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Congratulations to Jake Letkemann!!

The best PDL paper award presented on the Aviation Forum 2026 in San Diego!

Letkemann, Sean Ellis, Enrique Chacon, A.Tropina, R.B. Miles, Laser Induced Plasma Near Surfaces in High-Speed Flows, AIAA Aviation 2026 Forum, 8-12 June, San Diego, CA, AIAA 2026-4050, https://doi.org/10.2514/6.2026-4050

Abstract

Hypersonic ablation via finite-rate surface chemistry produces carbon-containing gas-phase
species. It is well established that ablation involves a combination of oxidation, nitridation,
and sublimation, combined with mechanical erosion, particularly for carbon-based materials.
Despite the fact that chemical schemes are being developed to model ablation phenomenon for
flows in vibrational and thermochemical nonequilibrium, these models still require validation
against experimental data. For diagnostics based on laser plasmas it is worthwhile to provide
an analysis of possible effects caused by the creation of the plasma filament in a hypersonic flow.
In this paper, we provide a first attempt of such analysis, considering a temporal evolution of
the femtosecond laser filament in a hypersonic flow. The model includes a three-temperature,
ambipolar-diffusion CFD model of hypersonic flow with finite-rate surface chemical reactions
of ablation processes and detailed plasma kinetics. The main production and decay channels of
electronically excited nitrogen states are compared to those of the filament in ambient air. The
emission characteristics of electronically excited states of cyanide and diatomic carbon near the
surface are also explored.

 

” Imaging of Mini-Magnetosphere Formation Using Laser-Produced Plasmas”

Many-many thanks to the team of undergraduate students working in th ALLEMO Lab  (Spring  2026) with Dr. James Creel!!

 

Ella Gomez, Gregory Crowfoot, Larry Serrano

A set of laboratory experiments were performed to investigate, at reduced scale, the
interaction between the solar wind and Earth’s magnetic field that leads to the formation of the
magnetosphere. A 10-ns pulsed Nd:YAG laser operating at a wavelength of 1064 nm was focused
onto a copper target inside a low-pressure vacuum chamber to generate a laser-produced copper
plasma plume. A permanent spherical magnet was placed in the path of the expanding plasma
to represent a simplified dipole magnetic field, while a non-magnetized ball bearing was used as
a control case. High-speed imaging was used to visualize the time evolution of the visible plasma
emission as the plume propagated toward and around the sphere.

 

 

 

Many thanks to Jake Letkemann and Eben Anderson-Ciccone for their successful presentations on the Aviation Forum in Las Vegas!

Comparison of Surface Chemistry Models for the Calculation of Refractive Index Along Hypersonic Vehicle, https://arc.aiaa.org/doi/10.2514/6.2025-3481

Chemical kinetic schemes for ablating surfaces in a hypersonic flow were implemented as a boundary condition using the Park, ACA, and Z-A gas-surface models. The models were tested for the hypersonic flow at the RAM-C-II flight conditions. Good agreement was found between the plasma density in these models and the electron density data measured by RAM-C-II’s microwave reflectometers and electrostatic probe. Implementation of the ablation models showed strong increases in the refractive index near the 0.21-m cross section surface at 100 % in the Z-Amodel, 77 % in the ACA model, and 72 % in the Park model. Farther from the wall, small differences of about 3 % were also observable between models. The concentrations of the primary carbonaceous ablation products, the gradients and shapes of the species distributions were distinct between all three models, providing key characteristics for the model validation in future experiments using optical emission spectroscopy

Analysis of Magnetic Field Effects on Radio Signal Propagation Through Hypersonic Layer Plasma, https://arc.aiaa.org/doi/10.2514/6.2025-3849

This study investigates the propagation of a radio frequency (RF) signal through the hypersonic plasma layer for three cases such as Mach 15.5 flow at 30 km, Mach 12 flow at 20 km, and Mach 12 preheated flow. The main focus of the research is on the influence of the external magnetic field on the characteristics of wave transmission at various signal frequencies. A combined numerical approach including computational fluid dynamics (CFD), geometric optics, and the scattering matrix method (SMM) was used to simulate propagation of the RF signal through the hypersonic plasma layer near a wedge surface. It has been shown that at low signal frequencies the applied magnetic field led to a monotonic increase in signal transmission. In contrast, high-frequency signals exhibit a hybrid resonance phenomenon, where the transmission initially decreases with increasing magnetic field strength before recovering at larger magnetic field values. A distinct phase shift in the reflected wave is used to identify these resonance regions, suggesting potential for a diagnostic method of measuring plasma density in a hypersonic plasma layer.

Team from ALLEMO  on the Aviation Forum! The AIAA has a new logo!

