Density modulation produced by ultrashort laser pulses and the phase reflection induced in underdense plasmas
激光脉冲诱导的等离子体密度调制及其产生的相位反射

It is shown theoretically and by particle-in-cell simulations that the interfering fields of the incident and reflected laser pulses can produce deep plasma density modulations in underdense pre-plasmas. This occurs within a few tens of laser cycles if the incident laser pulse is at moderate intensities such as 10^15W/cm^2. Such density modulations can serve as a Bragg reflector, which results in phase reflection from underdense plasmas. Because the deep density modulations are just a period of half a wavelength in the plasma,the reflected wave reaches the maximum by resonance with a reflectivity up to near 100% .The phase reflection can also be observed from the plasma with a linear density profile, which can significantly reduce the laser absorption by fusion targets.