Recent decades have seen increased interest in Cislunar operations. To ensure the safety of flight and peace of operations in the Cislunar domain, a capability to provide current and predictive knowledge of resident space objects in the domain is required, which, in turn, necessitates a dedicated space situational awareness (SSA) system. However, SSA in the Cislunar domain is notoriously difficult to achieve due to the inherently large volume and the chaotic nature of orbits in the regime. These characteristics produce challenges in establishing persistent monitoring and limit predictive capabilities. To address these challenges, this study detailed a trade space for achieving effective Cislunar SSA (CSSA) by leveraging improved capabilities offered through very large (5-10x the size of currently available space-based apertures) radio frequency and optical sensors. The approach presupposes a paradigm shift in space operations that enables on-orbit manufacturing of large, precise structures. We show that access to very large apertures enables timely, persistent, and accurate CSSA through higher signal-to-noise ratios, resolutions, and detection ranges in the operational environment that could not otherwise be achieved by leveraging a proliferated network of many smaller, conventionally sized sensors.

Acute brain injury (ABI) is a complex disease process that begins with an initial insult followed by secondary injury resulting from disturbances in cerebral physiology. In the metabolically active brain, early recognition of physiologic derangements is critical in enabling clinicians with the insight to adjust therapeutic interventions and reduce risk of ischemia and permanent injury. Current established approaches for monitoring cerebral physiology include the neurologic physical examination, traditional brain imaging such as computed tomography (CT) and magnetic resonance imaging (MRI), electroencephalography (EEG), and bedside modalities such as invasive parenchymal probes and transcranial doppler ultrasound. Diffuse optical spectroscopy (DOS), diffuse correlation spectroscopy (DCS), and optical coherence tomography (OCT) are non-invasive optical techniques that have shown promise in measuring clinically relevant changes in cerebral physiology. These new modalities may offer clinicians significant benefits as they are safe, can be utilized at the point-of-care, and provide continuous measurements. This paper reviews major causes of primary and secondary ABI encountered in neurocritical care units, conventional measures of cerebral physiology during ABI, and emerging non-invasive optical techniques that have significant potential for translation to the bedside.

Rapid sub-nanometer neuronal deformations have been shown to occur as a consequence of action potentials in vitro, allowing for optical registration of discrete axonal and synaptic depolarizations. Such optically-measured deformations are a novel signature for recording neural activity. We demonstrate this signature can be extended to in vivo measurements through recording of rapid neuronal deformations on the population level with holographic, optical phase-based recordings. Our system demonstrates, for the first time, non-invasive recordings of in vivo tissue deformation associated with population level neuronal activity, including through-skull. We confirmed this technique across a range of neural activation models, including direct epidural focal electrical stimulation, anesthetic-induced cortical deactivation, activation of primary somatosensory cortex via whisker barrel stimulation, and pharmacologically-induced seizures. Collectively, we show holographic imaging provides a pathway for high-resolution, label-free, non-invasive recording of transcranial in vivo neural activity at depth, making it highly advantageous for studying neural function and signaling.

Rapid sub-nanometer neuronal deformations have been shown to occur as a consequence of action potentials in vitro , allowing for registration of discrete axonal and synaptic depolarizations and thus providing a novel signature for recording neural activity (1–3). We demonstrate that this signature can be extended to in vivo measurements through recording of rapid neuronal deformations on the population level with optical phase-based recordings. Complicating these measurements is the optical phase noise due to microvascular flow as well as the presence of significant tissue clutter (deformation) associated with physiologic processes (e.g., heart and respiratory rate). These recordings were acquired using a full-field holographic imaging system with spatiotemporal resolutions of less than 1 ms and 0.1 mm 3 over a 3 mm diameter field of view (FOV). Our system demonstrates, for the first time, the ability to non-invasively record in vivo tissue deformation associated with population level neuronal activity. We confirmed this technique across a range of neural activation models, including direct epidural focal electrical stimulation (FES), activation of primary somatosensory cortex via whisker barrel stimulation, and pharmacologically-induced seizures. Calibrated displacement measurements of the associated tissue deformations provided additional insight into the underlying neural activation mechanisms. Collectively, we show that holographic imaging provides a pathway for high-resolution, label-free, non-invasive recording of transcranial in vivo neural activity at depth, making it highly advantageous for studying neural function and signaling.

View Video Presentation: https://doi.org/10.2514/6.2023-1118.vid Recent decades have seen increased interest in the Moon and cislunar operations. To ensure safety of flight and peace of operations in the cislunar domain, space traffic management is required, which, in turn, necessitates a dedicated space situational awareness (SSA) system. However, SSA in the cislunar domain is notoriously difficult to achieve due to the inherently large volume and the chaotic nature of orbits in the regime. These characteristics produce challenges in establishing persistent monitoring and limit predictive capabilities. To address these challenges, we detail a trade space for constructing an effective SSA architecture in the cislunar space domain through a tiered radio frequency (RF)/optical sensing architecture. Our results show that a paradigm shift in space operations that achieves on-orbit manufacturing of large precise structures from in-situ resources enables timely and persistent cislunar SSA. Such a paradigm shift removes the launch constraints imposed on sensors, allowing for the deployment of sensors that are 5-10x the size of structures currently available. We show how large, precise optical and RF apertures improve SSA architecture performance in the cislunar domain through improved signal-to-noise ratios, resolutions, and detection ranges.

