A fast noninvasive method based on scattering from a focused radially polarized light to detect and localize subwavelength nanoparticles on a substrate is presented. The technique relies on polarization matching in the far field between scattered and spurious reflected fields. Results show a localization uncertainty of ≈ 10 −4 λ 2 is possible for a particle of area ≈λ 2 =16. The effect of simple pupil shaping is also shown.
Spot size reduction is demonstrated by printing focused spots from amplitude-modulated radially polarized light at the wavelength λ = 405 nm on a photoresist. Amplitude modulation is realized by ring illumination and by application of an optimized amplitude distribution function. Amplitude modulation is implemented via spatial light modulator, which is followed by a specially designed radial wire grid polarizer to obtain high-quality radially polarized light. Comparison between full and amplitude modulated apertures of the written focused spots on a photoresist is performed. Rigorous simulations based on the Richards-Wolf integral are made to confirm experimental data.
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