Hyperion is a far-UV mission that investigates the birth clouds of stars using a 40 cm aperture telescope feeding an imaging long-slit spectrometer. The science requirements of the mission dictate that the spectrometer covers 140.5- 164.5 nm spectral range with resolution greater than 30,000. We employ smart and efficient design to create a longslit, cross dispersed, echelle spectrometer that utilizes a two-mirror freeform imaging optics. Echelle spectra for n = - 19, -18, and -17 over a 10 arcmin × 2.5 arcsec (length × width) FFOV are imaged onto the focal plane. We simulate the optical performance and the expected spectral efficiency.
Accurate system calibration remains an area of active improvement in deflectometry. Since deflectometry requires the geometry information of all participating hardware to be well known, miscalibration can mar the accuracy of surface reconstruction especially in lower order shapes. To uphold reconstruction fidelity, extra measuring instruments (i.e. coordinate measuring machines, laser trackers, metering rods) or reference features (i.e. fiducial points or reference mirror) to find out the positions of a camera, a screen, and a unit under test are used. These methods provide reliable calibration but are resource-intensive. In this paper, we introduce an alignment algorithm to calibrate the geometry of a deflectometry configuration. We leverage the concept of alignment algorithm which uses a sensitivity model. With the aid of ray tracing simulation, the relationship between camera pixels and screen pixels of a deflectometer is quantitatively established. This pixel-to-pixel relationship enables us to generate computational imaging of screen and characterize the tendency of misalignments of the deflectometer. On top of that, we can calculate and make multiplexed patterns of screen which highlight the effect of misalignments. We set specific indices and corresponding screen patterns for each alignment parameters to build the sensitivity model. The initial simulation result shows that the algorithm can estimate misalignment status. We believe that this algorithm can be an alternative and efficient calibration process for the deflectometry system, especially when the usage of extra measuring devices is limited.
We introduce the design of a highly compact, non-planar illumination source for deflectometry. The source emits uniform and Lambertian light from a curved area resembling the inner bore of a cylinder. When equipped with motion hardware, the ring source behaves like a spatially modulated screen with a pixel pitch comparable to that of a typical LCD monitor. If this source, a detector, and test optic are coaxially aligned, then on-axis deflectometry measurements are possible for axicons and centrally obscured, convex optics. This paper highlights the illumination design behind a cylindrical ring source and its implementation as a prototype in the visible spectrum.
Reconfigurable freeform optical systems enable greatly enhanced imaging and focusing performance within nonsymmetric, compact, and ergonomic form factors. In this paper, several improvements are presented for the design, test, and data analysis with these systems. Specific improvements include definition of a modal G and C vector basis set based on Chebyshev polynomials for the design and analysis of non-circular optical systems. This framework is then incorporated into a parametric optimization process and tested with the Tomographic Ionized-carbon Mapping Experiment (TIME), a reconfigurable optical system. Beyond design, a reconfigurable deflectometry system enhances metrology to measure a fast, f/1.26 convex optic as well as an Alvarez lens. Further improvements in an infrared deflectometry system show accuracy around λ/10 of the notoriously difficult low-order power. Working together, the mathematical vector polynomial set, the programmatic optical design approach, and various deflectometry-based optical testing technologies enable more flexible and optimal utilization of freeform optical components and design configurations.
The LUCI (LBT Utility Camera in the Infrared) instruments are a pair of near infrared (NIR) imagers and spectrographs for the Large Binocular Telescope (LBT) that include a set of cryogenic exchangeable focal plane masks. Although LUCI covers the NIR zJHK bands at different resolutions with existing gratings, it is not currently possible to get zJHK in a single exposure with a single LUCI which is required for some planetary science programs. To produce a simultaneous zJHK spectrum with a single LUCI, we designed a system consisting of small and simple optical elements to fit within the limited space in the focal plane mask frame to cross-disperse fixed short slits. This system, called MOBIUS (Mask-Oriented Breadboard Implementation for Unscrambling Spectra), consists of a double-folding mirror, a collimating spherical mirror with 180 mm radius of curvature, and a dispersing prism with the rear surface mirror-coated. MOBIUS disperses the input slit perpendicular to the dispersion direction of the gratings in LUCI. The resulting order separation is at least ∼2.7 arcsecond, allowing a slit length of up to ∼2.3 arcsec without mixing orders at the LUCI image plane. Since MOBIUS would be introduced into the existing light path via the exchangeable slit mask mechanism, no modification to the current LUCI instrument is needed. Eventually, binocular observations combining one of the Multi-Object Double Spectrographs (MODS) with LUCI+MOBIUS at the LBT will provide simultaneous coverage from 0.3 to 2.4 μm for studies of asteroids and other faint solar system bodies.
In this study, we performed alignment state estimation simulations and compared the performance of two Computer Aided Alignment (hereafter CAA) algorithms i.e. ‘Merit Function Regression (MFR)’ and ‘Multiple Design Configuration Optimization (MDCO)’ for a TMA optical system. The former minimizes the merit function using multi-field wavefront error measurements from single configuration, while the latter minimizes the merit function using single-field measured wavefront error from multiple configurations. The optical system used is an unobscured three-mirror anastigmat (TMA) optical system of 70mm in diameter, and F/5.0. It is designed for an unmanned aerial vehicle for coastal water remote sensing. The TMA consists of two aspherical mirrors, a spherical mirror and a flat folding mirror. Based on the sensitivity analysis, we set the tilt x, y of tertiary mirror as a compensator, and not considered decenter of tertiary mirror because of its spherical characteristic. For the simulation, we introduced Gaussian distribution of initial misalignment to M3. It has the mean value of zero and standard deviation of 0.5 mrad. The initial simulation result of alignment state estimation shows that both algorithms can meet the alignment requirement, λ/10 RMS WFE at 633nm. However, when we includes measurement noise, the simulation result of MFR shows greater standard deviation in RMS WFE than that of MDCO. As for the measurement, the MDCO requires single on-axis field while the MFR requires multiple fields, we concluded that the MDCO is more practical method to align the off-axis TMA optics than MFR.
The design and performance analysis of a new sensor is introduced which is on board a small unmanned aerial vehicle (UAV) for coastal water remote sensing. The top level requirements of sensor are to have at least 4cm spatial resolution at 500m operating height, and 4° field of view (FOV) and 100 signal-to-noise ratio (SNR) value at 660nm. We determined the design requirements that its entrance pupil diameter is 70mm, and F-ratio is 5.0 as an optical design requirement. The three-mirror system is designed including aspheric primary and secondary mirrors, which optical performance are 1/15 λRMS wavefront error and 0.75 MTF value at 660nm. Considering the manufacturing and assembling phase, we performed the sensitivity, tolerance, and stray-light analysis. From these analysis we confirmed this optical system, which is having 4cm spatial resolution at 500m operating height, will be applied with remote sensing researches.