Second harmonic wavelength

A normalized conversion efficiency of 7% W xcm 2 was achieved in a first experiment. Although very high propagation loss of about 100 dB/cm at the 800 nm second harmonic wavelength resulted from the repoling, these figure of merit values were further increased to 14% W xcm 2 for a 1 mm device [78]. It is probable that the interface between the two oppositely poled regions is the source of the loss. Another theoretical route that requires special materials... 

As was discussed above the necessary condition for Cerenkov-type phase-matched frequency-doubling is that the effective refractive index of the fundamental mode is smaller than the refractive index of the substrate at 2flX This condition can be fulfilled for DCANP deposited on pyrex. Table 1 lists the refractive indices at the fundamental and the second-harmonic wavelengths, the thicknesses t of the films used in our experiments and the calculated and measured Cerenkov angles. As can be seen from Table 1 the Cerenkov angles 0 co/c and Q meas are in agreement within the experimental errors. 

I. Shogi, H. Nakamura, K. Obdaira, T. Kondo, R. Ito Absolute measurement of second order nonlinear-optical cefficient of beta-BaB204 for visible and ultraviolet second harmonic wavelengths. J. Opt. Soc. Am. B 16, 620 (1999)... 

For frequency doubling, some additional demands should be fulfilled, viz. phase matching and a very low absorption at both the fundamental and second harmonic wavelength. Several proposals have been made to obtain phase matching In polymer waveguides and work along these lines is in progress. 

For operation at 1550 nm, the efficiency is still severely reduced by absorption at the second-harmonic wavelength, which can be seen by comparing the theoretical performance including absorption (curve) and excluding absorption (open circle). Since DANS is a bleachable chromophore, waveguide damage is to be expected at higher SHG intensities, which was in fact observed [26]. 

If there is no absoqMion at fundamental ( ) and second harmonic wavelengths ifre fd-lowing NLO ooefli nls are obtained according to Kkininan s symmetry ... 

Second-order nonlinear coefficients of ZnO have been deduced also by including the absorption at the second harmonic wavelengths for ZnO thin films, confirming the enhancement of the second-order nonlinearity due to the microcrystalline structure [195]. They were measured to be significantly larger than those in bulk ZnO. 33, dji, and dis were reported to be —83.7, 14.7, and 15.2pmV , respectively, at 1064nm for ZnO thin films deposited on sapphire by laser MBE [195]. 

The first examples of nonoxidized Cu NPs produced by LA in soluhon were provided by Yeh and collaborators, who converted an isopropanol suspension of CuO powder into Cu NPs by using a Nd YAG laser [both fundamental (1064nm) and second harmonic wavelengths were investigated] [284]. A few years later the same authors investigated the effect of thiols on the system [285], while Tsuji et al. studied the influence of laser wavelength on the efficiency of ablation of metallic copper targets immersed in an aqueous solution [286]. 

The major requirements for the NLO moiety of SHG are a high first-order hyperpolarizability and complete transparency at both the fundamental and the second-harmonic wavelengths. Nevertheless, most of the highly NLO-active chromophores are colored and are not suitable for SHG in the visible regions. The methylsulfonyl acceptor combined with relatively weak donor alkoxy in some stilbene compounds has relatively good balance between transparency and NLO effects. The copolymers of methyl methacry-... 

A general method to realize phase-matching, is to use the natural birefringence in certain anisotropic crystals to compensate for the refractive index dispersions between the fundamental and second-harmonic wavelengths and realize ni = nL [167-169]. There are two types of collinear... 

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