Fig. 1. Experimental setup. The inset shows a typical picture of a filament-drilled pinhole.

Fig. 2. (a) Side fluorescence images of filaments in LP and CP with f = 30 cm focusing lens. The images were accumulated for 40 shots. (b) The diameters of the laser filament-drilled (f = 30 cm) Al foil pinholes as a function of the number of the laser shots. The laser energy was 1 mJ. (c) Measured laser fluence distribution along the LP or CP filaments (f = 30 cm). The solid curves are polynomial fits as a guide for the eye. The radius of the pinhole was approximately 42.3 µm. The position “0” corresponds to the geometry focus (f = 30 cm), while the positive values indicate the positions prior to the geometry focus. (d) Measured laser fluence with f = 30 cm focusing lens as a function of the input laser energy at LP (ellipticity of zero). (e) Clamping laser fluence inside the filament core versus different initial laser polarization ellipticities under the external focusing conditions of f = 30 cm and f = 100 cm, respectively. (f) Laser spectra measured after filamentation.

Fig. 3. (a) Peak intensity as a function of propagation distances. The focal length is 30 cm unless it is stated. (b) Laser energy confined in the range of r<42.1μm as a function of propagation distance. (c) The beam sizes (fluence at FWHM) as a function of propagation distances. The vertical dot line indicates the propagation distance (z=0.57cm), where the maximum intensity during the propagation is obtained in the CP case. In the LP case, the maximum intensity is obtained at z=0.59cm. (d) Simulated clamping intensity versus the initial laser polarization ellipticity under external focusing conditions of f=30cm, 50 cm, and 100 cm, respectively.