Kishore Sridharan

Optical nonlinearity in lead sulfide microtowers

Lead sulfide (PbS) microtowers on silicon substrates, having the physical properties of bulk PbS, have been synthesized. Optical nonlinearity studies using the open aperture z-scan technique employing 5 ns and 100 fs laser pulses reveal effective two-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (βeff) are in the order of 10−11 m W−1, two orders of magnitude less than the values reported for quantum confined PbS nanocrystals. For femtosecond excitation βeff is of the order of 10−14 m W−1. These results obtained in bulk PbS experimentally confirm the importance of quantum confinement in the enhancement of optical nonlinearities in semiconductor materials.