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. $2\mathrm{\Delta }\alpha$ and $2\mathrm{\Delta }{\alpha }^{\prime }$ are input and output angular apertures, respectively.

Fig. 2. Variations of (a) magnification ratio $\mathrm{\Delta }{\alpha }^{\prime }/\mathrm{\Delta }\alpha$ and (b) output angular aperture $2\mathrm{\Delta }{\alpha }^{\prime }$ with eccentricity $c/a$ for different input angular apertures $2\mathrm{\Delta }\alpha =10\mathrm{deg}$, 20 deg, and 30 deg and a fixed edge angle ${\alpha }_e=5\mathrm{deg}$.

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 $\lambda =800\mathrm{nm}$ laser center wavelength, and (b) and (e) spatiospectral and (c) and (f) spatiotemporal intensity distributions in the geometrical focal plane $z^{\prime }=0$ 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 $z^{\prime }=0$ 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.*