically motivated forward deferred charge simulation algorithm and a reverse deferred charge correction algorithm were developed in order to correct for deferred charge during data reduction and reduce the possible impacts on Rubin Observatory project science goals. We apply the correction algorithm to calibration data and demonstrate the ability to reduce deferred charge signal measured in the overscan pixel regions and remove the serial pixel correlations resulting from the redistribution of charge between pixel neighbors during readout.

We develop a photon energy measurement scheme for single photon counting Microwave Kinetic Inductance Detectors (MKIDs) that uses principal component analysis (PCA) to measure the energy of an incident photon from the signal (“photon pulse”) generated by the detector. PCA can be used to characterize a photon pulse using an arbitrarily large number of features and therefore PCA-based energy measurement does not rely on the assumption of an energy-independent pulse shape that is made in standard filtering techniques. A PCA-based method for energy measurement is especially useful in applications where the detector is operating near its saturation energy and pulse shape varies strongly with photon energy. It has been shown previously that PCA using two principal components can be used as an energy-measurement scheme. We extend upon these ideas and develop a method for measuring the energies of photons by characterizing their pulse shapes using any number of principal components and any number of calibration energies. Applying this technique with 50 principal components, we show improvements to a previously-reported energy resolution for Thermal Kinetic Inductance Detectors (TKIDs) from 75 eV to 43 eV at 5.9 keV. We also apply this technique with 50 principal components to data from an optical to near-IR MKID and achieve energy resolutions that are consistent with the best results from existing analysis techniques.

A state-of-the-art compact Low-Energy X-ray Reflectometer is in operation at DTU Space and is used to characterize x-ray coatings for the optics of future spaceborne and ground-based telescopes. The reflectometer is housed in a vacuum chamber and operates at 1.487 keV, complimenting an existing 8.048 keV reflectometer. With a microfocus source and plane-parabolic Kirkpatrick–Baez mirrors, the 0.5-mm wide beam is collimated to <0.75 arcmin. An actively cooled 2D CCD yields sample alignment precision of 26  μm in linear position and 0.18 arcmin in angle. A multilayer monochromator provides a peak reflectance of 43.5% and beam purity > 99  %  . The reflectometer has a 2θ range of 0 deg to 35 deg and dynamic range up to eight orders of magnitude. Techniques are demonstrated to investigate the sample surface morphology and we show the system’s capability to detect the presence of atmospheric contaminants on coated mirrors.

Astronomical instruments greatly improve wavelength multiplexing capabilities by using beam splitters. In the case of the 4-m National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) solar telescope, over 70 W of optical power is distributed simultaneously to four instruments, each with multiple cameras. Many DKIST observing cases require simultaneous observations of many narrow bandpasses combined with an adaptive optics system. The facility uses five dichroic optical stations to allow at least 11 cameras and two wavefront sensors to simultaneously observe ultraviolet to infrared wavelengths with flexible reconfiguration. The DKIST dichroics required substantial development to achieve very tight specifications over very large apertures of 290 mm diameter. Coating spectral variation occurs over <1  nm wavelength, comparable with instrument bandpasses. We measure retardance spectral variation of up to a full wave and diattenuation varying over ±10  %   per nm. Spatial variation of Mueller matrix elements for coatings in both transmission and reflection requires careful metrology. We demonstrate coatings from multiple vendors exhibit this behavior. We show achievement of 5-nm root mean square (RMS) reflected wavefront and 24-nm RMS power with coatings over 8  μm thick. We show mild impacts of depolarization and spectral variation of polarization on modulation efficiency caused by the dichroic coatings. We show an end-to-end system polarization model for the visible spectropolarimeter instrument, including the dichroics, grating, analyzer, and all coated optics. We show detailed performance for all DKIST dichroics for community use in planning future observations.

