chapter  4
20 Pages

SHG Microscopy and Its Comparison with THG, CARS, and Multiphoton Excited Fluorescence Imaging

Second-harmonic generation (SHG) is a nonlinear eect that was discovered in 1961 by Franken, Hill, and Weinreich [1] where frequency-doubled 347 nm light was generated when intense 694 nm light from a ruby laser was focused on a quartz sample. Subsequently, with the development of short-pulse lasers that produce much higher instantaneous light intensity and improved methods to grow uniaxial birefringent crystals with large nonlinear susceptibility, SHG has been used as an eective approach for new wavelength generation. is greatly extends scientic researchers’ capability as most primary laser sources are in the visible/near-infrared spectrum, whereas the optical absorption of most materials is at bluer wavelengths.