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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Backward propagation of light pulse in phthalocyanin gallium PMMA at room temperature

Hao Wang, Chunguang Zhang

Published Oct 8, 2010• 0 citations
Publisher

Abstract

Light speed control had been an interesting issue in recent years. In this work, the authors experimentally observed the backward propagation of light pulse in Phthalocyanin Gallium polymethyl methacrylate (PMMA) at room temperature, firstly. Taking use of the modulation technique, we got the time advancement of 260 μs when the sample length was 2 mm long and the modulation frequency was 50 Hz, the corresponding group velocity was -7.69m/s. The phenomenon of backward propagation was a direct result of negative group velocity. And the energy flow still traveled in the forward direction in the sample although the light propagated with a negative group velocity.

DOI
10.1117/12.870713

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Light speed control had been an interesting issue in recent years. In this work, the authors experimentally observed the backward propagation of light pulse in Phthalocyanin Gallium polymethyl methacrylate (PMMA) at room temperature, firstly. Taking use of the modulation technique, we got the time advancement of 260 μs when the sample length was 2 mm long and the modulation frequency was 50 Hz, the corresponding group velocity was -7.69m/s. The phenomenon of backward propagation was a direct result of negative group velocity. And the energy flow still traveled in the forward direction in the sample although the light propagated with a negative group velocity.
We investigated the light propagation in an organic glass with phthalocyanine gallium (GaPc) dispersed in polymethyl methacrylate (PMMA) fabricated by injection molding. The GaPc/PMMA organic glass is a reverse saturation absorption medium. We observed the superluminal propagation in this organic glass by using the technique of coherent population oscillations at room temperature. The largest time advancement is 2.21 ms and the corresponding group velocity is −0.90 m/s at the wavelength of 532 nm and with the input power of 89 mW. The density matrix theory with four-level model was used to analyze the experimental data. The theoretical simulations showed that the time advancement not only depends on the modulation frequency but also on the lifetime of the first triplet-state of the GaPc. We compared the time advancements between the GaPc/PMMA organic glass and the C60/toluene solution. Although the value of the former is smaller, it is more suitable for practical applications such as optical information processing than the latter.
We have observed slow light propagation with a group velocity as slow as 27.52±0.05m/s in a ruby crystal at room temperature. The Gaussian-like pulse signal, which was gained by modulating beam at 514.5nm, was injected into a ruby crystal. The spectral hole effect, attributed to high laser power density, leads to the induced refractive index steep rising. According as this rising, the group velocity of pulse propagation in the ruby becomes very slowly. The experiment result shows that the velocity of pulse propagation depends on the modulation frequency, laser power, the position of crystal and the profile of signal waveform. At the same condition the Gaussian-like pulse obtains much slower velocity than sinusoidal signal.
In this work, we experimentally demonstrate the capacity of the photorefractive (PR) crystal to control the group velocity of light pulses, specifically at the telecommunication wavelength, by using the so-called beam fanning at room temperature. Significantly, we show for the first time that this method can effectively decelerate a modulated signal propagating through this material at 1310 nm. Furthermore, we illustrate that the performance of this slow light system can be adjusted by changing the intensity, duration, and angle of polarization of the input pulse. The results obtained through this technique can potentially improve the performance of specific components in telecommunication networks.