Surface-plasmon-coupled emission microscopy with a spiral phase plate

Abstract

The surface plasmon-coupled emission microscope provides high sensitivity for surface imaging. However, it suffers from a distorted donut-shape point-spread function (PSF). Here we report an effective yet simple method to correct for the distortion by introducing a spiral phase plate. This modification converts the donut PSF into one that is single lobed, which is preferable for imaging. The optical performance of the system is characterized and compared with previous publications. This technique provides more than twofold lateral resolution enhancement.

Fig. 1

(Color online) Setup of modified SPCE microscopy using a high-NA TIRF objective, with an SPP inserted in the infinity-corrected optical path of the detection optics.

Fig. 2

Emission at the BFP of the objective at time instance t=0. (a) Polarization pattern of the electric field without the SPP and (b) changes in polarization when the SPP is inserted. The insets show that the intensity at the BFP remain the same.

Fig. 3

(Color online) (a) Comparison of the vectorial OTF of SPCEM without SPP (solid curve) and with SPP (dashed curve) (b) Characteristics of SPP errors: dip ratio I₀ (plus signs) and normalized FWHM (crosses) as a function of misalignment Δw; I₀ (circles) and FWHM (diamonds) as a function of wavelength mismatch Δλ/λ.

Fig. 4

Comparison between simulation and experimental results. Simulated PSF (a) without SPP and (b) with SPP; experimental PSF (c) without SPP and (d) with SPP. Image scale is 2 μm × 2 μm.