Effect of polarization in evanescent wave amplification for the enhancement of scattering of nanoparticles on surfaces

Abstract

We demonstrate the far field detection of low-contrast nanoparticles on surfaces using a technique that is based on evanescent-wave amplification due to a thin dielectric layer that is deposited on the substrate. This research builds upon earlier results where scattering enhancement of 200 nm polystyrene (PSL) particles on top of a glass substrate covered with a ≈ 20 nm InSb layer has been observed by Roy et al. [Phys. Rev. A 96, 013814 (2017)10.1103/PhysRevA.96.013814]. In this paper, the enhancement effect is analyzed using other dielectric materials with lower absorption than the previous one, resulting in a higher signal-to-noise ratio (SNR) for particle detection. We also consider several polarizations of the incoming field, such as linear, circular, azimuthal, and radial. In our experiments, we observe that the optimum enhancement occurs when linear polarization is used. With this new scheme, PSL nanoparticles of 40 nm in diameter have been detected at a wavelength of 405 nm.

Label-Free Imaging of Subwavelength SiO2 Nanoparticle Arrays Using Evanescent Wave-Assisted Dark-Field Microscopy

“…By using the Fresnel equation, the reflection or transmission coefficients of the incident light can be expressed as 11,27 For the plane waves with given k x incident on a silver film (d = 50 nm), the wave vector component of the transmitted wave…”

“…By using the Fresnel equation, the reflection or transmission coefficients of the incident light can be expressed as , r s = k z 1 − k z 2 k z 1 + k z 2 ; r p = n 2 2 k z 1 − n 1 2 k z 2 n 2 2 k z 1 + n 1 2 k z 2 t s = 2 k z 1 k z 1 + k z 2 ; t p = 2 n 2 2 k z 1 n 2 2 k z 1 + n 1 …”

“…By using the Fresnel equation, the reflection or transmission coefficients of the incident light can be expressed as , …”

“…Using evanescent fields to illuminate samples can also shift the high-frequency information of samples to low frequency and improve the imaging resolution. In addition, researchers have demonstrated that the scattering signal of nanoparticles on a substrate coated with a high refractive index dielectric film is increased by enhancing the evanescent waves, 10,11 which can increase the contrast and sensitivity in imaging. Plasmonic scattering microscopy collects the signal scattered by a sample and the background signal generated by SPP, and a better sensitivity is achieved in label-free single-molecule imaging.…”

“…Using evanescent fields to illuminate samples can also shift the high-frequency information of samples to low frequency and improve the imaging resolution. In addition, researchers have demonstrated that the scattering signal of nanoparticles on a substrate coated with a high refractive index dielectric film is increased by enhancing the evanescent waves, , which can increase the contrast and sensitivity in imaging. Plasmonic scattering microscopy collects the signal scattered by a sample and the background signal generated by SPP, and a better sensitivity is achieved in label-free single-molecule imaging. − In addition, theoretical results show that when evanescent waves illuminate a sample, the far-field scattering direction of the sample can be adjusted by changing the polarization (such as radial polarization, S polarization, and P polarization) of the evanescent waves, which can improve the resolution.…”