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Conference on Lasers and Electro-Optics

Low-power saturation of bound excitons and observation of optical bistability

M. Dagenais, Herbert G. Winful

Published Jan 1, 1983• 1 citation
Publisher

Abstract

Very large nonlinearities are observed in the vicinity of a bound exciton resonance in cadmium sulfide. Power levels of the order of 8 μW are sufficient for saturating the bound exciton resonance in a tight focusing geometry. In a more loosely focused geometry, power levels of the order of 250 μW are sufficient for saturating the bound exciton resonance and for observing optical bistability. Transverse effects are found to play a very important role. For all our measurements, no thermal contributions to the nonlinearity were observed. Since thermal effects are not playing a role and since the studied bound excitons decay radiatively in 500 psec, we infer subnanosecond switchoff and cycling times.

DOI
10.1364/cleo.1983.wh4

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Low Power Optical Bistability Near Bound Excitons in Cadmium Sulfide

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Low Power Optical Bistability near Bound Excitons in Cadmium Sulfide

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Springer eBooks•Jan 1, 1984•3 citations
Very large nonlinearities are observed in the vicinity of a bound exciton resonance in cadmium sulfide. Power levels of the order of 8 μW are sufficient for saturating the bound exciton resonance in a tight focusing geometry. In a more loosely focused geometry, power levels of the order of 250 μW are sufficient for saturating the bound exciton resonance and for observing optical bistability. Transverse effects are found to play a very important role. For all our measurements, no thermal contributions to the nonlinearity were observed. Since thermal effects are not playing a role and since the studied bound excitons decay radiatively in 500 psec, we infer subnanosecond switchoff and cycling times.
The I2 bound exciton in cadmium sulfide has a giant oscillator strength of 6. It decays mostly radiatively in 500 psec. Such a large oscillator strength leads to a very large transition dipole moment and to very large nonlinear effects off-resonance. At 2K, this sytem saturates like an inhomogeneously broadened system for intensities up to 30 times the saturation intensity. The transition linewidth is 7.5 GHz. In a tight focusing geometry, only 3.6 μW is required to see the onset of saturation. This corresponds to a measured saturation intensity of about 60 W/cm2. The linear absorption coefficient right at the resonance peak was measured to be 3.2 x 103 cm-1. At higher temperatures, the transition linewidth broadens and the line becomes more and more homogeneously broadened because of phonon interaction. At intensities above 50 times the saturation intensity, the absorption coefficient stops decreasing and then starts increasing. At these high intensities, thermal effects appear to play a significant role in shifting the free and bound exciton resonances toward lower energies. At intensities less than 20 times the saturation intensity, thermal effects are believed to be insignificant in our saturation measurements.