arXiv subjects

Yogeshwar Nath Mishra

Publications and source records attributed to Yogeshwar Nath Mishra.

4 recordsLinked to original sources

arXiv2025

Fovea Stacking: Imaging with Dynamic Localized Aberration Correction

The desire for cameras with smaller form factors has recently lead to a push for exploring computational imaging systems with reduced optical complexity such as a smaller number of lens elements. Unfortunately such simplified optical systems usually suffer from severe aberrations, especially in off-axis regions, which can be difficult to correct purely in software. In this paper we introduce Fovea Stacking , a new type of imaging system that utilizes emerging dynamic optical components called deformable phase plates (DPPs) for localized aberration correction anywhere on the image sensor. By optimizing DPP deformations through a differentiable optical model, off-axis aberrations are corrected locally, producing a foveated image with enhanced sharpness at the fixation point - analogous to the eye's fovea. Stacking multiple such foveated images, each with a different fixation point, yields a composite image free from aberrations. To efficiently cover the entire field of view, we propose joint optimization of DPP deformations under imaging budget constraints. Due to the DPP device's non-linear behavior, we introduce a neural network-based control model for improved alignment between simulation-hardware performance. We further demonstrated that for extended depth-of-field imaging, fovea stacking outperforms traditional focus stacking in image quality. By integrating object detection or eye-tracking, the system can dynamically adjust the lens to track the object of interest-enabling real-time foveated video suitable for downstream applications such as surveillance or foveated virtual reality displays

cs.CV↗

arXiv2025

Compressed Ultrafast Photography of Plasmas Formed from Laser Breakdown of Dense Gases Reveals that Internal Processes Dominate Evolution at Early Times

Compressed ultrafast photography (CUP) is applied to laser breakdown in argon and xenon under pressures up to 40atm to obtain 2D images of the plasma dynamics of single events with a spatial resolution of 250x100 pixels and an equivalent frame rate of 500 GHz. Light emission as a function of position and time is measured through red, green, blue, and broad-band filters. The spatially encoded and temporally sheared image normally used in CUP is now enhanced by the introduction of a constraint given by a spatially integrated and temporally sheared unencoded signal. The data yield insights into the temperature, opacity, the plasma formation process, and heat flow within the plasma and to the surrounding ambient gas. Contours of constant emission indicate that plasmas formed from sufficiently dense gas contract rather than expand despite having a temperature of a few eV. Plasmas formed from relatively low pressure gases such as 7atm argon can radiate with emissivity near unity. Modeling transport and opacity as arising from inverse Bremsstrahlung requires a degree of ionization that strongly exceeds expectations based on Saha's equation even as customarily modified to include density and screening. According to this model, both electrons and ions are strongly coupled with a plasma coefficient >1. During the first few nanoseconds after formation, Stefan-Boltzmann radiation and thermal conduction to ambient gas are too weak to explain the observed cooling rates, suggesting that transport within the plasma dominates its evolution. Yet, thermal conduction within the plasma itself is also small as indicated by the persistence of thermal inhomogeneities for far longer timescales. The fact that plasma is isolated from the surroundings makes it an excellent system for the study of the equation of state and hydrodynamics of such dense plasmas via the systems and techniques described.

physics.plasm-ph↗

arXiv2025

Latent Space Imaging

Digital imaging systems have traditionally relied on brute-force measurement and processing of pixels arranged on regular grids. In contrast, the human visual system performs significant data reduction from the large number of photoreceptors to the optic nerve, effectively encoding visual information into a low-bandwidth latent space representation optimized for brain processing. Inspired by this, we propose a similar approach to advance artificial vision systems. Latent Space Imaging introduces a new paradigm that combines optics and software to encode image information directly into the semantically rich latent space of a generative model. This approach substantially reduces bandwidth and memory demands during image capture and enables a range of downstream tasks focused on the latent space. We validate this principle through an initial hardware prototype based on a single-pixel camera. By implementing an amplitude modulation scheme that encodes into the generative model's latent space, we achieve compression ratios ranging from 1:100 to 1:1000 during imaging, and up to 1:16384 for downstream applications. This approach leverages the model's intrinsic linear boundaries, demonstrating the potential of latent space imaging for highly efficient imaging hardware, adaptable future applications in high-speed imaging, and task-specific cameras with significantly reduced hardware complexity.

eess.IV↗

arXiv2025

Electron-induced chemistry and sputtering of volatile species from amorphous and crystalline water ice

Electron irradiation of water-rich ices plays a significant role in initiating the chemical and physical processes on the surface of airless icy bodies in radiation environments such as Europa and Enceladus, as well as on the Moon, comets, and asteroids interacting with the solar wind. The sputtering process by electrons and ions leads to chemical modification and outgassing of their icy surfaces and the subsequent formation of a tenuous atmosphere. Though electron-sputtering yields are known to be lower compared to ion-sputtering yields, one needs to also account for their differential fluxes. In our experiments, the electron-induced sputtering yields of all the gaseous species H2, O, OH, H2O, and O2 are investigated for electron energies lower than 2 keV in terms of partial pressure vs. time of irradiation. The effective averaged change in partial pressure of the desorbed species is converted to the number of sputtered atoms or molecules per second per cm2 from the ice, and then to the sputtering yields (number of species sputtered per electron). Our data agrees well with the previously reported data for the sputtering of O2 and H2O yield for the amorphous ice. We also find that crystalline ice shows significantly lower sputtering yields when compared to amorphous ice, in agreement with the observation of similar trends in the literature. Our work indicates that sputtering yields per keV of O, OH, O2, and H2O drop with increasing electron energy from 0.5 keV to 2 keV.

astro-ph.EP↗