A. Tarasevitch et al., Generation of high-order spatially coherent harmonics from solid targets by femtosecond laser pulses - art. no. 023816, PHYS REV A, 6202(2), 2000, pp. 3816
This paper discusses the generation of high-order optical harmonics from so
lid targets using laser pulses of 35 and 120 femtoseconds. Harmonics up to
the 35th order were observed. High conversion efficiency has been achieved,
e.g., 10(-6) to the 10th harmonic. It is demonstrated that the harmonic em
ission is highly directional and that the harmonic efficiency decreases rap
idly with increasing plasma scale length.