Phase matching of backward second harmonic generation assisted by lattice structure in collagen tissues.
Phase matching of backward second harmonic generation (SHG) in a periodic structure of collagen fibrils is investigated through theoretical modeling, simulation, and experiments. The lattice structure of collagen fibrils is considered to provide a virtual momentum for assisting the phase matching of backward SHG. Phase matching over a relatively wide excitation wavelength range is achieved by tilting the angle of the fundamental excitation and SHG wave vectors. The SHG intensity in the periodic structure is simulated to quantify the phase matching effect. The effect of the fundamental excitation and the SHG emission angles on the peak excitation wavelength of the SHG excitation spectrum is further validated in experiments, where the excitation and emission angles are controlled by spatial filtering. It is found that an optimized excitation wavelength exists for a certain collagen fibril structure, which shifts toward a shorter wavelength when the excitation and emission angles are increased. Our results show that the lattice structure of collagen fibrils can assist the phase matching, providing a mechanism for generating backward SHG in multiphoton microscopy.
University of British Columbia, Department of Electrical and Computer Engineering, 2332 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Mengzhe
M
Shen
British Columbia Cancer Agency Research Centre, Integrative Oncology Department, 675 West 10th Avenue, Vancouver, British Columbia V5Z 1L3, CanadacUniversity of British Columbia and Vancouver Coastal Health Research Institute, Department of Dermatology an.
Haishan
H
Zeng
University of British Columbia, Department of Electrical and Computer Engineering, 2332 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Shuo
S
Tang
D003198:Computer Simulation; D024022:Fibrillar Collagens / Q000378:metabolism* / Q000648:ultrastructure*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D008954:Models, Biological; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D024022:Fibrillar Collagens