Threshold for Three-Halves-Harmonic Generation in Relativistic-Laser-Produced Plasmas

We present an experimental investigation of three-halves-harmonic generation [1,2] in relativistic laser—plasma interactions at the quarter-critical-density surface. We analyze the three-halves harmonic energy and spectrum as a function of laser intensity, electron temperature, and plasma gradient scale length, which have been predicted to determine the two-plasmon-decay onset [3]. We explore discrepancies between the predicted and observed thresholds for three-halves-harmonic generation.

[1] L. Veisz, et al., Physics of Plasmas, vol. 11, no. 6, pp. 3311–3323, (2004)

[2] P. K. Singh, et al., Physics of Plasmas, vol. 22, no. 11, p. 113114, (2015)

[3] C. S. Liu and M. N. Rosenbluth, The Physics of Fluids, vol. 19, no. 7, pp. 967–971, (1976).