We present measurements of induced absorption and its dynamics in C60-doped solid xerogel matrices. The measurements are performed in a pump-test geometry using picosecond pulses generated from a frequency doubled mode locked Nd:YAG laser at 532 nm. We observe an induced absorption leading to optical limiting. We find outstanding optical limiting qualities for single shot excitation but some degradation above a certain threshold intensity for repetitive pulses. Below this degradation threshold, the material is stable and its limiting dynamics is studied. A decrease of the initial laser-induced absorption with a time constant of 150 ps is observed, down to a very long-lived constant level. We attribute this dynamics of induced absorption to a transition from excited singlet to triplet electronic states in the C60 molecule.

We calculate the excitonic transition energy in T-shaped quantum well wires. The complexity of the valence band is taken into account. This leads to a description of the exciton where the hole is bound mainly to the electron when the wire valence band confinement potential is too weak. This allows one a comparison with experimental results obtained in Ga1 − xAlxAs T-shaped quantum well wires with widths of 70 and 50 Å and x = 0.3 and 0.35. PACS numbers: 73.20.Dx, 78.55.Cr, 78.55.Et

We give a general framework for describing electronic states in isolated quantum wires. It provides a description of both the conduction band and the valence band, taking full account of the complexity of the rs valence band. This is applied to T-shaped wires and V-shaped wires. To make a useful comparison with experimental results we calculate the exciton Rydberg. We show that in the case of the T-shaped wires hole confinement is due to the interaction with the confined electron and not due to the confining potential: the red shift of the wire exciton line with respect to that of the quantum well is mainly due to the decrease of the electron confinement energy and only partially to the increase of the exciton Rydberg. The experimental results are reproduced with no adjustable parameters.

We give a general framework for describing electronic states in isolated quantum wires. It provides a description of both the conduction band and the valence band, taking full account of the complexity of the r8 valence band. This is applied to T-shaped wires and V-shaped wires. To make a useful comparison with experimental results we calculate the exciton Rydberg. We show that in the case of the T-shaped wires hole confinement is due to the interaction with the confined electron and not due to the confining potential: the red shift of the wire exciton line with respect to that of the quantum well is mainly due to the decrease of the electron confinement energy and only partially to the increase of the exciton Rydberg. The experimental results are reproduced with no adjustable parameters.