Second harmonic generation coefficient measurements

Calculations which ascribe nonlinear optical polarizabilities in LilOa to the individual I-O bonds and relate experimentally measured second harmonic generation coefficients x 311 and X313 to theoretical results for the structure of LilOs, have been performed by Jeggo ii). 

Nonlinear optical properties. The optical nonlinearity was characterized by two experiments second harmonic generation (SHG) and electro-optic measurements. All of the results are listed in Table n. The second harmonic generation (SHG) for the poled polyimides was conducted to determine the second harmonic generation coefficients (das). PI 1 possessed the highest value of SHG... 

CB04. The spontaneous polarisation was measured by the pulse pyroelectric technique (Ps = 46 nC/cm ). The piezoelectric coefficient evaluated for CB04 was dsi = 1.6 pC/N. The estimation of the efficiency of the second harmonic generation for compound CB04 gives the value three times more than for quartz. 

Both theoretical analysis and dipole moment measurements indicated that sulfonyl-substituted compounds may have ft coefficients similar in magnitude to their nitro analogues. Therefore, we have measured p for several sulfonyl- and nitro-substituted compounds using electric-field-induced second-harmonic generation method (EFISH) (11,25). In this experiment, one measures an effective third-order nonlinearity rEFISH for a solution containing the compound of interest, given by... 

The nonlinear optical properties of thin films of the polymers were investigated through measurement of second-harmonic generation, and exhibit second-harmonic coefficients, d33, in the range 4.1-34 pm/V. 

Before we close this section, let us emphasize the importance of the degeneracy factor D in Eq. (28). This factor takes different values depending on the nature of the nonlinear optical process. For instance, in the case of second harmonic generation its value is unity, while for an electro-optic process it takes the value 2. Therefore, great care must be taken in reconciling experimental values of nonlinear coefficients measured using different experiments. 

A quite direct method for measuring x is based on second harmonic generation, SHG. Figure 3.3 depicts a typical set-up used to determine the SHG coefficients and d, defined as d=x l2, by way of SHG measurements. 

The refractive indices of M(CeH5)4 crystals (M = Si to Pb) are in the 1.58 0.05 range. The crystals are transparent from 325 to 1200 nm and are Class B second harmonic generators. Measurements of linear electro-optic effects show the rg3 coefficients to be in the range (17 + 1) X 10 m/V with half-wave retardation voltages of 5 kV [24]. 

Here ai is the frequency of the first strongly absorbing electronic transition in the molecule, and la and at are the fundamental wavelengths in second harmonic generation and for electrooptic coefficient measurements, respectively. The electrooptic effect (Pockels effect) is related to the corresponding second-order NLO susceptibility and by knowing the SHG coefficients, one can also estimate the electrooptic coefficients. 

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