SHG efficiency

The earliest NLO studies involving metal pyridyl complexes were reported by Frazier et al. in 1986 who investigated the SHG properties of various group 6 metal pyridyl carbonyls.63 Although most of the complexes tested show little or no activity, (6) and (7) have respective SHG efficiencies of 0.2 and 1.0 times ADP using a 1,064 nm laser.63 Shortly after, Calabrese and Tam reported SHG from the Re1 complex (8).64 Subsequent studies by Eaton and Tam et al.65,66 describe the preparation of inclusion compounds of various metal complexes with thiourea or tris-ort/ o-thymotide. Unfortunately, none of the complexes [W(CO)5L] (L = pyridine, py, or a 4-substituted py) produce SHG-active materials.65,66... 

The advantages described above of using waveguiding structures can cancel out if the field overlap integral of the interacting modes is small. This arises since the SHG efficiency is proportional to it. 

We remind the reader that Eq. (12) is derived under conditions where the effects of pump depletion are neglected. In much the same way as it was described in section 2.2, we can expand the application of Eq. (12) for the range of higher pump intensities for which the depletion of the fundamental is weak but essential. The corrected value for the SHG efficiency,, which accounts for the effects of pump depletion is ... 

Figure 13. (a) Relative blue pulse peak powers from bulk appKTP and bulk KNb03 crystals, (b) Dependence of SHG efficiency on fundamental spectral bandwidth of femtosecond Cr LiSAF laser. 

In modeling the SHG performanee of the bulk nonlinear optical crystals, we have assumed the incident fundamental pulses are characterized by a hyperbolic secant temporal profile, and therefore r = rg (FWHM)/l.76. For the case of KNhOs, the maximum optical-to-optical SHG efficiency achieved was 30%. The corresponding value of L/L, under these conditions, with a GVM parameter, 1.2 ps/mm, is L/L = 30. The values of beam... 

Figure 15. Experimental values of SHG efficiency using the bulk KNb03 crystal tkta points), and the predictions of our model (gray curve) and another model (black curve) for L/L t = 30, as a function of the focusing strength, m = L/b. The theoretical curves are normahzed to their values for L/b = 10, which was the experimental optimal focusing strength. The maximum experimental point refers to a SHG efficiency of 30%.

When using the waveguide ppKTP crystal experimentally, the dependence of internal SHG efficiency on input power is characterized by a maximum efficiency of 37 %. A further increase in fundamental pulse energy then leads to a saturation and subsequent decrease in the efficiency of the SHG process (figure 18). This behavior was also observed in the waveguide appKTP crystal (figure 18), and has been reported elsewhere" ". As we have suggested previously, two-photon absorption (TPA) of the second-harmonic (SH) wave is the most likely explanation for this behavior. 

Figure 18. Saturation of SHG efficiency in the waveguide (ppKTP and appKTP) experiments (point data). Theoretical predictions incorporating the effects of two-photon absorption for the SH wave and group velocity mismatch are also shown for the ppKTP (dashed line) and appKTP waveguides (solid line).

Of the four nonlinear crystal types investigated in this paper (figure 20), bulk KNbOs was superior in terms of generated blue average power (11.8 mW) and generated beam quality. KNbOs is also less susceptible to the observed saturation and subsequent decrease in SHG efficiency observed in both waveguide crystals. 

Optical frequency up-conversion, or second harmonic generation (SHG), in nanostructured surfaces can be also considered as a kind of field enhance-menf [61]. In general, SHG efficiency is proportional to the square of nonlinear polarization ha (x [P (2second order susceptibility. For a nanostructured surface, the incident field is transformed to the local field given by Eq. 19, yielding ... 

Table I. Powder SHG efficiencies for R-CH=CH-C5H4NCH3+X salts. The left value is for 1064 nm input and the right value is for 1907 nm input (Urea = 1)...

Table II. Powder SHG efficiencies of (EMC5H5)Fe(C5H4)-CH=CH-(4)-C5H4N(CH3)+X- salts...

Further improvements in the magnitude of the nfi product which is proportional to (2) are possible -- current ADPM dyes have only 10% of the theoretical maximum value. Considerable effort will be required to design and synthesize these advanced dyes, but is justified on the basis of theoretical SHG efficiency gains of 10. ... 

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