<title>Self-focusing in bioengineered polymers</title>

Self-focusing of ruby laser beams is observed in solution for a series of bioengineered polymers. The values obtained for third order nonlinear optical susceptibility (Chi) <SUP>(3</SUP>) are compared with observed values by degenerate four wave mixing. It is demonstrated that self- focusing is a sensitive technique for measuring (Chi) <SUP>(3</SUP>).