Search NASA⌕ Search

Engineering topics

Ly, Sonny S.

Publications and source records attributed to Ly, Sonny S..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Laser drilling and machining enhancement using gated CW and short pulsed lasers

The present disclosure relates to a laser system for processing a material. The system may make use of a laser configured to intermittently generate a first laser pulse of a first duration and a first average power, at a spot on a surface of the material being processed, and a second laser pulse having a second duration and a second peak power. The second duration may be shorter than the first duration by a factor of at least 100, and directed at the spot. The second laser pulse is generated after the first laser pulse is generated. The first laser pulse is used to heat the spot on the surface of the material, while the second laser pulse induces a melt motion and material ejection of molten material from the melt pool.

Ly, Sonny S.↗
DOE OSTI2022

Investigating laser ablated plume dynamics of carbon and aluminum targets

Recently acquired high-resolution images of nanosecond laser ablation plumes suggest a strong correlation between the internal plume structure and the type of material being ablated. However, the details of this relation are currently not well understood. In this work, we attempt to explore this correlation using a 2D radiation hydrodynamics model to study the dependence of internal plume structure formation on the ablation material. Here spatio-temporal emission maps and plume expansion velocities from experimental measurements are compared with the model predictions, including synthetic emission maps. The shape and expansion rate of an outer air plume region are found to be in good agreement for both carbon and aluminum, as are the inner material plume dynamics for carbon ablation. The largest disagreement is observed in the case of a polished aluminum target, where the chaotic inner plume features seen in the experimental images are not observed in the model. The possible physical mechanisms responsible for this discrepancy are discussed. This effort constitutes a continued development toward a predictive model of ablation plume dynamics and chemistry for various materials in extreme environments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Wavefront shaping with a Hadamard basis for scattering soil imaging

Here, soil is a scattering medium that inhibits imaging of plant-microbial-mineral interactions that are essential to plant health and soil carbon sequestration. However, optical imaging in the complex medium of soil has been stymied by the seemingly intractable problems of scattering and contrast. Here, we develop a wavefront shaping method based on adaptive stochastic parallel gradient descent optimization with a Hadamard basis to focus light through soil mineral samples. Our approach allows a sparse representation of the wavefront with reduced dimensionality for the optimization. We further divide the used Hadamard basis set into subsets and optimize a certain subset at once. Simulation and experimental optimization results demonstrate our method has an approximately seven times higher convergence rate and overall better performance compared to that with optimizing all pixels at once. The proposed method can benefit other high-dimensional optimization problems in adaptive optics and wavefront shaping.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Controlling AM spatter and conduction

An intelligent feed forward model to control additive manufacturing (AM) laser powder bed fusion process and reduce spattering whereby defects are eliminated by controlling the laser power and reducing spattering through a computer model. This application describes using a proportional integral derivative (PID) controller to create a power map that reduces spattering.

Khairallah, Saad A.↗