This video provides an update on the "Drone Killer 2.0" project, focusing on the challenge of safely testing its new, extremely powerful metal-cutting fiber lasers indoors. The first part of the video is a detailed technical tutorial on the operation of high-power fiber lasers, explaining concepts like ytterbium-doped double-clad fibers, which allow for immense power generation. It also covers the methods used to perfect the laser beam, including correcting for spherical aberration and astigmatism with simple optical windows and overcoming natural diffraction with an active focusing system that uses lidar for distance measurement and a piezoelectric actuator for rapid lens adjustment.
The second half of the video features a series of experiments to find a suitable protective backstop for the laser. A wide variety of materials are tested, including industrial products like rockwool, steel, and fire brick, as well as everyday items like plexiglass, ballistic gel, PVC foam board, paper, and various foods (banana, cucumber, potato, bread, egg). The tests reveal that materials with high water content offer significant resistance. The video concludes that two layers of water-soaked Medium Density Fiberboard (MDF) will be used as the safety backstop, as it provides a sufficient 4-second delay before burn-through, allowing ample time for safety systems to engage.
Testing High-Powered Lasers: A Quest for a Safe Backstop
0:37 - Project "Drone Killer 2.0": The video introduces an upgraded version of a previous project, which will use substantially more powerful, metal-cutting fiber lasers for targeting and destroying drones.
1:23 - The Safety Challenge: The new lasers are so powerful they can cut through the building, necessitating a reliable protective backdrop for safe indoor testing.
2:31 - How Fiber Lasers Work: A technical explanation begins, detailing how fiber lasers generate light. Diode lasers "pump" an active, ytterbium-doped fiber, causing it to fluoresce at the desired wavelength (1080 nm). For high power, a "double-clad" fiber is used to get more pump light into the active core.
7:05 - Correcting Beam Imperfections: The video explains how optical imperfections are corrected to maximize the laser's intensity at a distance. Spherical aberration is corrected using a simple glass window, while astigmatism is corrected by tilting the same window.
11:13 - Active Focusing System: To counteract the natural spreading of the beam (diffraction), an active focusing system is required. This system uses lidar to measure the target's exact distance and a fast piezoelectric actuator to adjust the focus in under a millisecond, ensuring maximum energy on target.
16:59 - Material Testing Begins: A series of tests demonstrates the laser's power against various materials.
17:04 - Rockwool, Steel, & Fire Brick: These materials offer almost no resistance, with the laser cutting through them instantly.
21:19 - Ballistic Gel: The high water content in ballistic gel absorbs significant energy, slowing the burn-through process and demonstrating the effectiveness of water in dissipating laser energy.
25:22 - High-Water-Content Foods: Tests on a banana, cucumber, potato, and egg show that they resist the laser for several seconds before it cuts through, further highlighting the protective qualities of water.
32:23 - PVC Foam Board: This material is surprisingly resilient, lasting nearly as long as the steel plate.
36:17 - The Chosen Solution: Water-Soaked MDF: The final and most effective solution tested is Medium Density Fiberboard (MDF) soaked overnight in water. A single sheet resists the laser for about 2 seconds. The plan is to use two sheets, providing a 4-second window for safety systems to shut down the laser before it can damage the building. This solution is low-cost, effective, and has low reflectivity.
38:36 - Fun with Energy Drinks: For fun, the laser is fired at cans of Red Bull and Monster energy drinks, causing them to rupture and spray their contents.