Laser Beam Propagation in Maritime Environment Study

Investigation and comparison of laser beam propagation in maritime environments through field and laboratory experiments. The study examines the effects of real-life conditions such as temperature fluctuations, wind, and aerosols on laser light propagation. A basic field experiment at the US Naval Academy and weather conditions at College Creek are analyzed to understand light intensity fluctuations. Measurements focus on recording laser light intensity fluctuations at the source and target, utilizing statistical analysis due to the challenges of instrumenting the entire propagation path outside the laboratory setting.

• Laser Beam Propagation
• Maritime Environment
• Field Experiments
• Laboratory Experiments
• Light Intensity Fluctuations

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1. Laser Beam Propagation in Maritime Environment Svetlana Avramov-Zamurovic Olga Korotkova Reza Malek-Madani 1 ONR meeting 9/17/2024

2. Investigation Method Laser Beam Propagation in Maritime Environment Modeling (Mathematics) Field Measurements (Engineering) Physical Phenomenon: Laser Propagation (Physics) 2 ONR meeting 9/17/2024

3. Field experiments vs. Laboratory Experiments in the laboratory provide controlled environment for studding physical phenomena. Experiments often set up to observe a single parameter at the time. Parameters could be changed independently from the rest of the environment to isolate a particular effect. Drawback: Even in the extraordinarily complex and resource rich laboratory not all of the influential parameters of the maritime environment are included. Field experiments provide the real-life conditions of the environment on laser light propagation. True environmental changes along the entire path are occurring simultaneously and influence laser light propagation. Temperature fluctuations, wind, aerosols, etc. 3 ONR meeting 9/17/2024

4. Basic Field Experiment at USNA Source: High quality beam shape (He-Ne red laser, Gaussian beam) Low power laser (4mW), Midshipmen safety Beam diameter suitable for medium range propagation (d=1cm) Beam splitter and camera sensor used to observe beam statistics Medium: Maritime environment at US Naval Academy grounds (propagation across body of water and above field, 500m source-target distance) Target: Light intensity fluctuations recorded at the beam center (observed directly using camera sensor) 4 ONR meeting 9/17/2024

5. College Creek Test Weather conditions at Hospital Point on June18, 2010 Sea Level Pressure Wind Speed Gust Speed Time Temp Humidity Wind Dir Conditions: 9:54 AM 73.0 F 57% 30.13 in North none none Clear 10:54 AM 75.0 F 53% 30.13 in none none none Clear 5 ONR meeting 9/17/2024

6. Measurements : Light Intensity Fluctuations Objective: Laser light intensity fluctuations due to beam propagation through maritime environment are recorded at the source and at the target. Statistical approach to analyze the beam propagation is the only practical solution because it is impossible to instrument with sensors the environment along the entire propagation path outside of laboratory. Actual measurement parameters: Area of observation 1cm2 at the beam center (stacked frames) Spatial resolution far less than correlation distance due to high pixel resolution of the camera s sensor Frame speed: realizations captured at the maximum rate of 1 kHz 3-5 minutes of continuous observations recorded Weather parameters documented at target 6 ONR meeting 9/17/2024

7. Model: Probability Density Function The goal: Deliver laser light energy onto a target by maintaining the highest level of light intensity for as long as necessary to interfere with the target. Environmental influences cause light intensity to fluctuate. Probability Density Function provides information on how often particular light intensity occurs at the beam center, making PDF a model of choice to measure the beam quality on the target. PDF contains the information about the properties of the environment the laser light passed through. The method: PDF models are based on light scattering physics employing various mathematical functions and on statistical moments calculated from data. Data histogram is used to evaluate the fidelity of a PDF model. 7 ONR meeting 9/17/2024

8. Outcomes Six field experiments successfully executed. Students engaged in experimental aspect of the project: MIDN Iiams independent research studies Field experiments are used as a laboratory exercise Control systems and their application to weapons course, A week per semester, 2 semesters, 3 sections, 50 students Directed Energy course A week per semester, 2 semesters, 30 students Four PDF models investigated: Gamma-Gamma and Log-Normal by Andrews and Philips, Gamma- Laguerre by Barakat and Rice Nakagami modification by Beckman Data processing programs developed in MATLAB. PDF allowed us to clearly establish the difference between laser beam propagation above water and over land. Major project achievements published in a leading journal paper. 8 ONR meeting 9/17/2024

9. Laser light propagation above the water and above the land Land Water Normalized Intensity 9 ONR meeting 9/17/2024

10. Publications Journal Olga Korotkova, Svetlana Avramov-Zamurovic, Reza Malek-Madani, and Charles Nelson, "Probability density function of the intensity of a laser beam propagating in the maritime environment," Opt. Express 19, 20322-20331 (2011) Conference Proceedings Svetlana Avramov-Zamurovic ,Olga Korotkova and Reza Malek-Madani, Probability Density Function Of Fluctuating Intensity of Laser Beam Propagating in Marine Atmospheric Turbulence , SPIE Photonics West Sensing Conference proceedings, Atmospheric and Oceanic Propagation of Electromagnetic Waves V, Volume 7924, (2011). C. Nelson, S. Avramov-Zamurovic, R. Malek-Madani, O. Korotkova, R. Sova, F. Davidson, PDF computations for power-in-the-bucket measurements of an IR laser beam propagating in the maritime environment , SPIE Defense, Security, and Sensing Conference proceedings, 2011. Presentations Svetlana Avramov-Zamurovic, Olga Korotkova and Reza Malek-Madani, Laser Beam Characterization of Propagation through a Marine Atmospheric Channel , Thirteenth Annual Directed Energy Symposium, November 2010. Svetlana Avramov-Zamurovic ,Olga Korotkova and Reza Malek-Madani, Probability Density Function Of Fluctuating Intensity of Laser Beam Propagating in Marine Atmospheric Turbulence , SPIE Photonics West Sensing Conference, January 2011. Reza Malek-Madani, Svetlana Avramov-Zamurovic, Olga Korotkova and Joe Watkins, An experimental study of the probability density function of a turbulence induced fluctuating laser beam , Directed Energy Beam Control Conference, May 2011. 10 ONR meeting 9/17/2024

11. Next steps Education: Recruiting effort this fall resulted in three midshipmen already engaged in basic experimental work with a goal to start independent research projects in spring. Introduction to MATLAB programming as applied to modeling and processing experimental data: a new 1 credit course offered to plebes. Motivation: the first lecture will be collecting laser propagation data in HYDRO LAB. Research: To control light intensity delivery on the target modulate the light at the source SPACE domain: Pixel by pixel amplitude and phase modulation TIME domain: Frame by frame modulation Technical Support: Technician dedicated to the project made significant progress in establishing instrumentation equipment functionality. New instruments to be integrated into the project SPACE domain : Spatial Light Modulator TIME domain : Liquid Crystal Optical Modulators Polarimeter 11 ONR meeting 9/17/2024