Research Of Confocal Scanning Method Based On Phase-only Liquid Crystal Spatial Light Modulator

Confocal microscopy has been widely used in biomedicine, materials science,industrial testing and other areas for its unique optical sectioning property, high lateralresolution performance and nondestructive detection. Since confocal microscopy takes3D detection point-by-point, which can only get the information at one spot a time,3Dscanning becomes necessary in the process of confocal3D measurement. The traditionalmethods of confocal scanning are mechanical means of which the characteristics ormechanical driving technology limitations could not meet the requirements of live cellimaging and other application areas.Aiming at the shortcomings of mechanical scanning methods, non-mechanicalscanning methodis proposed. This paper titled"Confocal Scanning System Based OnPhase-only Liquid Crystal Spatial Light Modulator " utilizes a phase-only liquid crystalspatial light modulator to achieve3D scanning in confocal microscopy. A lateraldisplacement of the beam focus can be attained if the hologram is chosen tobe a blazedgrating. By adding a lens term to the blazed gratings, the beam focus can be shifted upand down parallel to the optical axis.Five aspects of theoretical analysis and experiments have been carried out:Firstly, by using a prism phase distribution delay, the phase-only liquid crystalspatial light modulator can achieve uniform, continuous deflection of single beam.Andthe maximum deflection angle, the efficiency of the deflection angle and theprecision of deflection angle has been analyzed based on the model of the beamdeflection.Secondly, with a phase distribution delay of a Fresnel lens, the phase-only liquidcrystal spatial light modulator can achieve a shift of beam focus parallel to the opticalaxis. The shifting range of the beam focus and the scanning accuracy has been analyzedbased on the analysis and simulation of characteristics for Fresnel lens.Thirdly, by using Prism-Lens phase distribution delay method, the phase-onlyliquid crystal spatial light modulator can achieve the beam focus spot position control inthree-dimension space. Moreover, the range of focal spot movement and positioningaccuracy has been analysised.Then, based on the technology of beam focus position control in three-dimension space with a phase-only liquid crystal spatial light modulator, this paper has designed aconfocal scanning system. In the lateral direction, a prism phase distribution delay wasdisplayed to realize fast beam scanning. In the axial direction, a Fresnel lens phasedistribution was displayed to achieve focus shifted up and down parallel to the opticalaxis. This scanning system can produce a fast non-mechanical3D scanning for confocalmicroscopy. This beam scanning system can improve the3D imaging speedsignificantly. This paper also analysises the scanning range and positioning errors of thisscanning system.Finally, a testing system for relevant experiments has been set up, and the errors ofmeasurement results have been anylyzed. The availibility of non-mechanical3Dscanning for confocal microscopy has been proved by achieving the axial responsecurve of the tested confocal system which is compared with the axial response curve ofthe system using conventional mechanical scanning.