The Giant Segmented Mirror Telescopes (GSMTs) including the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT), and the European Extremely Large Telescope (E-ELT), all have extreme adaptive optics (ExAO) instruments planned that will use pyramid wavefront sensors (PWFS). The ExAO instruments all have common features: a high-actuator-count deformable mirror running at extreme speeds (>1  kHz); a high-performance wavefront sensor (WFS); and a high-contrast coronagraph. ExAO WFS performance is currently limited by the need for high spatial sampling of the wavefront which requires large detectors. For ExAO instruments for the next generation of telescopes, alternative architectures of WFS are under consideration because there is a trade-off between detector size, speed, and noise that reduces the performance of GSMT-ExAO wavefront control. One option under consideration for a GSMT-ExAO wavefront sensor is a three-sided PWFS (3PWFS). The 3PWFS creates three copies of the telescope pupil for wavefront sensing, compared to the conventional four-sided PWFS (4PWFS), which uses four pupils. The 3PWFS uses fewer detector pixels than the 4PWFS and should therefore be less sensitive to read noise. Here we develop a mathematical formalism based on the diffraction theory description of the Foucault knife-edge test that predicts the intensity pattern after the PWFS. Our formalism allows us to calculate the intensity in the pupil images formed by the PWFS in the presence of phase errors corresponding to arbitrary Fourier modes. We use these results to motivate how we process signals from a 3PWFS. We compare the raw intensity (RI) method, and derive the Slopes Maps (SM) calculation for the 3PWFS, which combines the three pupil images of the 3PWFS to obtain the X and Y slopes of the wavefront. We then use the Object Oriented MATLAB Adaptive Optics toolbox (OOMAO) to simulate an end-to-end model of an AO system using a PWFS with modulation and compare the performance of the 3PWFS to the 4PWFS. In the case of a low read noise detector, the Strehl ratios of the 3PWFS and 4PWFS are within 0.01. When we included higher read noise in the simulation, we found a Strehl ratio gain of 0.036 for the 3PWFS using RI over the 4PWFS using SM at a stellar magnitude of 10. At the same magnitude, the 4PWFS RI also outperformed the 4PWFS SM, but the gain was only 0.012 Strehl. This is significant because 4PWFS using SM is how the PWFS is conventionally used for AO wavefront sensing. We have found that the 3PWFS is a viable WFS that can fully reconstruct a wavefront and produce a stable closed-loop with correction comparable to that of a 4PWFS, with modestly better performance for high read-noise detectors.

Multi-conjugate adaptive optics (MCAO) uses two or more deformable mirrors (DMs) at conjugate altitudes approximately matched to the atmospheric turbulence layers to increase the corrected field of view. An important unresolved problem for MCAO is determining the optimal sequence of the DMs. Theoretical considerations and numerical studies suggest that ordering the DMs from lowest to highest altitude reduces the effects of scintillation, whereas on-sky experiments report that the best performance is attained with the ground-layer DM placed last. Using analytical calculations and numerical experiments with Fresnel propagation of Kolmogorov turbulence, we demonstrate that the scintillation results from spatial frequencies higher than the spatial sampling of high-altitude DMs are able to correct. Hence, the effect of scintillation is not impacted by MCAO correction regardless of the sequence of the DMs. Using end-to-end numerical simulations, we find that the dynamic misregistration between the DMs and the wavefront sensors is minimized by placing the ground-layer DM last, leading to increased loop stability and lower wavefront errors. Contrary to conventional wisdom, we recommend that the DMs be sequenced from highest to lowest altitude.

Off-axis three-mirror anastigmatic (TMA) telescopes with designed decenters and tilts, have many misalignment degrees of freedom and strong coupling between each misalignment degree of freedom. Therefore, it is difficult to establish misalignment equations only using A222 and A131 in nodal aberration theory (NAT). In addition, for off-axis TMA optical systems with designed decenters and tilts, the robustness of the existing fifth-order NAT misalignment calculation algorithm based on high-order Zernike coefficients and boresight errors decreases, so it is difficult to realize its engineering application. To solve the issue of insufficient practicality of the existing misalignment algorithm based on fifth-order NAT, a third-order NAT calculation algorithm based on quadratic aberration field decenter vectors is derived and established. Two concepts of inherent aberration field decenter vector and misalignment aberration field decenter vector are proposed. Taking an off-axis TMA optical system with 6-m focal length as the research object, simulations, and alignment verification experiments were carried out. Compared with the existing fifth-order NAT misalignment algorithm, the results show that when measurement noise is not considered, the two methods can both obtain convergent calculation results, and the average RMS wavefront errors (WFE) of the optical system are both corrected to be below 0.0574 waves. When different levels of measurement noise are introduced, the robustness of the fifth-order NAT misalignment algorithm decreases, and there are even cases where the optical system completely fails to be corrected. However, the algorithm based on quadratic aberration field decenter vectors shows better robustness. Under different levels of measurement noise, this algorithm could correct the average RMS WFE of the optical system to around 0.0574 waves.