Recently, the team of professors Ruan Shuangchen and Zhou Cangtao of Shenzhen University of Technology proposed a physical scheme for generating attosecond pulse and subperiodic coherent light shock radiation based on the wake field of superluminal plasma, and explained a new coherent radiation generation mechanism dominated by the collective action of electrons. The research was published in Physical Review Letters.
Electromagnetic radiation can be seen everywhere in life, such as sunlight and lights in the visible band, mobile phones and WIFI signals in the microwave band. However, light in nature is mostly incoherent, with complex frequencies, wide spatial orientation, and chaotic phases. In the 60s of the last century, humans invented the first coherent light source, the laser. The spectral components contained in the coherent light source have coherence, and the phase difference of each component is fixed, so the modulation and compression of the optical pulse can be realized, so as to obtain a coherent light source with extremely short duration and extremely high peak power, which is widely used in scientific research, industry and military to communications, entertainment and art.
The key to the production of coherent light sources is phase lock, that is, the phase between each microscopic particle involved in radiation is the same, and the generation of laser is based on the stimulated radiation principle proposed by Einstein, that is, atoms with the number of particles reversed will release outgoing photons consistent with the phase of the incident photon; and the free electron laser is a super-large scientific device based on the microbeam effect of the electron beam, so as to ensure that the motion phase of each electron is consistent. In nature, there is another wave phase-locking mechanism – shock wave.
For example, acoustic shocks are produced when a supersonic aircraft flies faster than the speed of sound in the air, because the sound waves generated by the head of the aircraft at different moments spread outward in a spherical wave, locking along a phase front at a special angle. Similarly, if the radiation source exceeds the speed of light, a new coherent electromagnetic radiation can be produced – light shock wave. However, it is impossible to make the same source of radiation faster than the speed of light in a vacuum, because special relativity states that the motion of any object cannot be “faster than the speed of light”.
In this study, Ruan Shuangchen and Zhou Cangtao’s team started from the basic principle of coherent radiation and proposed a new coherent radiation mechanism based on the collective action of electrons: through the interaction of the relativistic electron beam with the plasma with a slowly increasing density gradient, a plasma vacuole with a gradually smaller size can be excited, and the plasma electrons at different positions bounce at the tail end of the vacuole and radiate here, because the longitudinal size of the vacuole gradually shrinks, the collective speed of its tail end forward is greater than the driving electron beam speed, reaching “superluminal speed” conditions, so that the radiation produced here by different electrons is coherently superimposed along the Cherenkov angle to form a light shock wave.
According to reports, the radiation light source not only has a very short pulse width, reaching the attosecond scale, but also has a high intensity, proportional to the square of the propagation distance, and has excellent spatial directivity, extremely small angular astigmatism, stable carrier envelope phase and ultra-wide frequency tuning range. (Source: China Science News, Diao Wenhui)
Related paper information:https://doi.org/10.1103/PhysRevLett.131.145003
Schematic diagram of the principle of the radiation source generating shock waves (d) compared to other light sources Photo courtesy of the scientific research team