The study of aquatic ecosystems is an important research area addressing diverse problems such as carbon sequestration in coastal margins and wetlands, kelp and seagrass studies, coral reefs, harmful algal blooms and hypoxia, and carbon cycling in this dynamic environment. The application of an imaging spectrometer to aquatic ecosystem study is particularly challenging due to low water-leaving radiance levels adjacent to the shore region with its higher values. The Committee on Earth Observation Satellites (CEOS) has established more stringent performance standards for the visible/near infrared wavelengths than are typically available in imaging spectrometer designs. We have recently developed a compact form imaging spectrometer, the Chrisp Compact VNIR/SWIR Imaging Spectrometer (CCVIS), that facilitates their modular usage with a wide field telescope without sacrificing performance. The CCVIS design and the operational concept have predicted performance that approaches the CEOS standards. The envisioned satellite implementation requires a pitchback maneuver where the imaging of the slit projected onto the surface is slowly scanned while recording focal plane array readouts at a higher rate thereby avoiding saturation over the land surface while obtaining a high signal-to-noise ratio over the water. The effective frame rate is determined by the time it takes to scan the projected slit one ground sample distance (GSD). This approach has the added benefit of measuring a range of angles during a single GSD acquisition, providing insight into the bidirectional reflectance distribution function (BRDF).
The alignment of precision optical assemblies can be time-consuming and labor-intensive, particularly for ap- plications that need to maintain performance through harsh environments. To achieve a rugged design, op- tomechanical elements are frequently aligned and locked in place with shims that are ground and lapped to extremely tight tolerances. The grinding and lapping process can take days, weeks, or even months in select instances that require extremely tight tolerances for alignment. In this work, we present an alternative actua- tion and lock approach that can shorten alignment times without sacrificing ruggedness or alignment resolution. The faster optical alignment is achieved with an Adjustable, Re-lockable, Ruggedized, and Kinematic (ARRK) mount principle. Select experiments demonstrate the working principle of an ARRK mount, evaluate ease-of-use, and demonstrate stability through a random vibration environment. Our results suggest ARRK mounting as a promising approach for fast, robust optical mounting in applications that need to withstand vibration.
The Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) payload will be launched to the International Space Station (ISS) in 2023. ILLUMA-T is an optical communications payload that will make the ISS the first space-based user to communicate with NASA’s Laser Communications Relay Demonstration (LCRD). The system will support all-optical forward links up to 150 Mbps and return links up to 1 Gbps. The payload recently underwent system level Thermal VACuum (TVAC) functional testing at MIT Lincoln Laboratory. We present an overview of the payload’s TVAC functional tests and results.
Free-space laser communication systems are increasingly implemented on state of the art satellites for their high-speed connectivity. This work outlines a demonstration of the Modular, Agile, Scalable Optical Terminal (MAScOT) we have developed to support Low-Earth Orbit (LEO) to deep-space communication links. In LEO, the MAScOT will be implemented on the International Space Station to support the Integrated Laser Communications Relay Demonstration (LCRD) LEO User Modem and Amplifier Terminal (ILLUMA-T) program. ILLUMA-T's overarching objective is to demonstrate high bandwidth data transfer between LEO and a ground station via a geosynchronous (GEO) relay satellite. Outside of LEO, the MAScOT will be implemented on the Artemis-II mission to demonstrate high data rate optical communications to and from the moon as part of the Optical to Orion (O2O) program. Both missions leverage the same modular architecture despite varying structural, thermal, and optical requirements. To achieve sufficient performance, the terminal relies on a nested tracking loop to realize sub-arcsecond pointing across a ±120 ° elevation and ±175° azimuth field of regard.
It is known that far-field scattered light requires a priori sample information in order to reconstruct nm-scale information such as is required in semiconductor metrology. We describe an approach to scatterometry that uses unconventional polarization states in the pupil of a high NA objective lens. We call this focused beam scatterometry; we will discuss the sensitivity limits to this approach and how it relates to micro-ellipsometry as well as low-NA scatterometry.
Point spread function engineering is usually accomplished by controlling the amplitude, phase and/or polarization of the pupil fields. We analyze and test an optical design for full amplitude, phase, and polarization control of the pupil fields using a single spatial light modulator. In our scheme, the beam is spatially split into four components whose relative phases provide the four degrees of freedom necessary for amplitude, phase, and polarization control.
Optomechanical design considerations are presented in the development of a fiber-delivered three degree-offreedom displacement measuring interferometer. The tool can be used to simultaneously calibrate the linear motion and rotational errors of a translating stage using a single measurement beam incident on a plane mirror target. This novel interferometer incorporates a quadrant photodiode to measure four spatially separated interference signals all within a single optical interference beam, otherwise known as differential wavefront sensing. In post processing, a weighted phase average is created over symmetrically adjacent pairings of detector elements to decouple and measure displacement and changes in pitch and yaw. Design considerations include a custom displacement interferometer architecture, mechanical analyses and qualification testing of a working prototype. This interferometer has the potential for providing multi-DOF calibrations for precision motion stages.
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