# Efficient Multifocal Structured Illumination Microscopy Utilizing a Spatial Light Modulator
## 4 Discussion and Conclusions  
In this paper, a novel MSIM system for super-resolution microscopy with good performance is implemented in detail. With our system, a super-resolution image can be recovered just using nine raw multifocal images, realizing nearly a 1.5-fold enhancement in spatial resolution. This system is convenient to build up as we just add only an SLM to conventional WF microscopy, as well as quiet, stable, without moving parts in the illumination path. The utilization efficiency of the incident laser is critical for high-power imaging, especially for nonlinear imaging. The SLM here utilized for generating multifocal illumination patterns proved more efficient than the DMD, for the four diffraction laser beams hold around 42% power of the incident laser which could be reasonably accepted. We believe that this system may find potential application in the field of super-resolution microscopy.  
The absolute resolution enhancement reported here is lower than that in theory, which we attribute to two factors. First, achieving the highest possible resolution relies on obtaining diffraction-limited WF performance before MSIM is applied. Although we attempted this, the actual resolution is still not equal to the theoretical prediction (1.417 \(\upmu\)m) because of the undersized aberration caused by the optical elements. Second, the frequency of the illumination pattern is not close enough to the cut-off frequency of the WF microscopy owing to the current configurations which might be the main cause. The system reported in Reference [23] utilizes two separate interferometers with an individual delay line to generate and modulate the illumination pattern on the sample plane. From this point of view, our system provides the advantage of more simplicity over it and may have the great applicable potential in fast-scanning imaging.  
One of the major speed limitations of our MSIM system is the relatively low frame rate of the SLM (60 Hz). Due to the requirement of nine raw multifocal images for reconstruction, the maximum movement frequency of the sample is limited to 6.7 Hz, which is hard to meet the demand of imaging the moving sample with higher frequency. An alternative approach to alleviate this situation is to change the SLM with a higher frame rate or add 2D scanning mirrors in the optical path. The other limitation is the relatively low frame rate of the camera used. Increasing the camera frame rate invariably results in an increase in read noise and decrease in sensitivity, and the speed of a system is ultimately limited by the signal-to-noise level of the image. A path that we have taken in this system is to optimize its configurations to ensure the camera possesses a considerable sensitivity of detection at high speed.  
Conceptualization, W.L.; data curation, L.F., X.S. and S.W.; formal analysis, L.F., X.W. and W.L.; funding acquisition, W.L.; investigation, L.F., X.S. and S.W.; software, L.F., X.S. and S.W.; supervision, W.L.; writing--original draft, L.F.; writing--review and editing, X.W., L.L., O.K. and W.L. All authors have read and agreed to the published version of the manuscript.  
This work is financially supported by the National Key Research and Development Program of China (2018 YFB0504400); Tianjin Research Program of Application Foundation and Advanced Technology of China (19 JCYB)C16800); Fundamental Research Funds for the Central Universities; Tianjin Special Program for Talent  
Figure 9: Results of the fixed transverse section of esophagus (esophageal fibrous membrane) by WF microscopy **(a)** and MSIM **(b)**. **(c)** Intensity profiles along the colored dash lines in **(a,b)**, respectively. Scale bars: 40 \(\upmu\)m.  
Development; Open Research Funds of the State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM), 111 Project (B16027); [PERSON] thanks RFBR grant N18-52-16020.  
The authors declare no conflict of interest.