ABSTRACT
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5.1.1 Pros and Cons of Femtosecond and Picosecond Laser Excitation Coupling of nonlinear optical (NLO) signal generation and scanning microscope has generated a panel of imaging tools for biology and materials research. ese tools include the one-beam modality such as two-photon excited –uorescence (TPEF), second harmonic generation (SHG), and third harmonic generation (THG) microscopy. e two-beam modality includes coherent anti-Stokes Raman scattering (CARS), four-wave mixing (FWM), stimulated Raman scattering (SRS), photothermal, and pump-probe microscopy (for a review, see Yue et al. [2011]). Due to nonlinear nature of interaction high peak power laser sources are required to generate strong signals. Although femtosecond (fs) laser sources provide highest peak power, the picosecond (ps) pulse excitation provides high spectral resolution for the Raman-based NLO modalities such as CARS and SRS. e advantages and disadvantages of both femtosecond and picosecond excitations are summarized in Table 5.1.
