Influence Of Femtosecond Filaments Array On Radio Frequency Electromagnetic Wave Propagation

When the intense femtosecond laser pulses propagate in the atmosphere a long plasma filament will be formed with a length longer than the corresponding Rayleigh length.Since people discovered this phenomenon,researchers have conducted extensive research on the characteristics and applications of femtosecond filaments.Because femtosecond laser filaments have good electrical conductivity,it can interact with radio frequency electromagnetic waves.Make it play an extremely important role and indispensable important value in many fields such as radio frequency energy transmission,plasma stealth,lidar.Therefore,it is important to studied the effect of femtosecond laser filaments array on the transmission of radio frequency electromagnetic waves.According to the physical characteristics of femtosecond laser filaments,the influence of plasma filaments array on radio frequency electromagnetic wave transmission is deeply studied.In addition,finite-difference time-domain(FDTD Solutions)is used to establish the geometric model of femtosecond laser plasma filaments array and radio frequency electromagnetic wave,and the reflection efficiency of electromagnetic wave incident on femtosecond filaments array under different experimental conditions is simulated.The influence of plasma filaments array with different spacings on electromagnetic wave reflectivity under different incident angles of radio frequency electromagnetic wave is studied.In the theoretical research on the influence of femtosecond laser plasma filaments array on radio frequency electromagnetic wave transmission,the interaction model between femtosecond laser plasma filaments array and radio frequency electromagnetic wave is established.The simulation results show that if ?=0° and with S polarization,the reflectivity increases slowly with the increase of electromagnetic wave incident angle.When the incident angle ? exceeds 45°,the reflectivity increases rapidly and reaches the maximum when approaching 90°.On the contrary,under the condition of ?=90° and P polarization,the reflectivity gradually decreases with the increase of the incident angle of electromagnetic wave,and approaches zero when approaching 90°.The effect of increasing electromagnetic wave frequency on its reflectivity is not obvious.It can be seen that when ?=0°,S polarization or ?=90°,P polarization,when ?=0°,the electromagnetic wave frequency of the two polarizations increases from 8.5 GHz to 12 GHz,and the reflectivity only changes by 0.2%.When the frequency of electromagnetic wave is 10 GHz and the electron density of plasma filaments is 1017 cm-3,reducing the distance between plasma filaments is beneficial to improving the reflectivity of radio frequency electromagnetic wave.The effect of radio frequency electromagnetic wave incident on the femtosecond laser filaments array were further experimentally studied,with emphasis on the influence law of different electromagnetic wave incident angles and plasma filaments spacing on electromagnetic wave transmission.The experimental results are consistent with the numerical simulation results.That is,when ?=0° and S polarization occurs,the reflection and absorption coefficient of radio frequency electromagnetic wave increases with the increase of incident electromagnetic wave angle.When ?=90° and P polarization,the sum of reflectivity and absorptivity of radio frequency electromagnetic wave gradually decreases with the increase of incident angle.Increasing the plasma filaments spacing will lead to the reflection and absorption coefficient of radio frequency electromagnetic waves decreases.In this paper,a theoretical model of the interaction between femtosecond laser filaments array and radio frequency electromagnetic wave is established and corresponding experimental research is conducted.The influence of femtosecond laser filaments array on electromagnetic wave transmission under different experimental conditions is obtained,which provides technical support for femtosecond laser plasma filaments to conduct electromagnetic wave and radar detection,lays a theoretical foundation for the development of electronic countermeasure technology in the future,and has a wide range of potential application prospects.