Polarization-rotation switch using picosecond pulses in GaAs.
Photorefractive and free-carrier nonlinearities in GaAs transfer energy from a strong picosecond pump, which is linearly polarized at an arbitrary angle to a weak s-polarized probe, into a p-polarized beam propagating in the probe direction. By placing the GaAs between a crossed pair of high-quality polarizers that are set to extinguish the probe in the absence of the pump, an efficient, high-contrast, high-speed optical switch is realized. By varying the pumpprobe ratio, delay, fluence, and polarization, we can maximize the intensity of the p-polarized component. This intensity with the pump present divided by that without the pump, the on-off ratio, is approximately 2 at fluences as low as 0.03 mJ/cm(2) and approaches 10,000 at fluences of 15 mJ/cm(2) and pump polarizations of 45 degrees .
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