Lateral resolution enhancement with standing evanescent waves

Abstract

A high-resolution fluorescence microscopy technique has been developed that achieves a lateral resolution of better than one sixth of the emission wavelength (FWHM). By use of a total-internal-reflection geometry, standing evanescent waves are generated that spatially modulate the excitation of the sample. An enhanced two-dimensional image is formed from a weighted sum of images taken at different phases and directions of the standing wave. The performance of such a system is examined through theoretical calculations of both the point-spread function and the optical transfer function.

Fig. 1

For the representative parameters of N = 4, θ_i = 75°, NA = 1.3, λ = 532 nm, and λ_e = 560 nm, plots are generated that show (a) the PSF’s of conventional, confocal, and SWTIRF microscopies, (b) the PSF of a one-dimensional (1D) SWTIRF (quartz, n = 1.46) scan [Eq. (10)], (c) the symmetric PSF of two-dimensional (2D) SWTIRF (quartz) generated by Eq. (14).

Fig. 2

(a) and (b), Frequency space counterparts (OTF’s) of Figs. 1(b) and 1(c), respectively.