Search

Due to the low flux of exoEarths, long exposure times are required to spectrally characterize them. During these long exposures, the contrast in the dark hole will degrade as the the optical system drifts from its initial DH state. To prevent such contrast drift, a wavefront sensing and control (WFSC) algorithm running in parallel to the science acquisition can stabilize the contrast. However, pairwise probing (PWP) cannot be reused to efficiently stabilize the contrast since it relies on strong temporal modulation of the intensity in the image plane, which would interrupt the science acquisition. The use of small amplitude probes has been demonstrated but requires multiple measurements from each science sub-band to converge. Conversely, spectral linear dark field control (LDFC) takes advantage of the linear relationship between the change in intensity of the post-coronagraph out-of-band image and small changes in wavefront in the science band to preserve the DH region during science exposures. In this paper, we show experimental results that demonstrate spectral LDFC stabilizes the contrast to levels of a few $10^{-9}$ on a Lyot coronagraph testbed which is housed in a vacuum chamber. Promising results show that spectral LDFC is able to correct for disturbances that degrade the contrast by more than 100$\times$. To our knowledge, this is the first experimental demonstration of spectral LDFC and the first demonstration of spatial or spectral LDFC on a vacuum coronagraph testbed and at contrast levels less than $10^{-8}$., Comment: 14 pages, 10 figures, Techniques and Instrumentation for Detection of Exoplanets XI

Coronagraphic instruments provide a great chance of enabling high contrast spectroscopy for the pursuit of finding a habitable world. Future space telescope coronagraph instruments require high performing focal plane masks in combination with precise wavefront sensing and control techniques to achieve dark holes for planet detection. Several wavefront control algorithms have been developed in recent years that might vary in performance depending on the coronagraph they are paired with. This study compares 3 model-free and model-based algorithms when coupled with either a Vector (VVC) or a Scalar (SVC) Vortex Coronagraph mask in the same laboratory conditions: Pairwise Probing with Electric Field Conjugation, the Self-Coherent Camera with Electric Field Conjugation, and Implicit Electric Field Conjugation. We present experimental results from the In-Air Coronagraph Testbed (IACT) at JPL in narrowband and broadband light, comparing the pros and cons of each of these wavefront sensing and control algorithms with respect to their potential for future space telescopes., Comment: Conference Proceedings of SPIE: Techniques and Instrumentation for Detection of Exoplanets XI, vol. 12680 (2023)

Directly imaging Earth-sized exoplanets with a visible-light coronagraph instrument on a space telescope will require a system that can achieve $\sim10^{-10}$ raw contrast and maintain it for the duration of observations (on the order of hours or more). We are designing, manufacturing, and testing Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous wavefront sensing and control using out-of-band light to maintain high contrast in the science focal plane. Our initial design uses a tiered metallic focal plane occulter to suppress starlight in the transmitted coronagraph channel and a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing camera. The occulter design introduces a phase shift such that the reflected channel is a Zernike wavefront sensor. The dichroic coating allows higher-order wavefront errors to be detected which is especially critical for compensating for residual drifts from an actively-controlled segmented primary mirror. A second-generation design concept includes a metasurface to create polarization-dependent phase shifts in the reflected beam, which has several advantages including an extended dynamic range. We will present the focal plane mask designs, characterization, and initial testing at NASA's High Contrast Imaging Testbed (HCIT) facility., Comment: To appear in the Proceedings of the SPIE, Techniques and Instrumentation for Detection of Exoplanets XI

The unparalleled theoretical performance of an ideal vector vortex coronagraph makes it one of the most promising technologies for directly imaging exoplanets with a future, off-axis space telescope. However, the image contrast required for observing the light reflected from Earth-sized planets ($\sim10^{-10}$) has yet to be demonstrated in a laboratory setting. With recent advances in the manufacturing of liquid crystal vector vortex waveplates as well as system-level performance improvements on our testbeds, we have achieved raw contrast of 1.6$\times10^{-9}$ and 5.9$\times10^{-9}$ in 10% and 20% optical bandwidths, respectively, averaged over 3-10$\lambda/D$ separations on one side of the pseudo-star. The former represents a factor of 10 improvement over the previously reported performance. We show experimental comparisons of the contrast achieved as a function of spectral bandwidth. We provide estimates of the limiting error terms and discuss the improvements needed to close the gap in contrast performance required for future exoplanet imaging space telescopes., Comment: To appear in the Proceedings of the SPIE

