Large Field Of View Chemical Tomography Based On Coherent Raman Scattering

Large field-of-view(FOV)optical imaging has played an indispensable role in clinical medicine and life science,such as optical coherence tomography,photoacoustic imaging and light sheet microscopy.These widely used large FOV tomography methods generally require fluorescent labeling,or are only specific to blood vessels,so it is difficult to obtain chemical information while recognizing the structural characteristics of the samples.Although the coherent Raman scattering imaging technology based on chemical bond can achieve chemical specific imaging,the FOV is small.It is also difficult to achieve high-resolution chemical tomography of biomolecules in a large-depth scale.Therefore,large FOV optical tomography imaging specific to biomolecules is of great research importance.This thesis developed large FOV chemical tomography imaging system based on counter-propagating femtosecond pulse,which realizes the label-free imaging of protein,lipid and water in biological tissues by stimulated Raman scattering(SRS).The imaging depth was further explored,NIR-ⅡandⅢsource for tissue optical windowsⅡand IV was developed,and coherent anti-Stokes Raman scattering(CARS)imaging with a large FOV was realized.The main contents of this thesis are listed as follows:(1)Near infrared SRS tomography system based on the counter-propagating femtosecond pulse was designed and built.The mechanism of chemical tomography using phase-locked pulses was analyzed,and a time delay system was used to scan the axial imaging plane.Combined with the large FOV laser scanning method,three-dimensional tomographic chemical imaging of tissues,such as whole skull,scalp,and ear was realized.Finally,a high-resolution tomography system with a FOV of more than 1×1 cm~2,imaging depth of more than 1 mm,lateral resolution～16μm,and axial resolution～24.5μm was built.(2)As for improving imaging depth,this work developed the scheme of using laser source of tissue opticalⅡand IV transmission windows to realize NIR-ⅡandⅢcoherent Raman scattering tomography.Due to the lack of high-repetition phase-locked dual femtosecond NIR-ⅡandⅢlaser source,1 300 nm Raman soliton of rather high power and polarization extinction was generated as the signal laser via the photonic crystal fiber pumped by femtosecond solid laser source.The optical parametric amplification of the signal laser was realized by the PPLN crystal,and a 2 080 nm idler laser was generated.The final power is increased to 200 m W for signal laser at 1 300 nm and 90 m W for idler laser at 2 080 nm.(3)NIR-ⅡandⅢCARS chemical tomography system was built.Large FOV and large axial scale detection device was developed,thus label-free CARS imaging of thick tissue such as brain and muscle sample was realized.The relationship between imaging depth and laser absorption of bone,mouse brain tissue and water was analyzed.In summary,in view of the requirements for large FOV optical imaging of tissue,this thesis built a coherent Raman scattering chemical tomography system,which simultaneously meets the demand of large FOV and high axial resolution.In addition,it explored the limitation of imaging depth by extending the wavelength to optical tissue windows,and has guiding significance for the development of large-volume optical tomography.