* * * focusing technology mainly introduces pinholes in the optical path. Pinhole can effectively control the depth of focus and prevent the interference of impurity signals. I think the question should be too ideal for the subject, just as the subject said, "But the focus of * * * is time scanning, that is to say, I first observe Airy spot A, and when I scan to the next place, it corresponds to Airy spot B"; Maybe the actual measurement process is not necessarily from Airy spot A to Airy spot B by scanning, so it is very likely that these two Airy spots basically coincide. For example, the simplified schematic diagram of the principle of focusing microscope in the following figure shows that we only want to image the focus (in fact, * * * focusing is to record the light intensity information point by point, and finally process it into a two-dimensional or three-dimensional "image"), but this is a pure ideal state and cannot be just. In addition, this small displacement has high requirements for the translation table.

* * * Focusing microscope is a kind of scanning microscope.

All scanning microscopes can be regarded as detecting objects pixel by pixel with a probe, and then splicing them into an image.

The scanning step size can be infinitely small, but the resolution is limited by the probe tip size. The needle tip is too thick, even if the scanning distance is as small as Planck length, it will not help to improve the resolution because the pixels overlap.

* * * The tip size of a focusing microscope is the optical diffraction resolution λ/NA.

According to Nyquist sampling law, the scanning interval is less than 1/2 times of diffraction resolution.

Ordinary * * * focal microscope is impossible unless it is STED's super-resolution imaging technology. * * * Compared with ordinary wide-field microscopic imaging, focal microscopic imaging has limited lateral resolution and cannot break through the diffraction limit. The horizontal scanning interval of 1nm only improves the spatial sampling frequency, but does not improve the horizontal resolution.