The Science and Potential of Laser-Induced Plasma Sound Generation
In the realm of sound generation and acoustic technologies, there's a phenomenon that has recently captured the attention of scientists and defense agencies alike – laser-induced plasma sound generation. This technology involves the manipulation of plasma using lasers to create sound, and while it sounds like something out of a science fiction novel, it's very much grounded in reality.
Understanding Plasma Speakers
Before diving into the details of laser-induced plasma sound generation, let's first explore a related technology – plasma speakers. Plasma speakers, also known as ionophones, are a type of loudspeaker that employs electrical plasma to vary air pressure, instead of using a solid diaphragm like in traditional speakers.
In these devices, a plasma arc is created which heats the surrounding air causing it to expand. By varying the electrical signal that drives the plasma – a signal that is connected to the output of an audio amplifier – the size of the plasma varies, which in turn changes the expansion of the surrounding air. The result? Sound waves are created.
Compared to conventional loudspeakers, plasma speakers have several unique advantages. Because the plasma is virtually massless, it lacks the inertia inherent in traditional speaker designs, allowing for exceptional transient response and accuracy even at higher frequencies. However, due to their low mass, they are more effective as tweeters as they are unable to move large volumes of air unless there is a large number of plasma entities.
Enter Lasers
Now that we understand the basics of plasma speakers, let's delve into the fascinating world of laser-induced plasma sound generation. The concept involves using two lasers: one to generate a ball of plasma when it hits the target, and another to modulate that plasma ball in open air. This modulated plasma ball can generate a loud sound, with an intensity as high as 140 dB at the target area, equivalent to the sound of fireworks or a shotgun going off at close distance.
In the future, researchers aim to refine the secondary modulation laser to play audio over the plasma. This could potentially turn the beam into a directed loud speaker. Only the target would be able to hear the audio, opening up intriguing possibilities for defensive applications such as non-violent deterrents.
The Talking Fireball
The concept of a “talking fireball” has also been explored, where lasers are pulsed to modulate the sound produced by plasma to carry coherent speech. This so-called “Voice of God” was once considered to be the stuff of rumors and speculation, but recent developments suggest that it might not be as far-fetched as it once seemed. In 2018, the Pentagon’s Joint Non-lethal Weapons Program released a video of a short-pulse laser creating a talking plasma fireball, signifying that the concept was not entirely theoretical.
Conclusion
While the technology of laser-induced plasma sound generation might seem like it's straight out of a sci-fi movie, it's a testament to the incredible strides we are making in the field of acoustics and sound generation. As researchers continue to refine these techniques, we may soon see these “talking lasers” deployed in a variety of applications, from defense mechanisms to new forms of communication. The future of sound is here, and it's absolutely electrifying.
Further Reading:
https://wikiless.org/wiki/Plasma_speaker?lang=en
https://hackaday.com/2018/03/24/us-military-developing-laser-plasma-speakers/
Here, you can find the in-depth article:
A radical new laser-powered sonic weapon was demonstrated at the “Directed Energy to DC Exhibition”. This weapon utilizes a system with two lasers: one creates a ball of plasma when it impacts the target, and the other modulates this plasma ball in open air. The system functions similarly to a plasma speaker, where plasma acts as a driver for a massless speaker. Currently, the system can generate a deafening crack at the target area, with a measured intensity of up to 140 dB. This is as loud as fireworks or a shotgun firing at close proximity, and could theoretically be used to deter anyone targeted by the beam.
In the future, researchers aim to enhance their secondary modulation laser to the point where it can transmit audio over the plasma. This would enable the beam to function as a sort of directed loudspeaker, potentially useful for defensive applications. Only the target would be able to hear the audio, which might be a recording telling them they have entered a secured area. The idea of a disembodied voice instructing you to turn around could serve as a highly effective non-violent deterrent.
The technology takes advantage of plasma speakers or ionophones, which alter air pressure via an electrical plasma instead of a solid diaphragm. The plasma arc heats the surrounding air, causing it to expand. By modifying the electrical signal that drives the plasma, which is connected to the output of an audio amplifier, the plasma size varies. This, in turn, changes the expansion of the surrounding air, creating sound waves. In comparison to conventional loudspeakers, plasma speakers as members of the family of massless speakers, don't have physical limitations inherent in their design.
However, there are practical considerations for plasma speaker designs. They ionize ambient air which contains the gases nitrogen and oxygen. These gases can produce reactive by-products in intense electrical fields, potentially reaching hazardous levels in closed rooms. The two primary gases produced are ozone and nitrogen dioxide.
The lasers create a plasma by tearing apart molecules in the air, producing a glowing ball of fire in the sky. This plasma ball can be shifted back and forth at high speed by moving the laser beams around the sky. The lasers can be pulsed to modulate the crackling sound produced by the plasma to carry coherent speech.
This could potentially be used for psychological operations, with a seemingly divine voice commanding opponents to flee or surrender. While this technology is possible in the lab, it would be very difficult to produce in the sky. However, in 2018, the Pentagon's Joint Non-lethal Weapons Program released a video of a short-pulse laser creating a talking plasma fireball, suggesting that this project is not complete fantasy.