Fundamental beam

The layout of the experimental set-up is shown in Figure 8-3. The laser source was a Ti sapphire laser system with chirped pulse amplification, which provided 140 fs pulses at 780 nm and 700 pJ energy at a repetition rate of 1 kHz. The excitation pulses at 390 nm were generated by the second harmonic of the fundamental beam in a 1-nun-thick LiB305 crystal. The pump beam was focused to a spot size of 80 pm and the excitation energy density was between 0.3 and 12 ntJ/crn2 per pulse. Pump-... 

A feature of interest is the possibility of obtaining the condition of total internal reflection (TIR). Under this condition, the fundamental beam impinges on the interface from the liquid with the highest index of refraction yielding a SH intensity enhancement of more than a hundred times. Two TIR angles exist, given by the following relationships ... 

FIG. 5 Time-resolved SHG intensity from the doubly charged eosin B at the air-water interface after randomization of the orientation distribution, (a) Square root of the SH signal recorded for the s-polarized SHG output intensity and the fundamental beam 45°-polarized. (b) Square root of the SH signal recorded for the p-polarized SHG output intensity and the fundamental beam s-polarized. (From Ref 96, copyright Elsevier Science BV.)... 

Figure 9.8 Second-harmonic generation from thin film (or surface). Fundamental beam at frequency > i p or. v polarized) is incident on film at angle 0. The p- and. s-polarized second-harmonic fields (frequency 2 co) are generated in reflection and transmission. 

The nonlinearity of the sample was analyzed using the experimental procedure described in Section 3.3 The polarization of the fundamental beam of a YAG laser was continuously varied by means of a quarter waveplate, and the intensity of the second-harmonic signal was measured as a function of the rotation angle of the quarter waveplate. The obtained polarization pattern were then fitted to Eq. (42), which yields the relative values of the expansion coefficients /, g, and h. The experimental results for the transmitted, glass-side-incidence, s-polarizcd signal are shown in Figure 9.20. 

The natural way to increase the efficiency of such a frequency conversion process is to use a focused fundamental beam (or, alternatively, a waveguide structure). An established theory of SHG using focused cw beams " predicts, for negligible birefringence waUc-off, an optimal focusing condition which is expressed by the ratio L/b 2.83, where b is the confocal parameter (b = k wQ, where Wqi and ky are the focal spot radius and the wave vector of the fundamental wave respectively). However, this theory applies only to the long-pulse or cw case, where GVM is negligible... 

Figure 6. SHG intensity from a glass slide having self-assembled CpCh monolayers on both sides as a function of fundamental beam incident angle. The interference pattern is due to the phase difference between the SHG waves generated at either side of the substrate during propagation of the fundamental wave. The solid envelope is a theoretical curve generated for Xzzz/ zyy " 3-...

The fringes are created by the rotation of the sample along an axis which is parallel to the fundamental beam polarization. Since many of the samples have strong absorptions at 3co, care was taken to include accurate measurements of both the polymer refractive index and absorption coefficient at 3m in the analysis. Failure to... 

In this case the output field is a radiation wave which leaves the vicinity of the waveguide, i.e. the output field is not guided. For co-propagating fundamental beams it has been shown that the Cerenkov SHG signal grows initially quadrat-ically and then later linearly with distance. A comparison of the growth of the SHG power for different phase-matching cases is shown in Fig. 7. 

This counter-propagation Cerenkov experiment is easy to perform because one has only to launch the fundamental beams at both ends of the guiding structure [53]. This technique is very stable and puts very few constraints on the material... 

Fig. 11. (a) s-Polarization analyzed SHG spectrum of adsorbed TPPS at the heptane-water interface, lcp left-circularly polarized fundamental beam, rep right-circularly polarized fundamental beam, (b) SHG/CD spectrum of adsorbed TPPS at the heptane-water interface. Aqueous phase was containing 5.35 x 10 M TPPS, 3.36 x 10"7M CTAB, 0.001 M HC1 (pH 3.0), and 0.009 M NaCl. 

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