This video documents the development and testing of a lightweight, practical safety backstop for a high-power fiber laser used in a directed energy weapon project. Faced with the challenge that a conventional concrete barrier would be impractically heavy, the experiment explores using water's high heat capacity as a laser-absorbing medium. To solve the problem of containment and prevent high-pressure spray upon puncture, water is stabilized into a gel using the superabsorbent polymer sodium polyacrylate. A series of test panels are fabricated to compare the performance of a plain gel against gels modified with silicon dioxide and titanium dioxide nanoparticles, intended to diffuse the laser beam via Mie scattering. Panels with additional backings of thin concrete and aluminum are also tested. The results conclusively show that a simple panel composed of a hardboard front, a plain sodium polyacrylate gel core, and an aluminum backplate is the most effective and practical solution, withstanding the 20 million watts/cmΒ² laser beam for an extended duration without penetration.
Developing a High-Power Laser Safety Barrier
00:01:06 The Problem: Laser Safety: The project requires a safety backstop for a powerful fiber laser (delivering intensities of 20 million watts per square centimeter) used to destroy drones. A conventional backstop is needed to prevent the laser from burning through the building if it misses its target.
00:02:44 The Challenge: An Impractical Solution: A traditional concrete barrier for the required 20-square-meter area would weigh over 12 tons, making it too heavy and impractical for the indoor facility.
00:03:21 Inspiration from Nature: Earlier experiments revealed that materials with high water content, like a cucumber, are surprisingly effective at absorbing laser energy due to water's high heat capacity and energy of vaporization.
00:05:06 The Proposed Solution: A Water-Based Gel: To use water as a barrier without the risk of high-pressure spray from a puncture, the solution is to use sodium polyacrylate, a superabsorbent polymer, to turn the water into a stable, semi-solid gel.
00:07:05 Experimental Design: Several test panels are constructed to systematically evaluate different configurations:
Control Panel: Hardboard with an air gap.
Plain Gel: Filled with the sodium polyacrylate gel.
Enhanced Gels: Gels mixed with silicon dioxide or titanium dioxide nanoparticles to test if Mie scattering will diffuse the laser and improve performance.
Backed Panels: Panels with thin concrete or aluminum backplates to test their contribution to stopping the beam.
25:00 Test 1 - Control vs. Plain Gel: The control panel with an air gap is penetrated in less than a second. In contrast, the plain gel panel withstands the laser for over three minutes without failure, proving the core concept is exceptionally effective.
30:17 Test 2 - Nanoparticle Performance: The silicon dioxide gel performs well, similar to the plain gel. However, the titanium dioxide gel fails in under a minute, creating significantly more sparks and proving to be a detrimental additive.
33:44 Test 3 - Concrete Backing: A panel with a concrete backing fails relatively quickly, demonstrating that adding a thin concrete layer provides no significant benefit and adds unnecessary weight and complexity.
38:13 Test 4 - Aluminum Backing: The panel with an aluminum backplate is the clear winner. The aluminum gets hot enough to glow but does not melt through, successfully conducting and radiating the heat from the diffused laser beam.
43:19 The Final Design: The conclusion is that the optimal, lightweight, and effective solution is a panel constructed with a hardboard front, a simple sodium polyacrylate gel core (without any additives), and an aluminum backplate. This design provides robust protection and is self-sealing, as the gel does not leak out after being punctured.