Experimental Observation On Two-wave Mixing And Dissipative Solitons In Organic Photorefractive Material

Since laser came forth from 1960's, a series of optical phenomena arised from nonlinear optical effects have appeared. Optical soliton is one of the most important phenomena. When sel-focusing effect induced by the nonlinear effect of the media balances the diffraction, the beam becomes optical soliton. One of the most important solitons is photorefractive soliton. This kind of soliton arises from photorefractive effect in the material. When refractive index grating forms, the focusing effect arises. The focusing effect can banlance the diffractive effect. Because photorefractive effect can be produced even when the optical power is very small, photorefractive soliton can be used in a wide range of applications.One kind of the photorefractive soliton is holographic soliton. Normally, we call the spatial solitons arising from the holographic focusing mechanism as holographic solitons. According to whether the asymmetric energy exchange between two beams takes place or not during the forming of the holographic solitons, the holographic solitons can be divided into hamitonian holographic solitons (HHS) and dissipative holographic solitons (DHS). For DHS model, one beam can act as pump beam to supply energy for the other beam, which behaves as the signal beam. Through the photorefractive two-beam coupling process, a strong pump beam can give energy transfer to a weak signal beam and form asymmetric energy transfer. The gain of the signal beam can offset the absorption loss of the system. Holographic focusing effect can offset the diffractive effect. At this time, dissipative holographic soliton is produced.At present most of the materials on photorefractive solitons are inorganic electro-optical crystals. The experimental reports on photorefractive solitons in organic materials are few. The crystals are expensive and hard to prepare. But organic photorefractive material have good nonlinear effect and electro-optical effect, and easy to prepare. So people want to use organic photorefractive material to substitute crystals.We synthesized a second-nonlinear carbazole derivative 3-acyl-9-vinyl carbazole. Doping a few mass of sensitizer 2,4,7-trinitro-9-fluorenone (TNF) in this molecule. The photorefractive material was synthesized by only two components and the process was easy to take, which offers a good foundation for its application. We do experiment on the carbazole material to find if it has photorefractive effect. First, we using He-Ne laser to constructe a two-beam coupling(2BC) experimental system. Obvious energy transfer was observed without using a biased field in the sample, which proved that the PR effect exists in the material. At the same time, we calculated the 2BC net gain and the diffraction efficiency.Basing on CCD technology and software processing, we observed the holographic focusing effects of the material by use of the top-view method. The results showed that the material has holographic focusing effects at wavelenth of 632.8nm without using a biased field.At the end of the paper, we observed the solitons of this PR material and found the dissipative holographic solitons existed in the material. It showed that dissipative holographic solitons can exist in a two-beam dissipative system in a proper condition.