Research On The Application Of Secondary Twisted Grating In Microscopic Imaging

Quadratic distorted(QD)grating is acted as a multi-focal lens,which can generate different diffraction orders with different focal lengths.To date,the QD grating has been widely applied in virtue of the property,such as multi-plane imaging,flow velocimetry,particle tracking and so on.Traditional methods need to scan at different vertical positions to get the distribution of the micro-objects in a 3D volume,while the multi-plane imaging technique based on the QD grating can imaging multi-plane of the object simultaneously via a single record of a charge coupled device(CCD).It has high real-time and high efficiency in practice.Starting from theoretical analysis,this paper studies the optimal design of the QD grating and its application in particle velocity measurement and multi-particle phase correction.Firstly,the imaging principle of the QD grating is analyzed theoretically.The main issues discussed in this section are that,the effect on magnification of imaging system when the QD grating and a lens combined with different distance.We theoretically and experimental demonstrated the magnification of each imaging plane is equivalent,when the distance between QD grating and a lens is equal to the focal length of the lens.This characteristic makes it more suitable for multi-plane imaging.Secondary,we propose a simultaneous imaging at unequal interval distance based on the QD grating.The method of realizing simultaneous imaging with unequal interval is analyzed theoretically,and the formula of the distance of different layer is deduced.The imaging system combine the QD grating and polarization multiplex technique in which a Liquid Crystal spatial light modulator(SLM)is divided into two panels with equal area,and imprinted two QD grating with different pattern direction,which generate horizontal and vertical diffraction orders,respectively.The diffraction beam is separated into two optical channels with mutually orthogonal polarization state,as the incident light of SLM.We realized the imaging of multiple unequal-distance-object layers by adjusting the parameter of the two QD gratings.In experiment,we use two size samples includes statics letter slices and yeasts to prove the practicability of our system.The yeasts are needed to magnify by microscopic system,while the statics letter slices can use the imaging lens to realize the multi-plane imaging directly.Afterwards,the yeasts are leaded into a microfluidic tube as a dynamic sample,we further verify the technique successfully,the strong real-time performance of the system is demonstrated,and the moving velocity of the particles is calculated.At the same time,to imaging the unequal-distance-object layers which is convenient and flexibility,we design a new grating which is based on the blazing QD grating and a multi-zone plate composed of many fan-shaped subareas which accordingly generate lateral position controllable multifocal spots.Finally,we compared the imaging quality of this scheme under illumination light sources of different structure,include Gaussian beam and Bessel beam.The distribution of intensity and propagation process of the Bessel beam is shown by numerical simulation.And the property of Bessel beam such as the non-diffraction and self-repairing are analyzed in detail.The optical experiment results are also illustrated.Compared with the Gaussian beam as the illumination light source,the Bessel beam can reduce the noise of background clearly.Furthermore,due to the microfluidic tube causes an additional phase,the phase of imaging sample have a certain degree of deformation.Thus,we utilize the digital holography to restore the phase of a deformed sample and the microfluidic tube.And then we recover the correct phase of the sample via the subtraction of phase.