arXiv subjects

Grover A. Swartzlander Jr

Publications and source records attributed to Grover A. Swartzlander Jr.

12 recordsLinked to original sources

arXiv2023

Broadband Diffractive Solar Sail

The transverse radiation pressure force and acceleration is compared for two parametrically optimized designs: prismatic and two-pillar metasurface gratings. The numerical results were cross-verified with both Maxwell stress tensor and modal analysis. Solar blackbody irradiance was assumed for wavelengths ranging from 0.33 [um] to the grating cutoff at 1.5 [um], encompassing 83% of the solar constant. This multi-objective optimizer study found that neither design comprised Si3N4 performed as well as those corresponding to a low refractive index, low mass density material. The predicted transverse acceleration of the optimized low-index metasurface grating is compared to that of a state-of-the-art reflective solar sail.

physics.optics↗

arXiv2023

High Forward Thrust Metasurface Beam-Riding Sail

The radiation pressure force and torque on a one-dimensional bi-grating composed of a Si-SiO_2 high contrast binary metagrating is analyzed for the purpose of stable beam riding whereupon a high power laser having an expanding Gaussian irradiance distribution propels the grating in outer space, free from gravitational forces. The binary metagrating structure has been simultaneously optimized to afford high forward thrust, and corrective restoring forces and torques in the event of small linear and angular disturbances. We demonstrate that stability may be enhanced at the expense of forward thrust. The validity of our metamaterial findings is reinforced owing to good agreements between finite-difference time-domain and finite element numerical methods. To reduce mass and enhance forward acceleration this laser-driven sail was designed to be free of a stabilizing boom.

physics.optics↗

arXiv2022

Theory of Radiation Pressure on a Diffractive Solar Sail

Solar sails propelled by radiation pressure enable space missions that cannot be achieved using chemical rockets alone. Significant in-space propulsion for missions such as a solar polar orbiter may be achieved with a sail that deviates sunlight at a large average angular direction. The momentum transfer efficiency of sunlight diffracted from a sun-facing diffractive sail comprised of periodic sawtooth prism elements is examined here. The spectrally averaged efficiency is found to approach that of a monolithic prism when the grating period is much longer than the peak of the solar spectrum. This idealized diffraction analysis predicts a greater transverse radiation pressure force compared to an idealized reflective sail. With modern optical design and fabrication techniques, diffractive solar sails may one day replace reflective sails.

physics.optics↗

arXiv2018

Flying on a Rainbow: A Solar-Driven Diffractive Sailcraft

Radiation pressure afforded by natural broadband sunlight upon a transmissive diffractive sail is theoretically and numerically investigated. A grating period of one micrometer is found to convert 83% of the solar black body spectrum into sailcraft momentum. Non-optimized orbit-raising trajectories for diffractive and reflective sails are compared. Potential advantages of diffractive sails are also described.

physics.pop-ph↗

arXiv2018

Measurements of Radiation Pressure owing to the Grating Momentum

The force from radiation pressure owing to the grating momentum was measured for a thin transmissive fused silica grating near the Littrow angles at wavelengths of 808 nm and 447 nm. A significant magnitude of force was measured in the direction parallel to the grating surface. We also confirmed that the component of force normal to the grating surface may vanish. This forcing law is characteristically different from radiation pressure on a reflective surface, and thus, opens new opportunities for light-driven applications such as solar or laser driven sailcraft, or the transport of objects in liquids.

physics.optics↗

arXiv2017

Radiation Pressure on a Diffractive Sailcraft

Advanced diffractive films may afford advantages over passive reflective surfaces for a variety space missions that use solar or laser in-space propulsion. Three cases are compared: Sun-facing diffractive sails, Littrow diffraction configurations, and conventional reflective sails. A simple Earth-to-Mars orbit transfer at a constant attitude with respect to the sun-line finds no penalty for transparent diffractive sails. Advantages of the latter approach include actively controlled metasails and the reuse of photons.

physics.optics↗

arXiv2016

Randomized Aperture Imaging

Speckled images of a binary broad band light source (600-670 nm), generated by randomized reflections or transmissions, were used to reconstruct a binary image by use of multi-frame blind deconvolution algorithms. Craft store glitter was used as reflective elements. Another experiment used perforated foil. Also reported here are numerical models that afforded controlled tip-tilt and piston aberrations. These results suggest the potential importance of a poorly figured, randomly varying segmented imaging system.

astro-ph.IM↗

arXiv2015

Optimized focal and pupil plane masks for vortex coronagraphs on telescopes with obstructed apertures

We present methods for optimizing pupil and focal plane optical elements that improve the performance of vortex coronagraphs on telescopes with obstructed or segmented apertures. Phase-only and complex masks are designed for the entrance pupil, focal plane, and the plane of the Lyot stop. Optimal masks are obtained using both analytical and numerical methods. The latter makes use of an iterative error reduction algorithm to calculate "correcting" optics that mitigate unwanted diffraction from aperture obstructions. We analyze the achieved performance in terms of starlight suppression, contrast, off-axis image quality, and chromatic dependence. Manufacturing considerations and sensitivity to aberrations are also discussed. This work provides a path to joint optimization of multiple coronagraph planes to maximize sensitivity to exoplanets and other faint companions.

astro-ph.IM↗

arXiv2014

Vortex-phase filtering technique for extracting spatial information from unresolved sources

A white light vortex coronagraph was used to experimentally achieve sub-resolution detection. The angular location of the centroid, $γ$, and the angular extent of circular pinhole sources, $Θ$, were measured to within errors of $δγ= \pm0.015\,λ/D$ and $δΘ= \pm0.026\,λ/D$. This technique has two advantages over conventional imaging: simple power measurements are made and shorter exposure times may be required to achieve a sufficient signal-to-noise ratio.

physics.optics↗

arXiv2014

Nodal Areas and Structured Darkness

Generalized beams of light that are made to turn inside out, creating black nodal areas of total destructive interference are described. As an example we experimentally created an elliptical node from a uniformly illuminated elliptical aperture by use of a lossless phase mask called a q-plate. We demonstrate how a modified phase retrieval algorithm may be used to design phase masks that achieve this transformation for an arbitrary aperture shape when analytical methods are not available. This generic wave phenomenon may find uses in both optical and non-optical systems.

physics.optics↗

arXiv2004

Spatial coherence singularities and incoherent vortex solitons

We study spatially localized optical vortices created by self-trapping of partially incoherent light with a phase dislocation in a biased photorefractive crystal. In a contrast to the decay of coherent self-trapped vortex beams due to the azimuthal instability, the incoherent vortices are stabilized when the spatial incoherence of light exceeds a certain threshold. We analyze the spatial coherence properties of the incoherent optical vortices and reveal the existence of ring-like singularities in the spatial coherence function of a vortex field that can characterize the stable propagation of vortices through nonlinear media.

nlin.PS↗

arXiv2004

Spatial coherence singularities of a vortex field in nonlinear media

We study the spatial coherence properties of optical vortices generated by partially incoherent light in self-focusing nonlinear media. We reveal the existence of phase singularities in the spatial coherence function of a vortex field that can characterize the stable propagation of vortices through nonlinear media.

nlin.PS↗