Unlike SMLM, the illumination profile in SIM is critical as the image is essentially the multiplication of the sinusoidal stripe pattern and the distribution of fluorophores in the target structure. Aberrations in the excitation beam path can distort and smear the illumination pattern, thereby reducing image contrast and resolution, introducing artifacts, and even causing complete failure of image reconstruction (Arigovindan
et al.
2012; Liu
et al.
2020). Therefore, aberration corrections are required in both illumination and detection beam paths, which can be performed simultaneously by using a single DM in the common beam path. Both direct and indirect wavefront sensing methods have been applied to SIM to correct for optical aberrations and improve image quality. Turcotte
et al. implemented a direct wavefront sensing module using multiphoton guide stars to facilitate super-resolution imaging of the brains in live zebrafish larvae and mice (Turcotte
et al.
2019). They observed the dynamics of dendrites and dendritic spines at nanoscale resolution with the help of AO to correct for sample-induced aberrations (
Fig. 4A). Similarly, Zheng
et al. used a nonlinear guide star in two-photon instant SIM (2P-ISIM) to measure optical aberrations in both excitation and emission baths and correct them by a DM (Zheng
et al.
2018). They demonstrated up to 40-fold intensity enhancement and substantial resolution recovery in cells and tissues at depths up to 250 μm (
Fig. 4B). Using an indirect wavefront sensing method, Debarre
et al. investigated the effect of different aberration modes on the illumination patterns in SIM and corrected for each mode independently using an image quality metric (Debarre
et al.
2008). Thomas
et al. introduced a phase retrieval approach to correct for aberrations in SIM, which improved the image contrast of fluorescent beads and achieved a resolution of 140 nm through 35 μm of tissue (Thomas
et al.
2015). Zurauskas
et al. reported a sensorless AO strategy based on image quality with improved sensitivity and reliability for aberration correction in 2D-SIM (Zurauskas
et al.
2019). They combined it with a customized illumination pattern to enhance the sampling of OTF, producing more isotropic and better overall correction results (
Fig. 4C). Lin
et al. further extended the sensorless approach to 3D-SIM to recover information severely distorted by optical aberrations and to restore image quality and resolution when imaging a variety of biological samples (
Fig. 4D) (Lin
et al.
2021).