Slow And Fast Light In Media With Saturated And Reverse Saturated Absorption

In recent years, slow (v_gg is the group velocity of light in media, c is the speed of light in vacuum) and fast light (v_g>c or v_g<0), as new physical phenomena, have attracted great interests in researchers in optics and material for their potential application in telecommunication and optical signal processing. Undoubtedly, as a new issue, researches in slow and fast light are still in progress and some basic problems need to be solved, to some extent. Based on the reality in this field, the author set up the theoretical model of the reaction between light and material and put forward a new way to select material for slow and fast light. Through detailed experimental observation, we find that our experimental results confirme the theoretical prospect. Our results on slow and fast light in saturation absorption and reverse saturation absorption materials will be helpful on the understanding of the related phenomenon and will be of significance on the future application of slow and fast light.Firstly, the author introduced the different definitions of the light speed and reviews the recent progress in the researches on slow and fast light. Also, the author introduced the techniques in the researches on slow and fast light including electromagnetically induced transparency and coherent population oscillations. Based on detailed analysis on above techniques, the author presented the theoretical model of density matrix and gave the theoretical calculations by this method. The calculated results had good agreement with the published results.Secondly, based on the analysis on the model of density model, media with saturated absorption will demonstrate slow light property and those with reverse saturated absorption will have fast light property. Take this method, we selected C₆₀, which has strong reverse saturated absorption optical property in the visible region, as superluminal candidate and experimentally observed fast light in C₆₀ solution with negative group velocity, firstly. The experimental results confirmed our theoretical prospect. Otherwise, in order to overcome the drawback of liquid sample of C₆₀ solution, we fabricated the solid of C₆₀ PMMA and observed the fast light phenomenon in it. This will be helpful for the possible application of fast light in C₆₀ in the future.Thirdly, we extended our work to other material which has similar RSA property with C₆₀ molecule. And we observed fast light in phthalocyaine gallium PMMA firstly. This experimental result confirmed the validity of our method in selecting materials for slow and fast light.Fourthly, in present, the understanding on slow and fast light was based on dispersion. In our work, taking use of the K-K relation, we gave the visual explanation on slow and fast light founded on absorption firstly. In experiment, the author put forward a way to observe the signal evolution of slow and fast light, by virtue of signal with non-analytical points. By this way, the author observed the slow light signal evolution in material with saturation absorption and fast light signal evolution in material with reverse saturation absorption successfully. We got that the generation of slow and fast light could be attributed to the asymmetrical absorption on the periodical signal. The author also discussed the information speed of slow and fast light. We concluded that the information speed would not exceed c, whenever slow or fast light was observed. Our conclusion was in agreement with the causality of the special relativity.Lastly, by virtue of nonanalytical pulse, we traced the signal evolution of slow and fast light in erbium doped optical fiber. Experimental results confirmed our point that asymmetrical absorption and amplification on the periodical signal gave rise to the slow or fast light in erbium doped optical fiber.Our researches enrich the theoretical and experimental investigations on slow and fast light. Our experimental results demonstrated, directly, the mechanism of the generation of slow and fast light in SA and RSA media, respectively. These results will be of significance on the investigation in related fields in the future and will back up the possible application of slow and fast light.