Impacts of Grating Frequency on Super Resolution via Structured Illumination Microscopy

Besides the well-established limit of about 2 times beyond the diffraction limit, the super resolution imaging using structured illumination microscopy method also depends critically on the grating frequency used for the structured illumination patterns. The exact nature of this dependence was not well-understood. We systemically investigated the impacts of the grating frequency using numerical simulations and quantified the non-uniform spatial frequency responses of SIM and its impact on the SIM. We found that image targets with lower spatial frequencies below the diffraction limit can become unresolved depending on the relationship of the grating frequency used and the diffraction limit of the system. In addition, while the highest resolution enhancement achievable by increasing the grating frequency is about three times of the diffraction limits, using higher grating frequency would in fact deteriorate the resolution enhancement rapidly and eventually make the image resolution worse than the diffraction limit.