Applications of ghost imaging are limited by the requirement on a large number of samplings. Based on the observation that the edge area contains more information thus requiring a larger number of samplings, we propose a feedback ghost imaging strategy to reduce the number of required samplings. The field of view is gradually concentrated onto the edge area, with the size of illumination speckles getting smaller. Experimentally, images of high quality and resolution are successfully reconstructed with much fewer samplings and linear algorithm.

Stimulated emission depletion (STED) microscopy is one of far-field optical microscopy techniques that can provide sub-diffraction spatial resolution. The spatial resolution of the STED microscopy is determined by the specially engineered beam profile of the depletion beam and its power. However, the beam profile of the depletion beam may be distorted due to aberrations of optical systems and inhomogeneity of a specimen’s optical properties, resulting in a compromised spatial resolution. The situation gets deteriorated when thick samples are imaged. In the worst case, the severe distortion of the depletion beam profile may cause complete loss of the super-resolution effect no matter how much depletion power is applied to specimens. Previously several adaptive optics approaches have been explored to compensate aberrations of systems and specimens. However, it is difficult to correct the complicated high-order optical aberrations of specimens. In this report, we demonstrate that the complicated distorted wavefront from a thick phantom sample can be measured by using the coherent optical adaptive technique. The full correction can effectively maintain and improve spatial resolution in imaging thick samples.

For decreasing light loss and diminishing the aberrations of the optical system, an open-loop adaptive optics (AO) system for retinal imaging in vivo is introduced. Taking advantage of the ability of young human eyes to accommodate, there was only one single curved mirror to make the pupil of the eye conjugate with the wavefront corrector and the wavefront sensor. A liquid crystal spatial light modulator (LC-SLM) was adopted as the wavefront corrector because the LC-SLM can be made in a small size to match the sensor. To reduce a pair of lenses or focusing mirrors, the wavefront corrector and sensor are positioned in the noncommon path. The system adopts open-loop control and the high-precision LC-SLM guarantees the effectiveness of the AO system. The designed field of view is 1° on the retina (about 300 μm). The image quality was simulated with different mirror surface types, including circular, parabolic, and hyperbolic. A hyperbolic mirror with conic constant -1.07, which is close to -1, could best eliminate the aberrations. Theoretical analysis showed that the optical throughput of this system was at least 22.4% higher than that of a standard transmission AO system. In a practical experiment, a parabolic mirror was positioned in the optical path. Images of the cone photoreceptors and the capillary vessels were obtained successfully. This system simplifies the optical setup in comparison to the commonly used 4F systems while still guaranteeing the effectiveness of AO to correct the ocular aberrations.