THG in Polymer Solutions

Different techniques used in THG experiments on liquids have been discussed by Kajzar (1989 ). The most convenient is that proposed by Kajzar and Messier (1987)(cf. Fig. 14) and consisting on use of a wedge shaped liquid compartment with thick input and output windows. The liquid cell is translated perpendicularly to the beam propagation direction. Harmonic fields generated in input and output windows are bound waves whose intensities are independent on translation x. Only that generated in liquid compartment, where laser beam is considered as plane wave, varies with x. The harmonic fields generated in air before and 

Due to the phase mismatch dtp in liquid compartment the resultant harmonic intensity varies periodically as a function of x (cf. Fig. 15). From the observed periodicity one can determine easily the coherence length and from the amplitude of harmonic intensity one can get of liquid by comparison with a known standard (e.g. a silica slab or a known solvent). 

From the concentration variation of the amplitude of normcdized harmonic Intensity for a polymer solution with respect to that of the solvent one can get the modulus and the phase of solute cubic susceptibility if that of the solvent is known using the following formulas (cf. Kajzar (I989)) 

The factors S and P take account of absorption at fundamental and harmonic frequency, respectively and are given by 

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