Design of a Multipoint Scanning Microscope Using Cascaded Flexible Gratings
Objective Laser scanning microscopes use lasers as light sources to obtain high-resolution and high-contrast images of samples through point-by-point scanning. This method is characterized by non-contact,high efficiency,accuracy,dynamic analysis,and fast scanning speed,making it widely used in neuroscience,chemical raw materials,materials science,and biology research. Recent advancements in multipoint scanning microscope technology aim to improve both scanning speed and imaging resolution. Typically,scanning—whether single-point or multi-point—relies on controlling the motion of a motorized platform. However,the bulky and complex nature of these platforms results in poor dynamic performance. Flexible gratings,made from polymers such as polydimethylsiloxane (PDMS) and polymethyl methacrylate (PMMA),offer advantages including small size,high toughness,transparency,and ease of preparation. In this study,we propose a concept for a 1550 nm multipoint scanning microscope system utilizing two cascaded flexible gratings and construct its theoretical model. The theoretical feasibility of the system is verified through simulations of the illumination and emission light paths using ZEMAX software. We hope this method provides a new approach for efficient multipoint laser scanning.Methods In this study,two flexible gratings with perpendicular grating directions are used as scanning structures. We first develop a theoretical model and derive the corresponding formulas,which are then simulated using MATLAB to analyze factors affecting diffraction spot position changes. To further reduce spherical and other aberrations,we design objective lenses consisting of multiple lenses using ZEMAX and incorporate them into subsequent simulations of illumination and emission light paths. For the emission light path,the sample surface is modeled as a mirror,with reflected light serving as the light source. A multi-configuration editor is used to match the diffraction orders of the beam before and after passing through the cascaded flexible gratings. Finally,the simulation results are compared with previous work.Results and Discussions Numerical simulations reveal that the diffraction spot position changes linearly during the stretching of flexible gratings 1 and 2,with spots approaching the y and z axes. When flexible grating 1 is stretched,the (±1st,±1st) spots move along both the y-axis and z-axis simultaneously (Fig. 3). If the distance L2 between grating 2 and the screen is sufficiently small,the z-axis movement is negligible during point scanning. In addition,less force is required at 1550 nm compared to 650 nm and 1064 nm for the same diffraction spot displacement (Figs. 2 and 3). Therefore,cascaded flexible gratings are suitable for laser scanning,with 1550 nm light sources being particularly effective. The designed objective parameters are listed in Table 2. In the simulation,the LONA and SPHA operands are used to control axial and spherical aberrations of the objective lens,while the EFFL operands control the total focal length,which is optimized to 6 mm. The objective lens exhibits less than 1 μm spherical aberration[Fig. 7(b)],with a numerical aperture (NA) of 0.611 and a resolution of approximately 1.547 μm. The modulation transfer function (MTF) value exceeds 0.1 at a spatial frequency of N=704 lp/mm[Fig. 7(d)]. In the illumination light path simulation,the light source is a Gaussian beam with an apodization factor of 1.0,a wavelength of 1550 nm,and an NA of 0.14. The spherical aberration is less than 1 μm[Fig. 8(b)],and the scanning area formed by diffraction spots is 23.4 μm×23.4 μm (Fig. 9). The MTF curves for the nine diffraction spots exhibit minimal variation,with MTF values greater than 0.1 at a spatial frequency N=701 lp/mm (Fig. 10). In the emission light path simulation,the receiving lens group 5,composed of multiple lenses (Table 3),shows overlapping diffractive beams on the receiving end surface[Fig. 11(c)],with spherical aberration less than 1 μm[Fig. 11(d)]. The MTF value of nine diffraction spots exceeds 0.1 at a spatial frequency of N=464 lp/mm (Fig. 11).Conclusions We propose a 1550 nm multipoint scanning microscope system using two cascaded flexible gratings and construct a theoretical model. The system achieves simultaneous scanning of the sample using (±1st,±1st) diffraction spots through the stretching of cascaded flexible gratings. ZEMAX simulations of the illumination and emission light paths confirm the theoretical feasibility of the system. The simulation results indicate that the scanning area of the system is 23.4 μm×23.4 μm. MTF data for the nine diffraction orders are greater than 0.1 at the spatial frequencies of N=701 lp/mm in the illumination light path and N=464 lp/mm in the emission path. Our study demonstrates the theoretical feasibility of the multipoint scanning microscope with cascaded flexible gratings and its potential for achieving effective imaging.
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