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

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.