OPTICAL POWER LIMITING AND STABILIZATION BASED ON A NOVEL POLYMER COMPOUND

Optical power limiting and stabilization based on the two-photon absor ption (TPA) mechanism is performed in a polymer solution excited by si milar to 810 nm and similar to 7-ns laser pulses. The solute is a nove l polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EHO -OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d(0) = 0.03 mol of repeat unit/liter as the nonlinear absorptive medium, t he dynamic transmission changes from T = 0.92 to 0.28 when the input i ntensity of the similar to 810-nm laser beam is increased from I-0 = 1 5 to 600 MW/cm(2). The measured nonlinear absorption coefficient beta is 14.5 cm/GW. Optical power stabilization is demonstrated at an avera ge input intensity level of I-0 approximate to 400 MW/cm(2) with a Del ta approximate to +/-25% peak-power fluctuation of the laser pulse. Af ter passing through the nonlinear medium, the output peak-power fluctu ation is reduced to Delta approximate to +/-8%. The spectral-width eff ect of the input laser beam on the nonlinear absorption of the EHO-OPP E solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are sigma(2) = 66, 80, and 101 x 10(-20) cm(4)/GW, respec tively. This means that EHO-OPPE is one of the best known nonlinear ab sorptive materials for power limiting purposes.