Fig. 1. (a) Schematic of tight focusing using a parabolic mirror and a hyperbolic mirror. Illustration and comparison of secondary focusing using (b) hyperbolic and (c) ellipsoidal mirrors. 2Δα and 2Δα′ are input and output angular apertures, respectively.

Fig. 2. Variations of (a) magnification ratio Δα′/Δα and (b) output angular aperture 2Δα′ with eccentricity c/a for different input angular apertures 2Δα=10deg, 20 deg, and 30 deg and a fixed edge angle αe=5deg.

Fig. 3. When the angular apertures are (a)–(c) 20 deg and (d)–(f) 84.3 deg, (a) and (d) spatial intensity distribution in the focal region for the λ=800nm laser center wavelength, and (b) and (e) spatiospectral and (c) and (f) spatiotemporal intensity distributions in the geometrical focal plane z′=0 for a 60 nm FWHM bandwidth Gaussian-pulsed beam. Curves are on-axis profiles.

Fig. 4. When the angular aperture is 84.3 deg, spatial (a) electric-field and (b) intensity distributions in the focal region for 1200, 900, and 600 nm wavelengths, and (c) spatiospectral, spatiotemporal (d) intensity and (e) electric-field distributions in the geometrical focal plane z′=0 for a 600 nm FWHM bandwidth 12-order super-Gaussian pulsed beam. Curves are on-axis profiles.

Table 1. Optimal focusing conditions for different input angular apertures.*