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Conference on Lasers and Electro-Optics

Polarization dynamics induced by the "virtual excitation" of spin-polarized carriers: applications to all-optical polarization switching

Eric J. Gansen, Arthur L. Smirl

Published Jun 25, 2003• 0 citations
Publisher

Abstract

Summary from only given. Recently we have demonstrated an optically-addressed coherent polarization switch that is based on the near-resonant excitation of a spin-polarized population of virtual excitons in MQWs. By taking advantage of the nonlinearities associated with a virtual carrier population, this near resonant device exhibits a pulse-width-limited response; by operating near resonance it is capable of producing relatively large contrast ratios in thin samples; and finally, by generating a spin-polarized carrier population, the device produces a rotation of the signal polarization in unstrained MQWs. Here, we experimentally analyze the switching mechanisms by systematically performing spectrally and temporally resolved differential transmission measurements and by fully determining the polarization state of the transmitted signal as a function of time delay.

DOI
10.1109/cleo.2002.1034446

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Summary from only given. Recently we have demonstrated an optically-addressed coherent polarization switch that is based on the near-resonant excitation of a spin-polarized population of virtual excitons in MQWs. By taking advantage of the nonlinearities associated with a virtual carrier population, this near resonant device exhibits a pulse-width-limited response; by operating near resonance it is capable of producing relatively large contrast ratios in thin samples; and finally, by generating a spin-polarized carrier population, the device produces a rotation of the signal polarization in unstrained MQWs. Here, we experimentally analyze the switching mechanisms by systematically performing spectrally and temporally resolved differential transmission measurements and by fully determining the polarization state of the transmitted signal as a function of time delay.
Summary form only given. We describe a novel optically-addressed coherent polarization switch that is based on the non-resonant excitation of spin-polarized "virtual excitons" in unstrained MQWs. By operating near (but below) resonance, we achieve nonlinearities that approach the magnitudes of those that can be obtained with resonant excitation, yet we are able to avoid the restrictions that accompany carrier generation, and we take advantage of speeds that are characteristic of non-resonant excitation. Consequently, our device exhibits a pulse-width-limited response that is determined solely by the length of the control and signal pulses and produces large contrast ratios in thin MQW samples.
By using a circularly polarized pulse that is tuned well below resonance, we create a virtual population of spin-polarized coherent excitons in a GaAs/AlGaAs multiple quantum well, and we study its effects on the polarization state of a weak signal pulse using a combination of time-resolved and spectrally resolved ellipsometric techniques. From these data the polarization state contributions to an all-optical polarization switch, which exhibits a ~415 fs switching time and large contrast ratios, are identified and the performance of the switch is demonstrated.
This chapter discusses some experiments on coherent control of carrier densities, angular momenta, electron spin and exciton polarisations. The use of direct gap semiconductors as the active medium in all-optical switching devices is favoured by their large optical nonlinearities. The presence of spin polarised electrons in the sample can also be seen in the longer timescale dynamics after coherent carrier control. Selection of angular momentum is achieved by using shorter optical pulses which have a broad enough spectral content to excite both the heavy and light hole exciton states. Selected coherent pulse shaping techniques are introduced and used to demonstrate novel phenomena produced by coherent control in semiconductor heterostructures. New features in the interaction of light with semiconductor heterostructures are resolved, highlighting nonlinear mechanisms that can be of future use, as well as significantly modifying the picture of how light interacts with such samples.