Three-halves harmonic emission from femtosecond laser produced plasmas

Abstract

Measurements of three-halves harmonic radiation (3 0 /2) produced by femtosecond, Ti:sapphire laser pulses (р2ϫ10 17 W/cm 2 ) in long density scale length plasmas generated from solid aluminum targets are presented. The 3 0 /2 emission yield shows excellent agreement with theories of the two-plasmon decay instability in the predominantly linear regime.

General Properties of and 2w0 Harmonics Emission from Laser Driven Plasmas

“…The intensity of the light beam emitted in the 125° direction is almost double of that of the light beam emitted in the direction of 45°, while this later is narrower. This result is globally in agreement with some experimental results [12,16,17,19,20] , which in particular have demonstrated the existence of the twobeam structure for the References [12,20] have reported an angle of about 65°-70° for the forward beam and an angle of about 110°-120° for the backward beam, while reference [17] has obtained the maximum forward at 37° and the backward maximum at 153°, with respect to the laser incidence. They also have found that the angular distribution is also subject to the variation of the experimental parameters such as pulse-prepulse time delay and plasma scale length.…”

“…The backward beam of the 2 0 emission has been reported by several experimental works, but, to the best of our knowledge, its forward beam has not been measured or reported before. Its disappearance in the measured spectrum is may be caused by the spatial effects, as reference [20] has pointed out. Conversion efficiency of the order of 6×10 −4 was obtained for the 2 0 emission.…”

“…2 shows a two wings structure around the value 610 nm which corresponds to the wavelength of the exact frequency 2 0 ω , for the emitted of the Ion-Acoustic decay. Several experimental works [15][16][17][18][19][20] have obtained the two-wing structure of the emission. As it can be seen from the angular distribution, the emitted intensity is concentrated around two directions.…”

“…The first one is the process known as the oscillating mirrors (OM) [19,20] in which the intense laser field drives a relativistic oscillation of plasma surface, which causes a periodic phase modulation of the reflected light and, hence, the emission of harmonics of the laser frequency. The second one is the process called by Quéré et al [11] the coherent wake emission (CWE), in which this emission can be driven by the electron plasma waves generated around the critical density by the ponderomotive force of a laser pulse.…”

“…This kind of light emissions occur when an intense laser pulse is focused into a gas [8][9][10] or solid [11,12] through different processes. The of the plasma and near the critical density region, respectively [15][16][17][18][19][20] . While the emission of higher order harmonics or the so-called High Harmonic Generation (HHG) is according to Quéré et al [11] , du to two different processes.…”