Imaging nonlinear

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. 

Ultrafast spectroscopic approaches are increasingly being applied to imaging in terms of both nonlinear imaging and dynamics. This is driven partially by the improvement in and ease of use of ultrafast laser systems and detectors. It is not possible to review all of the methods currently under development, but several examples are given below. 

M. Nagorni, S.W. Hell, Coherent use of opposing lenses for axial resolution increase in fluorescence microscopy. II. Power and limitation of nonlinear image restoration. J. Opt. Soc. Am. A 18(1), 49-54 (2001)... 

The opto-electric conversion characteristic can be designed as linear or nonlinear. A linear CMOS imager experiences numerous drawbacks that are typically known with CCDs, especially the limited dynamic range. Several developments of nonlinear imagers with an extended dynamic range have been presented. 

Logic-based Nonlinear Image Processing, Stephen Marshall, Vol. TT72... 

Section 12.6, where other nonlinear device/concepts that are effective for the short time scale will be introduced. It is interesting to note that if one combines the nematic films with the nonlinear (image transmitting) fiber array for nanosecond/picosecond limiting apphcation (cf. Sec. 12.6), it is possible to fashion optical sensor protection devices capable of covering an extremely wide temporal range (from ps laser pulses to cw hght sources). 

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