Lasers with large coherence lengths are very expensive. The larger this distance, the narrower the bandwidth of the laser (more monochromatic). This distance is called the “coherence length”. Because the photons in the laser have wavelengths that are nearly identical - but not a perfect match - they will begin to get noticeably out of phase with each other after traveling some distance. The photons coming from LEDs are not produced this way, even if the light is nearly all the same color. This what is meant by the term “coherent light”. When this happens, the 2nd photon is in phase with the first photon and moves in the same direction. A laser emits light by a process called “stimulated emission”, where the photon resulting from the decay of one excited quantum state “stimualtes” another nearly identical quantum excited state to also decay, and thus lose a photon of almost the same amount of energy. Posted in Arduino Hacks, Laser Hacks Tagged chronograph, CoilGun, laser Post navigation Or, you might prefer a more futuristic look. If you need a coilgun, we always liked the looks of this one. 22 caliber round will have a muzzle velocity of well over 300 meters per second, but, still, 120 to 130 meters per second is nothing to sneeze at. How fast was the coil gun? Well over 100 meters per second. It seems like a photodiode or transistor would be more accurate and have better sensitivity to the laser or even just a conventional light source. We also thought the response time and wavelength sensitivity of light-sensitive resistors might be a bit off. We also thought it would be nice to add some sort of encoder to let the device measure the distance between sensors automatically since it is adjustable. We couldn’t help but wonder if a first surface mirror might have worked better. We liked the mechanical design and the way he managed pushbuttons in the 3D printed case. That worked, so all that was left was a nice mechanical design to allow changing the height of the sensors and the distance between the sensors. The final answer was to use an array of detectors and removed the laser’s collimation lens to cover a wider area. The first attempt to rectify this used mirrors, but the loss was too great - we suspect he was using a second surface mirror. As it turns out, there are some issues to resolve.įor one thing, a laser is too narrow and might miss the projectile. A laser and a light sensor would mark the entry and exit of the projectile over a known distance. Built a coil gun and the obvious question is: how fast is the projectile? To answer it, he built a chronograph suitable for timing a bullet.
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