Over the past 15 years, the Johns Hopkins University Applied Physics Laboratory (APL) and others have developed and demonstrated impressive capabilities and technologies in optical communications. APL has conducted experiments, performed analysis, investigated designs, developed capabilities, coded algorithms, and conducted successful demonstrations. The critical optical communications challenge remaining for APL to solve over the next two decades is not in technology development. It is in partnering with the Department of Defense and national security space communities to apply and implement these technological achievements through the systems engineering and acquisition processes. This article discusses the history of optical communications, APL's contributions in several domains, current challenges, and the way forward.

The Defense Advanced Research Projects Agency's Revolutionizing Prosthetics program demonstrated the potential for neural interface technologies, enabling patients to control and feel a prosthetic arm and hand, and even pilot an aircraft in simulation. These landmark achievements required invasive, chronically implanted penetrating electrode arrays, which are fundamentally incompatible with applications for the able-bodied warfighter or for long-term clinical applications. Noninvasive neural recording approaches have not been as effective, suffering from severe limitations in temporal and spatial resolution, signal-to-noise ratio, depth penetration, portability, and cost. To help close these gaps, researchers at the Johns Hopkins University Applied Physics Laboratory (APL) are exploring optical techniques that record correlates of neural activity through either hemodynamic signatures or neural tissue motion as represented by the fast optical signal. Although these two signatures differ in terms of spatiotemporal resolution and depth at which the neural activity is recorded, they provide a path to realizing a portable, low-cost, high-performance brain-computer interface. If successful, this work will help usher in a new era of computing at the speed of thought.

Frequency-domain (FD) fNIRS is attractive for non-invasive brain imaging because phase-sensitive detection leads to increased resolution and may exhibit improved robustness to motion artifacts. We present an FD-fNIRS system with silicon photomultiplier (SiPM) receivers, where the sensitivity and dynamic range approach those of a first-class continuous-wave (CW-) fNIRS system. This represents a significant step toward fully exploiting the phase degree of freedom provided by FD-fNIRS. The transmitter subsystem includes 32 channels and each supplies 12.5 mW of coherent light at both 690 and 852 nm. A dedicated radio circuit intensity-modulates each laser, and they are independently configured to operate at frequencies up to 400 MHz. The transmitters are on-off-keyed according to a user-specified pattern to mitigate shot noise and maximize dynamic range. The receiver subsystem also includes 32 channels. Each consists of a large-area (2.16-mm diameter), high-NA (0.66) fiber bundle, which carries light to a custom photo-receiver. A three-lens assembly enhances coupling between the fiber-bundle and the SiPM, and the SiPM (ON Semiconductor MICRORB-10020) converts the signal to the electrical domain. The electrical signal is amplified and down-converted to the audio spectrum, and a transformer balances the signal and provides galvanic isolation. Each of the 32 audio waveforms is digitized at 192 kS/s in a bank of commercial audio digitizers. Using a modulation frequency of 211 MHz, swept-power measurements demonstrate that the average noise-equivalent power of the SiPM photo-receivers is 20.5 fW per square root Hz, with about 6 decades of optical dynamic range. This work was funded by a research contract under Facebook's Sponsored Academic Research Agreement.

We present a 32-transmitter, 32-receiver dual-wavelength frequency-domain (FD) fNIRS system comprised of commercially available avalanche photodiodes, laser drivers and laser mounts. The custom frequency domain (FD) fNIRS system is used to interrogate cerebral tissue with optodes positioned at the posterior occipital region of the head. Data are collected from human subjects watching movie scenes with no sound. We applied cross-validated PCA to identify the number of dimensions retained in the neural signal recorded using FD-fNIRS for the magnitude, phase, and FD (magnitude and phase combined) components of the recorded signal. Importantly, a comparison of the cross-validation error for each signal allows us quantify the dimensionality of the linear subspace spanned by each data type. The number of principal components producing the minimum cross-validation error for the held-out test runs represents the number of orthogonal signal dimensions preserved across training and held-out test data runs. We find that the FD signal captures a higher dimensional space compared to the magnitude or phase signals in isolation. Previous theoretical and empirical work suggest that signals extracted using FD-fNIRS contain higher fidelity neural information than CW-fNIRS in isolation. The findings reported here further support this hypothesis and extend beyond the findings reported in the literature, demonstrating that a higher dimension linear subspace is covered by FD-fNIRS above and beyond the baseline signal captured using traditional CW-fNIRS, assuming other optical performance metrics such as optical dynamic range, noiseequivalent power and cross-talk are comparable. This work was funded by a research contract under Facebook’s Sponsored Academic Research Agreement.

