Multifrequency parallelized near-field optical imaging with anistropic metal-dielectric stacks

Metal-dielectric stacks can be designed to support resonant transmission modes for certain evanescent field components of an incident electromagnetic field. Here we show that when combined with an appropriate subwavelength pitch grating the amplified Fourier components coincide with different diffraction orders at different frequencies. It thereby becomes possible to collect a wide range of evanescent Fourier components by performing measurements at different optical frequencies. For a typical anisotropic metal-dielectric stack, we find that for a source emitting at wavelengths 400–500 nm, imaging with a resolution of ≈20 nm becomes possible. Although the reconstructed image contains ringing effects due to gaps in the measured Fourier spectrum, the final resolution achievable is a significant improvement over other fast near-field imaging techniques. The presented technique may find applications in fast super-resolution surface imaging of objects that emit over a wider optical frequency range.