Study On Compact Soft X-Ray Microscopy And The Method Of Extending The Depth Of Focus

Because of the adoption of soft X-rays in the water window(2.3-4.4 nm),the soft X-ray microscopy imaging system has a unique advantage in the nano-scale high-contrast imaging of living cells in the natural state,Which is a key tool to observe the true ultrastructure in cells.The three-dimensional soft X-ray microscopy imaging combines the X-ray microscopy imaging technique with traditional tomography(CT)technique,achieving high resolution imaging of living cells through soft X-ray microscopy technique based on devices such as multilayer mirrors and Fresnel zone plates,and reconstructing the three-dimensional structure of the sample through traditional CT tomography based on multi-angle projection.At present,soft X-ray microscopy mostly adopt synchronous radiation sources.which must use large synchrotrons.The imaging device must be built in a place with synchrotron radiation facilities,which has high construction cost and construction complexity.The availability of light sources has been greatly restricted,which greatly limits the popularity of this technology.In recent years,with the continuous development of compact soft X-ray source technology and the continuous improvement of light source performance,compact soft X-ray source based on laser plasma has been used more and more.This kind of light source has small volume and cost.The advantages of small size,low cost and easy access provide strong support for the development of miniaturized soft X-ray microscopy imaging technology.In this paper,an implementation scheme of a compact soft X-ray source based on laser plasma is proposed for a soft X-ray microscopy imaging system.It can provide soft X-rays with low debris,stability,high strength,easy adjustment and low cost for imaging of aqueous samples.As the objective lens in the soft X-ray imaging system,the zone plate is a key component of the system,which uses X-ray diffraction to enlarge the biological sample.The imaging model of the zone plate is very important for the study of the whole system imaging model.In this paper,the angular spectrum analysis method is used to simulate the imaging model of the zone plate,Utilize the circular symmetry of the Fresnel zone plate to reduce the calculation load,and finally obtains the angle spectrum of the Fresnel zone plate and the point spread function(PSF)under different defocus planes,which helps to further understand the imaging model of the system and provides theoretical support for the study of the depth of focus expansion algorithm of the imaging system.For a soft X-ray microscopy imaging system with a certain depth of focus(DOF),since the zone plate has a certain depth of focus when imaging,the imaging resolution of the reconstructed three-dimensional image is higher when the sample is in the depth of focus,and lower because of phenomenon of blurring due to defocusing when the sample is partially outside the depth of focus.In this paper,the method based on PSF deblurring and image stack fusion is used to expand the inherent depth of focus(DOF)of the imaging system,which can improve the observation range of the imaging system,so that samples with thickness greater than the depth of focus can be imaged without loss of resolution.Finally,this paper introduces the construction of a compact soft X-ray imaging experimental platform based on laser plasma source,the imaging system is currently under construction.The laser plasma source is the core component of the system and has been able to achieve long-term stable operation.In addition,a software for compact soft X-ray microscopy imaging system is designed,which can realize functions such as hardware control,data pre-processing,3D reconstruction,image post-processing,etc.,and provides user with a richly functional and interoperable software.