Optical neuroimaging technologies aim to observe neural tissue structure and function by detecting changes in optical signals (scatter, absorption, etc…) that accompany a range of anatomical and functional properties of brain tissue. At present, there is a tradeoff between spatial and temporal resolution that is not currently optimized in a single imaging modality. We have developed a coherent optical imaging approach that begins to remove this trade-off and have demonstrated high spatiotemporal (<100µm and >100Hz) in-vivo recordings of neural activity over large 20mm2 areas.

his article discusses a series of optical techniques for assessing the performance of heated IR windows. The assessment considers the complete thermo-mechanical behavior as well as the boresight error and image quality of the sensor that looks through the window. The entire discussion serves as a vehicle for emphasizing the role that fundamental research plays in the everyday mission of APL. We demonstrate that research into the fundamental properties of matter not only provides insight into the behavior of the material, but often leads to the creation of secondary tools or procedures that in turn can be used to assess system performance.

Unmanned Air Vehicle (UAV) mission objectives are continuing to expand toward precision, high-resolution target tracking and engagement in complex environment. Potential applications include biochemical plume detection and Intelligence, Surveillance and Reconnaissance (ISR). A real-time, physics-based simulation of the urban wind environment has been developed and integrated with a 6DOF model of the Unicorn UAV designed by Procerus to develop design parameters for mission critical system components. The purpose of this work is to use these integrated models to determine preliminary sensor design requirements directly related to operating a UAV in the urban environment. This simulation has been used to determine requirements for a gimbal mounted target tracking instrument and an optics-based, remote wind sensor. The simulation tool can be altered to characterize sensor requirements that are dependent on interactions with the wind and physical environment. This paper will discuss the urban simulation and 6DOF model used and the integrated results, the specific need for each of the mentioned sensor systems and how the integrated simulation is used to identify critical design parameters and resulting design requirements. Preliminary results will also be presented followed by a discussion of future work.

A 91 kg (200 lb(m)) block of aluminized solid rocket propellant was burned in open air to simulate an accidental propellant fire. A suite of remote optical instruments measured the temperature and radiative properties of the plume. Solid molybdenum calorimeters provided data for heat flux estimates. Various refractory oxide and metallic witness samples placed in the fire provided temperature benchmarks and insight into how such samples may be dispersed by the fire. A thermochemical analysis assessed the overall energy balance. The results indicate that temperatures reached 3000 +/- 100 K and heat fluxes reached 200 +/- 80W/ cm(2) under the propellant, which burned for 120 s, creating a severe environment.

A semiempirical multiphonon model based on quantum-mechanical oscillators under a Morse potential is applied to the absorption coefficient of far-infrared transmitting materials. Known material properties are combined with absorption coefficient data to fit the empirical parameters of the model. This provides an accurate means of predicting the intrinsic absorption of the materials in their multiphonon regions. Extinction data are obtained by measuring material transmittances with a Fourier-transform spectrometer and comparing them with the lossless transmittances predicted by Sellmeier models. Where appropriate, scatter models are used to separate the extinction into loss due to scatter and absorption. Data and model parameters are presented for GaAs, GaP, ZnS, and ZnSe.

Conventional ultrasonic techniques have long been recognized for their usefulness in the nondestructive testing of materials and structures. These techniques, based on launching ultrasonic or high-frequency acoustic waves into a material using a coupled transducer, enable the probing of certain material properties. By inducing surface or bulk waves into a material, several material properties, such as thickness, layer structure, and elastic moduli, can be measured. In addition, the material can be checked for cracks, delamination, or changes in porosity. Thus, by launching waves into a material and detecting any corresponding acoustic wave arrivals, it is possible to determine a significant amount of information about the material under test. In contrast to conventional methods, the field of laser-based ultrasonics (LBU) allows the same information to be collected, but through noncontact methods. In this article, we highlight the use of LBU to address problems relevant to air defense, space, and biomedicine.

The optical property characterization of Spinel and AlON samples, as provided by SURMET, is presented. Several experiments are performed to characterize the optical properties of the materials. A broadband FTIR transmissometer acquired data at temperatures ranging from 298 to 800 K covering a frequency range from 1887 cm-1 to 4000 cm-1. These measurements provided information on the broadband spectral properties of the samples and the temperature dependent shift of the multiphonon band edge. Laser transmission measurements were performed at 632.8 nm and 3.39 mm to provide very accurate transmission values at the two fixed wavelengths. Finally, BSDF measurements on uneroded/eroded sample pairs were performed at 632.8 nm and 3.39 mm. These measurements indicated that the erosion process introduced to these samples would have minimal affect on the imaging performance of the windows in the mid-infrared.

The effect of different hot pressing and hot isostatic pressing (HIP) temperatures and pressures on the optical properties of spinel was studied. Extinction coefficients of spinel samples were estimated by comparing the measured transmittance with the theoretical transmittance as calculated via a Sellmeier model. Results showed that the relative size of the scattering sites was large compared with the wavelengths of light (0.35–5.5 μm). Overall, increasing HIP temperature and pressure resulted in decreasing the optical extinction. The lower of two hot pressing temperatures (1620° vs 1650°C) prior to HIPing resulted in lower scatter coefficients after HIPing; this effect was most significant in the infrared.