Breakthrough Starshot is an international engineering project which aims to develop a spacecraft launch system capable of reaching our nearest star neighbors in under 1 human lifetime. To achieve such high-speed interstellar travel, the Starshot system plans to accelerate an ultra-lightweight nanocraft with 100 GW of radiation pressure. This laser light will come from a massive ground-based launch projector and will focus through the atmosphere onto a 4 meter wide lightsail attached to the nanocraft. With 10 minutes of continuous laser power, the force of this light can accelerate a 1g nanocraft to 20% the speed of light. Such speeds can enable travelling to our nearest star neighbor in just 20 years. For the laser to effectively focus on the nanocraft after traversing the turbulence of Earth’s atmosphere, the Starshot system will need an Adaptive Optics system to ‘pre-correct’ the beam before transmission. To measure the distorting effects of the atmosphere, an artificial beacon must be placed high in altitude near the nanocraft through its launch. Proposed is a satellite-based laser guide star (SLGS) which will be attached to the mothercraft satellite which releases the nanocraft during launch. However, the satellite’s lateral and radial motion in the sky from the nanocraft threatens to introduce angular and focal anisoplanatic errors, respectively, that would make proper adaptive correction impossible. By creating a fully parameterizable orbital simulation of the mothercraft and nanocraft’s positions relative to the launch projector, it was found that there exist orbital configurations which keep these anisoplanatic errors within reason. One such orbit has an orbital period of 4 days and an eccentricity of 0.88. Following adaptive correction, it is vital that residual wavefront error does not introduce perturbances which cause the sail to fall out of the beam. Given that the sail behaves like a particle trapped in a potential well, a statistical model was created

Breakthrough Starshot is an international engineering project which aims to develop a spacecraft launch system capable of reaching our nearest star neighbors in under 1 human lifetime. To achieve such high-speed interstellar travel, the Starshot system plans to accelerate an ultra-lightweight nanocraft with 100 GW of radiation pressure. This laser light will come from a massive ground-based launch projector and will focus through the atmosphere onto a 4 meter wide lightsail attached to the nanocraft. With 10 minutes of continuous laser power, the force of this light can accelerate a 1g nanocraft to 20% the speed of light. Such speeds can enable travelling to our nearest star neighbor in just 20 years. For the laser to effectively focus on the nanocraft after traversing the turbulence of Earth’s atmosphere, the Starshot system will need an Adaptive Optics system to ‘pre-correct’ the beam before transmission. To measure the distorting effects of the atmosphere, an artificial beacon must be placed high in altitude near the nanocraft through its launch. Proposed is a satellite-based laser guide star (SLGS) which will be attached to the mothercraft satellite which releases the nanocraft during launch. However, the satellite’s lateral and radial motion in the sky from the nanocraft threatens to introduce angular and focal anisoplanatic errors, respectively, that would make proper adaptive correction impossible. By creating a fully parameterizable orbital simulation of the mothercraft and nanocraft’s positions relative to the launch projector, it was found that there exist orbital configurations which keep these anisoplanatic errors within reason. One such orbit has an orbital period of 4 days and an eccentricity of 0.88. Following adaptive correction, it is vital that residual wavefront error does not introduce perturbances which cause the sail to fall out of the beam. Given that the sail behaves like a particle trapped in a potential well, a statistical model was created

Militaries have long used weapons with varying degrees of autonomy. However, recent technology advances have made possible more capable autonomous weapons, sparking calls by civil society groups and discussions in the United Nations (UN) on banning autonomous weapons. This thesis identifies potential military uses of autonomous weapons and makes prediction on their use through 2030. This is accomplished by analyzing past and present uses of autonomous weapons, ongoing technology developments, and developing an ontology for defining and describe autonomous weapons.