The Chinese work with advanced sound lasers.

"The microsphere, levitated by the dual beam optical tweezer (green), is driven by the active optomechanical system (red) to generate nonlinear phonon lasers (colored waves). Meanwhile, the injected electrical signal, represented by the white lightning mark, acts as a simple but powerful way to enhance the quality of the nonlinear phonon laser, shown as the colored spectrum. Credit: Guangzong Xiao, Tengfang Kuang, Yutong He, Xinlin Chen, Wei Xiong, Xiang Han, Zhongqi Tan, Hui Luo, Hui Jing" (ScitechDaily, Chinese Scientists Unveil the World’s Most Powerful Sound Laser)

Any material that is either tight enough or has an echo space inside it can be used as a nanoparticle that forms the soundwaves. The requirement for that material is that it is homogenous. In some models, there are the nano-balls and there is the small tube in the center of the ball. The system sends energy impulses to the nanoball and then that ball sends acoustic impulses to the center of it. 

The tube and nanopyramid in it can aim acoustic waves in the right direction. The system can also use things like liquids and whirl around the acoustic tube. The system shoots resonating waves to that whirl. The whirl should be homogenous so, the liquid can be liquid hydrogen or nitrogen. The system can send acoustic waves through that liquid. In some other models. There are lots of fullerene balls. The system is used to make coherent sound waves. 

The diagram of the laser. In sound amplification by stimulated emission of radiation, SASER, the system uses a similar structure to create acoustic waves. There are many methods to make that coherent sound wave. 

Chinese researchers created the most powerful acoustic lasers in the world. The new acoustic laser base is in the nanostructures that the laser rays will put to oscillate. The homogenous echo chambers can be around the tube. And the system sends the soundwave from the bottom. The side-coming soundwaves inject energy and push the acoustic waves into a tight and coherent form. 

"The measured power spectrum (PSD) of phonons shows more than 3 orders enhancement in brightness and narrowed linewidth, revealing wide application scenarios covering audible and ultra-sound scope. Credit: Guangzong Xiao, Tengfang Kuang, Yutong He, Xinlin Chen, Wei Xiong, Xiang Han, Zhongqi Tan, Hui Luo, Hui Jing"  (ScitechDaily, Chinese Scientists Unveil the World’s Most Powerful Sound Laser)

The difference between acoustic and electromagnetic waves is the size of oscillating particles. In acoustic waves the system makes atoms or molecules oscillate. The acoustic laser can use the oscillating diamond or carbon crystals to make the coherent acoustic wave. The difference between electromagnetic and acoustic waves is that acoustic waves don't heat objects. 

The nanotube-based acoustic lasers can be used to create the SONAR CCD systems. Those high-accurate sonars can used for many purposes from medical to military applications. 

That makes the acoustic wave, that acts like a laser ray. The idea of Sound amplification by stimulated emission of radiation, SASER is the same as laser rays. Rather saying, SASERs look like masers rather than lasers. The wave movement or energy beam travels through a tube. There the oscillation systems pump energy into it. 

"The phonon laser boosts the phononics to coherent regime with wider frequency range, thus can achieve higher accuracy and further broaden the application scenarios, such as lesion identification of multiform organs and tissues, deep-sea detection of flora and fauna. Credit: Guangzong Xiao, Tengfang Kuang, Yutong He, Xinlin Chen, Wei Xiong, Xiang Han, Zhongqi Tan, Hui Luo, Hui Jing" (ScitechDaily, Chinese Scientists Unveil the World’s Most Powerful Sound Laser)

And if we look at the diagram of the laser systems the lightning tube must only replaced by loudspeakers or acoustic resonators. In lasers, those lightning tubes create light, that amplifies a laser ray, that travels in the laser tube. There are two mirrors on both sides of the laser tube. The light jumps between those mirrors and lighting tubes pump energy into that stading wave.

Nanotechnology makes it possible to create nanotube structures where so-called nanocrystals inject acoustic waves into the nanotube. The crystal at the bottom sends the wave that the system amplifies. In some models, the system uses a "lightning tube" that is filled with liquid or some kind of vapor. 

There could be nano-bubbles in those tubes and then the system can make those bubbles oscillate. There is the possibility of replacing mirrors using the loudspeakers. Those loudspeakers make standing waves between them. Then the system opens the loudspeakers and releases that soundwave.  

In some other models, the acoustic wave travels in the central tube of the structure. There are atom or molecule chains in tubes around the central tube. The outcoming energy makes those atom chains oscillate and that sends energy into the center of the central tube. And then there is the acoustic stress resonance from the bottom of that chain. That resonance aims at the acoustic beam. 

There are lots of applications for the SASER systems. Those systems can create extremely accurate ultra-sound research. Or they can act in the deep sea research. 

https://scitechdaily.com/chinese-scientists-unveil-the-worlds-most-powerful-sound-laser/

https://en.wikipedia.org/wiki/Sound_amplification_by_stimulated_emission_of_radiation