Research On Control System Of Laser Scanning Confocal Microscope

Laser scanning confocal microscope (LSCM) is an effective technical measureand essential scientific instrument to study sub-micron fine structure, which has beenwidely used in the field of biological and industrial detection. In addition, it is alsothe basis for further development of super-resolution imaging technology such asSTED. Control system is the key to ensure that LSCM functions properly. Thisdissertation studies and designs the control system of LSCM in a top-down approachaccording to the modular principle. The central control unit of the control system isbuilt by ARM and FPGA, which sends instructions to subsystems including scanningcontrol module, signal acquisition module and spectral imaging module.Two orthogonally placed scanning galvanometers are used in scanning controlmodule to implement two-dimensional scanning of sample plane. And voltagewaveforms that control galvanometers are generated using DDS technology. Acorrection approach for nonlinear distortion in scanning imaging process of LSCMusing arctangent waveform controlling galvanometer is proposed in this module, andformation of arctangent waveforms is implemented by ARM, FPGA and DACcircuits. Experiments show that the orthodox correction method using f-θ lens setcould be replaced by the approach of arctangent waveform controlling, whichreduces the cost of LSCM system.PMT is selected to detect the weak fluorescence signals in signal acquisitionmodule. And a system is designed to process the output of PMT, in which a switched integrator and sampling method is proposed, which integrates the output of PMT ineach pixel time and samples at the end of each pixel time. Experiments show that thesignal-to-noise ratio of image is improved and the imaging quality is enhancedsignificantly. Furthermore, a logic unit for signal synchronization is designed onFPGA to generate integral control signals, line sync signal, frame sync signal andsampling control signal, which achieves hardware synchronization of the signalacquisition module and the scanning control module.Each slit in the spectral imaging module is formed by two movable slit edges,which are separately installed on a stepping motor, so that width and position of slitcan be precisely set to select different fluorescence components by servo controlusing ARM which controls stepping motors according to negative feedbacksgenerated by encoder and optical coupler switch. Experiments show that thedesigned system is able to set the position of slit edges precisely and achieve imagesof different fluorescence components from the sample simultaneously, which extendsapplication area of LSCM.The designed control system has not only met the imaging requirements ofLSCM system, but also laid a solid foundation for the development of STEDmicroscopy.