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Frontiers in Optics

Observation of superluminal of light propagation in doped Phthalocyanine with PMMA glass

Yundong Zhang, Qiuyun Ouyang, Hao Wang, Nan Wang, He Tian, Wei Qiu, Ping Yuan

Published Jan 1, 2007• 0 citations
Publisher

Abstract

We observed the superluminal of light propagation by population oscillation technique in doped Phthalocyanine with polypropyl methacrylate (PMMA) glass. The maximum time advancement was 10.43ms, corresponding group velocity was −0.19m/s.
DOI
10.1364/fio.2007.fwi4

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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.
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.
In this article we report on ultraslow or fast light propagation, exciting behavior that become achievable thanks to the Coherent Population Oscillations effect (CPO). We show that the group velocity, the speed at which light propagates, can be drastically modified and engineered using the CPO effect in a crystal doped with triply ionized erbium ions, namely: Er 3+ :Y 2 SiO 5 . The steep dispersion of the index of refraction caused by the CPO effect is at the origin of group velocities as low as v g = 3 m / s . By inverting the slope of the index dispersion, we can make, in the same crystal, light go faster than if it was propagating in vacuum. This particular regime is characterized by larger than c or negative group velocities. In the 3-mm-long Er 3+ :Y 2 SiO 5 crystal, we have achieved a delay of − 0.2 ms corresponding to a group velocity of v g = − 15 m / s .
Slow and superluminal group velocities can be observed in any material that has large normal or anomalous dispersion. While this fact has been known for more than a century, recent experiments have shown that the dispersion can be very large without dramatically deforming a pulse. As a result, the significance and nature of pulse velocity is being reevaluated. In this review, we discuss some of the current techniques used for generating ultra-slow, superluminal, and even stopped light. While ultra-slow and superluminal group velocities have been observed in complicated systems, from an applications point of view it is highly desirable to do have this done in a solid that can operate at room temperature. We describe how coherent population oscillations can produce ultra-slow and superluminal light under these conditions.
Nondegenerate two-wave coupling process and group velocity change in the paraxial part of an intensity-modulated and focused transverse electromagnetic beam (TEM00 beam in the article) was observed in the rhodamine 6G(R6G)-doped polymethyl methacrylate (PMMA) but not in the pure PMMA. The typical superluminal result was −5.1 m/s and the subluminal result was 9.19 m/s, respectively. Furthermore, the results provide a support to our former conclusion that nondegenerate two-wave couplinglike mechanism could be used to change the group velocity of the paraxial part of a focused TEM00 beam in materials with nondegenerate two-wave coupling process.