SHG interferometry

In this way, collective molecular switching occurs, as illustrated in Figure 9.33. It is clear that the directional senses of the p-polarized second-harmonic light in positive and negative slopes of the field are the same, as experimentally observed. On the other hand, it is also easy to understand that two peaks appear for the s-polarized SHG at positive and negative sides of the zero field and have the opposite phases, and that the outer (inner) peaks in positive and negative slopes have the same phase, as also observed experimentally. Thus, the simple collective model shown in Figure 9.33 satisfies all the experimental results of SHG intensity and SHG interferometry. 

In this chapter we explore several aspects of interferometric nonlinear microscopy. Our discussion is limited to methods that employ narrowband laser excitation i.e., interferences in the spectral domain are beyond the scope of this chapter. Phase-controlled spectral interferometry has been used extensively in broadband CARS microspectroscopy (Cui et al. 2006 Dudovich et al. 2002 Kee et al. 2006 Lim et al. 2005 Marks and Boppart 2004 Oron et al. 2003 Vacano et al. 2006), in addition to several applications in SHG (Tang et al. 2006) and two-photon excited fluorescence microscopy (Ando et al. 2002 Chuntonov et al. 2008 Dudovich et al. 2001 Tang et al. 2006). Here, we focus on interferences in the temporal and spatial domains for the purpose of generating new contrast mechanisms in the nonlinear imaging microscope. Special emphasis is given to the CARS technique, because it is sensitive to the phase response of the sample caused by the presence of spectroscopic resonances. 

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