Linear conversion theory on the second harmonic emission from a plasma filament

The linear conversion theory of laser produced plasma filaments is studied. By calculations for the energy flux of the second harmonic emission on the basis of the planar wave-plasma interaction model, it has been found that there exists no 2ω0 harmonic emission in the direction perpendicular to the incident laser, in contradiction with the experiments. A linear conversion theory is proposed on the second harmonic emission from a plasma filament and discovered the intense 2ω0 harmonic emission in the direction perpendicular to the incident laser, which is in agreement with the experiments. (author)