Multiphoton Excitation of Plasma Waves

Recently developed table-top laser sources are capable of producing intensities on target of 1017Wcm −2 in femtosecond pulses. This has stimulated interest in the possible mechanisms for laser light absorption in a plasma produced by such a source. The plasma, expanding at approximately the ion sound speed ( υ s = Z k B T e / m i ) , remains at virtually solid density during the pulse. Light incident on such an overdense plasma boundary will be largely reflected, unless there is strong absorption within the skin depth of the target (~ c/w p ), where the evanescent wave does penetrate.