Enhancing resolution of terahertz surface plasmon resonance microscopy by classical ghost imaging using free electron laser radiation

Abstract

Surface plasmon resonance (SPR) microscopy is one of the most sensitive label-free microscopy methods, however with low lateral resolution. This drawback is primarily caused by the fact that surface plasmon polaritons (SPPs) excited by terahertz (THz) radiation propagate macro distances (about ∼100 1) from their excitation spot, thereby blurring the observed region, like with a scattering medium. To eliminate this disadvantage, we adapt a method known as ghost imaging (GI), which is notable for its tolerance to environmental aberrations between the object and camera. We propose an optical scheme of SPR microscopy for the THz range with an additional optical arm to implement the classical GI and provide an analysis of factors affecting the image quality. To implement the classical GI in the THz range, we propose to use the Novosibirsk free electron laser (NovoFEL) as a THz radiation source. The high beam power of the NovoFEL provides a speckle structure with a pronounced profile, which is required to achieve a high level of contrast in the obtained image. Moreover, the large coherence length of the NovoFEL radiation is necessary to ensure a large degree of correlation between the beams emerging from the beam splitter, which allows reconstructing an image with a lower noise level.