Research progress on the interaction between strong laser and matter Electromagnetic induced transparency effect in plasma physics

The transmission of electromagnetic waves (such as lasers) in plasma is a fundamental issue in plasma physics. In general, electromagnetic waves cannot be transmitted in high-density plasma, but their transmission and energy transfer play a crucial role in applications such as fast ignition laser fusion, laser particle acceleration, and ultra short and ultra bright radiation sources.

In 1996, S. from Stanford University E. Professor Harris, inspired by the concept of Electromagnetic Induced Transparency (EIT) in atomic physics, proposed the mechanism of EIT in plasma, which means that with the help of a high-frequency laser, low-frequency lasers that could not have been transmitted can be transmitted in high-density plasma. However, subsequent studies have shown that EIT cannot occur in real plasma with boundaries, but these studies are limited to the weak relativistic laser intensity range.

Recently, Li Yutong, a researcher from the Institute of Physics of the Chinese Academy of Sciences/National Research Center for Condensed Matter Physics in Beijing, and Wang Weimin, a research team from the Department of Physics of Renmin University of China, used the self-developed KLAPS particle simulation program to find that after low-frequency laser and relativistic intensity high-frequency laser hit the plasma at the same time, low-frequency laser can penetrate the plasma; However, when the polarization of the two lasers is perpendicular, this anomalous transmission phenomenon disappears, thus ruling out the common relativistic transparency effect. The research team developed a three wave coupling model under relativistic light intensity and provided the frequency passband of EIT occurrence. Under relativistic light intensity conditions, the width of the passband is sufficient to ensure stable transmission of low-frequency lasers; However, under weak relativistic light intensity conditions, the passband narrows into an isolated point, making it difficult to sustain its development. This explains why the EIT effect cannot occur under weak relativistic conditions in previous studies. This work demonstrates that the electromagnetic induced transparency effect that occurs in atomic physics can also occur in plasma physics. This phenomenon can be directly applied to double cone collision ignition (DCI) and fast flame laser fusion to improve laser coupling efficiency and fast electron yield.

The related research results were published on February 7, 2024 in the Physical Review Letters under the title "Electrically Induced Transparency in the Strong Relativistic Region". Zhang Tiehuai, a doctoral student of the Institute of Physics of the Chinese Academy of Sciences, is the first author of this article, Professor Wang Weimin of Renmin University of China and researcher Li Yutong of the Institute of Physics of the Chinese Academy of Sciences are the corresponding authors, and Academician Zhang Jie is the co author. The research topic comes from the "Research on New Laser Fusion Scheme" of the Chinese Academy of Sciences strategic leading science and technology special project (Class A) led by Academician Zhang Jie. The research has also been supported by the National Natural Science Foundation of China and other institutions.

Figure 1: The frequency spectrum of the laser field collected behind the bounded plasma region in [(a), (b)] and the evolution of the filtered laser field waveform over time in [(c), (d)], where different curves correspond to the incidence of bicolor field mixing, pure pump wave, and pure low-frequency wave. The evolution of laser field waveform over time during mixed incidence of two color fields after filtering, where the blue and red lines correspond to two cases of polarization parallel and vertical, respectively. The upper and lower rows correspond to two initial settings: high-density and low-density.

Figure 2: The analytical model shows the dispersion relationship of Stokes wave dominant branches under (a) high-density and (b) low-density settings, with a wider passband (highlighted in bright yellow) appearing in (b). (c) The one-dimensional PIC simulation results under different light intensities after fixing the ratio of initial plasma density to effective critical density are consistent with the EIT passband positions provided by the model. (d) The PIC simulation results provide the passband positions under different light intensities and density settings.

Figure 3: Evolution of Stokes wave (blue line, left axis), anti Stokes wave (black line, left axis), and pump wave (red line, right axis) signal intensities with spatial position. Under initial conditions, the plasma is uniformly distributed at 10 λ 0

Source: OFweek