Fig. 1. Schematic diagram of the experimental setup. P, polarizer; F1, fused silicon lens with f =1  m; PST, periscope system; F2, fused silicon lens with f =6  cm.

Fig. 2. (Color online) Typical spectra induced by the filamentation of linearly and circularly polarized femtosecond laser pulses in air.

Fig. 3. Peak position of the 337 nm signal as a function of input laser energy of (a) linearly and (b) circularly polarized laser pulses. The solid lines are linear fits to the experimental results.

Fig. 4. Critical powers measured with different pump laser polarizations. The horizontal axis represents the rotation angle of the QWP.

Fig. 5. (Color online) Spatial evolution of (a)–(c) 391 nm and (d)–(f) 337 nm produced by linearly and circularly polarized laser pulses with the laser energy of (a) and (d) 0.7 mJ, (b) and (e) 1.2 mJ, and (c) and (f) 1.8 mJ. The focal length is f = 1  m.