Fig. 1. Extreme ultraviolet pulse generation. (a) Experimental setup; (b) spatial distribution of high-order harmonic spectrum; (c) high-order harmonic spectrum

Fig. 2. Generation of the 61st and 59th order harmonics in Ne varies with the driving laser energy and gas pressure (negative position indicates that the gas box is located behind the focal point, and the data has been interpolated). (a)(b) Harmonic generated as a function of driving laser energy (61st); (c)(d) harmonic generated as a function of gas pressure (61st); (e)(f) harmonic generated as a function of driving laser energy (59th); (g)(h) harmonic generated as a function of gas pressure (59th)

Fig. 3. Spatial distributions of high-order harmonics. (a) High-order harmonic spectrum (focal position is 0); (b)(c) spatial profiles of 61st and 59th order harmonics corresponding to Fig. 3(a); (d) high-order harmonic spectrum (focal position is -100 mm); (e)(f) spatial profiles of 61st and 59th order harmonics corresponding to Fig. 3(d); (g) high-order harmonic spectrum (focal position is -160 mm); (g)(i) spatial profiles of 61st and 59th order harmonics corresponding to Fig. 3(g)