Technical Research Of Diffraction Barrier Breakthrough In Coherent Anti-stokes Raman Scattering Microscopy

The most excting recent applications of CARS have been in the fields of biologicaland medical imaging. Coherent anti-Stokes Raman scattering (CARS) microscopy is arecently developed nonlinear vibrational imaging technique for high-sensitivity,three-dimensional, and chemically selective imaging without exogenous labelingagents of lipids, especially lipids in live cells an organisms. The application of CARSmicroscopy is limited, nevertheless, by an acquirable lateral and axial spatialresolution, typically300nm and800nm. Accordingly, a remaining crucial problemfor CARS is how to breakthrough the diffraction and achieve resolution-enhancedimages.Based on the full quantum treatment of time-resolved CARS, we suggest anapproach, the so-called additional probebeam-induced phonon depletion (APIPD)method, to visualize the resolution enhancement of CARS microscopy and report atheoretical analysis of detection limit (DL) for it. We apply CARS to demonstratevibration imagings of polystyrene beads spin-coated on a coverslip, and then calibratethe resolution of the system, which is an important precise in implementation ofCARS nanoscopy. The major contributions of the discussions are summarized asfollows:(1) We describe T-CARS process with full quantum theory and estimate theextreme power density levels of the excitation beams, which overcomes thedrawbacks of the explinations of CARS with semiclassic theory.(2) We provide a promising APIPD scheme for CARS microscopy that caneffectively suppress the extent of the focal spot to achieve resolution-enhanced images.For this purpose, an additional doughnut probe beam is utilized as the depletion light,and vibrational imaging of far-feld CARS microscopy with sub-diffraction-limitedspatial resolution can be effectively realized.(3) We report a theoretical analysis of the detection limit (DL) in a suppressedfocal volume, which necessitates a further research before constructing the CARSnanoscopy.(4) We apply CARS to demonstrate vibration imagings of polystyrene beadsspin-coated on a coverslip, and then calibrate the resolution of the system.A method based on centroid location algorithm is proposed to calculate the relative motions of the airy disk and the specimen. Only when the dimension of therelative motion is considerably below the theoretical resolution, we can achieve aresolution-enhanced image. Besides, we control the nanopositioning scanning stageand the detector with labview for auto-scanning, and a homemade data acquisitionsystem implemented in Matlab is used for image reconstruction. All of the workslay the foundation for suppressing the extent of the focal spot and achievingresolution-enhanced images.(5) We adopt femtosecond pump, stokes and probe pulses for CARS scheme tovertify exhaustion of the coherent phonons. We analyze the experiment results andraise the improvement methods for the following experiments. Meanwhile, wetheoretically analyze the process of spiral phase plate forming a doughnut beam. Weset up a supercontinuum generaction suit, and theoretically analyze the The physicalmechanism of supercontionuum.