Fig. 1. Sketch of the spectrometer and monochromator with HHG.

Fig. 2. Part of the HHG spectrum of Ar atoms at 90 torr irradiated by a 800 nm, 35 fs linearly polarized and radially polarized driving laser field with laser energy of 1.0 mJ: (a) Part of the HHG spectrum produced by a Gaussian driving beam; (b) the corresponding integrated HHG intensity; (c) part of the HHG spectrum produced by a radially polarized driving beam; (d) the corresponding integrated HHG intensity. The x-order of the harmonics are labeled as Hx in the figure.

Fig. 3. Far-field intensity distributions of EUV light with the orders of 21st generated with Gaussian beam and radially polarized beam: (a) EUV generated by Gaussian beam; (b) EUV vortex generated by radially polarized beam.

Fig. 4. Far-field intensity distributions of EUV vortex generated with radially polarized beam and diameters of the EUV vortex rings.

Fig. 5. Yield of the modes as a function of the gas pressure and laser energy for the harmonic and vortex harmonic: (a) Harmonic with the orders of 19th; (b) harmonic with the orders of 23rd.