TPEF

The measured intensities of TPEF as a function of the spectral bandwidth, for GDD-compensated and TL pulses, are shown in Figure 8.2. The experiments were performed with the same average power at the sample (2.3 mW) for all bandwidths, using a red fluorescence standard slide (Chroma Technologies). We found that in the case of TL pulses, obtained via MIIPS compensation, the magnitude of TPEF... 

FIGURE 8.2 Dependence of the TPEF signal on the laser spectral bandwidth for TL (filled circles) and SOD-compensated (open circles) pnlses of the laser pulse. The linear relation between TPEF and bandwidth is observed only for TL (i.e., MllPS-compensated, pulses). (FromXi et al. Opt. Comm. 281(7) 1841-1849, 2008. Used with permission.)... 

Two-photon excited fluorescence (TPEF) is one of the most useful ways to quantify TPA in optical materials competing with nonlinear absorption. While nonlinear transmission yields absolute quantities describing TPA, TPEF requires knowledge of the collection efficiency if absolute data must be acquired. Thus, the use of standards is the method of choice to determine 5 in case of TPEF. 

Figure 3.18. Optical setup for determination of <5 using TPEF. (From Ref. [85] with permission of the American Institute of Physics.)...

The setup in Figure 3.18 uses TPEF for absolute determination of 8. Another setup can be used to determine absolute <5 by in situ second-order autocorrelation for the absolute quantification of TPA [366], The approach is to access absolute TPA without knowledge of gc. A general scheme is depicted in Figure 3.19. 

Thus, two beams with equal intensities perfectly overlap in space but they are temporally shifted by the delays ts resulting in a fluorescence signal depending on ts. The original and the delayed beams are represented by P(t) and P(t + fs), respectively. As a result, the amount of TPEF recorded is about twice the amount generated by a single pulse of one of the half-beams. The TPA cross section is thus expressed by Eq. (43) ... 

TOL, toluene THF, tetrahydrofurane DMSO, dimethylsulfoxide CH3CN, acetonitrile CHC13, chloroform. TPEF, two-photon excited fluorescence WLC, white light continuum NLT, nonlinear transmission. cfs, femtosecond ps, picosencond ns, nanosecond. 

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