Sub-diffraction resolution of periodic grating structures in a focus engineered sum frequency generation microscope

Use of Toraldo-type pupil phase masks in a nonlinear sum frequency generation microscope for subdiffraction resolution improvement is simulated. It is found that optimally chosen 0-w phase mask of diameter 64% of the full aperture results in reduction in the nonlinear focal field by 60% of the no phase mask case with 75% of energy concentrated in the central lobe. When imaging periodic grating structures, resonant enhancement and reversal of contrast are observed for grating pitch comparable to the diameter of the side lobes. The resonant contrast enhancement can potentially be used for selectively amplifying certain spatial frequencies in the sample.