(Form left to right: Dr. Miles, Dr. Tropina, Jake Letkemann, Eben Anderson-Ciccone, Lukas Robirds, Amir Rad).

Congratulations for Eben Anderson-Ciccone for successfully defending his MS thesis 

” Propagation of Radio Frequency Waves through Hypersonic Plasma Layer”,  19 May 2025.

In his work Eben used  a combination of computational fluid dynamics (CFD), ray tracing, and the scattering matrix method (SMM) to model radio frequency (RF) propagation through the hypersonic plasma layer identifying regions with the upper hybrid resonance.

We wish Eben success in all his future endeavors!

The non-paper session ” How to name a laser diagnostics ( Dr. Miles 80th)? has a great success with lots of participants and attendees!!

From left to write: Dr. Leonov, Dr. Michael, Dr. Yalin, Dr. Shneider, Dr. MILES, Dr. Adamovich,

Dr. Limbach, Dr.Tropina, Dr. Laux.

 

Great thanks to Dr. Sagar Pokharel presenting on the PDL session

” Plasma enhancement of fs-filament in 𝑁2-𝑂2 mixture with ns-heating pulse”.

Congratulations to Dr. Pokharel on his new journey as a Postdoc Research Associate   in the University of Texas at Austin!

Aviation Forum 2024, Las Vegas, 29 July- 2 August 

Great thanks to  Jake Letkemann, Juan Anaya and Eben Anderson-Ciccone for their excellent work and presentations!

1. J. Letkemann, A. Tropina, R.B. Miles, Analysis of Refractive Index Changes Near the Ablative Surface of Hypersonic Vehicles, Aviation Forum, 2024, 29 July- 2 August, Las Vegas, NV, AIAA-Paper 2024-3983.
2. E. Anderson-Ciccone, N. Sai Kolappan, A. Tropina, N. Tichenor, Optimization of Antenna Positions and Electromagnetic Mitigation Techniques in Hypersonic Flows, Aviation Forum, 2024, 29 July- 2 August, Las Vegas, NV, AIAA-Paper 2024-4310.
3. J. Anaya, A.Tropina, R.B. Miles, M.Grover, Interferometric study of air under thermochemical nonequilibrium,  Aviation Forum, 2024, 29 July- 2 August, Las Vegas, NV, AIAA-Paper 2024-4589.

From left to right;

Jake Letkemann -PhD student; Eben Anderson-Ciccone- MS student; Dr. Albina Tropina,

Juan Anaya – MS student ( MS thesis defense was in May 2024).

 

 

 

Congratulations to Sagar Pokharel for successfully defending his PhD degree!

“Self-consistent Modeling of Laser-induced Non-equilibrium Plasma”

21 May 2024, 2 pm, ALLEMO, Texas A&M University, Aerospace Engineering Department

   

Congratulations to Juan Anaya for successfully defending his Master’s degree!

ADVANCED LASER DIAGNOSTICS FOR REFRACTIVE INDEX MEASUREMENTS IN
                              HYPERSONIC FLOWS

May 20, 2024, 2 pm,  ALLEMO conference room, Texas A&M University

Motivation: Quantify aero-optical phenomena in hypersonic flows, focusing on how thermal and chemical non-equilibrium affect the refractive index of shock-heated air.

Thanks Sagar,  Juan and Hunter for excellent presentations on the SciTech 2024!

“Refractive index modification induced by femtosecond laser filament”;

and

“Refractive index field in high-speed flows: ionization effects”.

From left to to right:

Hunter Hadden – undergraduate student ( graduated May 2024);

Sagar Pokharel- PhD  student ( will graduate in August 2024);

Dr. Albina Tropina;

Dr. Richard Miles;

Juan Anaya- MS student ( will graduate in August 2024).

Congratulations to Sagar Pokharel with the new paper ” Self-consistent model and numerical approach for laser induced non-equilibrium plasma” published in the Journal of Applied Physics !

https://doi.org/10.1063/5.0175177

Great job!!

Numerical simulation of laser heating and evaporation of a single droplet.

Sagar Pokharel, Albina Tropina and Mikhail N. Shneider, “Numerical simulation of laser heating and evaporation of a single droplet”. Energies, 16(1),388 (2022); [https://doi.org/10.3390/en16010388]

The evaporation model, which was implemented in OpenFoam can be download from here:

https://drive.google.com/drive/folders/1g1qFV2XEiXGZQn6W_APhYKzRjmRm_fBa?usp=sharing

The work was partially supported by the Princeton Collaborative Research Facility (PCRF), supported by the U.S. Department of Energy (DOE) under Contract No.DE-AC02-09CH11466. Authors also acknowledge support from the U.S. DOE Office of Science Award No. DE-SC0022063.