Coherent Raman Scattering:Applications in Imaging and Sensing.

[摘要] In this thesis, I discuss the theory, implementation and applications of coherentRaman scattering to imaging and sensing. A time domain interferometric methodhas been developed to collect high resolution shot-noise-limited Raman spectra overthe Raman fingerprint regime and completely remove the electronic background signalin coherent Raman scattering. Compared with other existing coherent Ramanmicroscopy methods, this time domain approach is proved to be simpler and morerobust in rejecting background signal. We apply this method to image polymersand biological samples and demonstrate that the same setup can be used to collecttwo photon fluorescence and self phase modulation signals. A signal to noise ratioanalysis is performed to show that this time domain method has a comparablesignal to noise ratio to spectral domain methods, which we confirm experimentally.The coherent Raman method is also compared with spontaneous Raman scattering.The conditions under which coherent methods provide signal enhancement arediscussed and experiments are performed to compare coherent Raman scatteringwith spontaneous Raman scattering under typical biological imaging conditions. Acritical power, above which coherent Raman scattering is more sensitive than spontaneousRaman scattering, is experimentally determined to be ~1mW in samples ofhigh molecule concentration with a 75MHz laser system. This finding is contrary toclaims that coherent methods provide many orders of magnitude enhancement undercomparable conditions. In addition to the far field applications, I also discuss the combination of our time domain coherent Raman method with near field enhancementto explore the possibility of sensing and near field imaging. We report the firstdirect time-resolved coherent Raman measurement performed on a nanostructuredsubstrate for molecule sensing. The preliminary results demonstrate that sub 20fs pulses can be used to obtain coherent Raman spectra from a small number ofmolecules bound to a specially engineered metal structure and pave the way for abroad range of near field nonlinear experiments which require such short pulses.

[发布机构] University of Michigan

[效力级别] Nonlinear Microscopy

[关键词] Coherent Raman Scattering;Nonlinear Microscopy;Physics;Science;Physics