Investigation On Optical Limiting Characteristics Of An Organometallic DMIT Compound

With the development of laser technology, various ultrafast laser appeared one after another. The power density of laser beam can easily reach hundreds of GW/cm2. On this condition, naked eyes are easy to get hurt and the optical detectors also easy to be damaged. In order to resolve this practical problem, the conception of laser protection is proposed. The development of optical limiting device for practical application becomes a problem that needs to be resolved urgently. The optical limiting devices of new generation are closely related with optical nonlinear materials. The optical limiting devices with excellent performance demand the nonlinear optical materials with high linear transmission, low nonlinear transmission, low optical limiting threshold, large cut-off intensity, large optical damage threshold, ultrafast response time and sufficient limiting band-with etc.. Although a large number of papers about nonlinear optical materials and its optical limiting properties are published in recent years, there still have a long way to find ideal nonlinear optical materials that can be used to make practical devices.In order to research nonlinear functional material with excellent performance which can use to make optical limiting devices, a kind of new organometallic DMIT compound [(C2H5)4N]2[Cu(dmit)2] (2 (tetraethylammonium) bis (4,5-disulfide bond in 1,3-dithiole-2-thione)-Cu; abbreviated as EtCu) was investigated. The molecular structure of DMIT materials hasπelectron-conjugation system. Delocalizedπelectrons can greatly strengthen the third-order nonlinear optical properties of DMIT materials. It's first time that the third-order nonlinear optical properties of EtCu are reported. By studying the optical limiting properties and analyzing the third-order nonlinear optical parameters of EtCu, we hope that we can provide basis for the design and synthesis of materials and provide accurate performance parameters for the production of optical limiting devices.My main work is as follows:Firstly, we synthesized a novel organometallic compound:EtCu and prepared it's solution in acetonitrile with concentration of 1.0×10-3 mol/L. We carried out its optical limiting experiment with different sample thickness under 18 ns laser pulse width at 1053 nm, observed its optical limiting curve and calculated its optical limiting threshold. The result suggests that EtCu has good optical limiting properties for nanosecond pulse in the near infrared band.Secondly, the detail deduction of Z-scan function, the method to measure nonlinear properties of material and the method to calculate nonlinear refractive index and nonlinear absorption coefficient were given.Thirdly, in order to study the nonlinear absorption properties of EtCu, we carried out open-aperture Z-scan experiment with 2mm sample thickness under 18ns laser pulse width at 1053nm. We observed its open-aperture Z-scan image, fitted its open-aperture Z-scan curve and calculated its nonlinear absorption coefficientβ. Using its open-aperture Z-scan image and fitting curve, we analyzed the optical limiting mechanism of EtCu. The result is that the optical limiting property of EtCu is caused by reverse saturable absorption (RSA).Lastly, using femtosecond-resolved optical Kerr gate method, we measured the nonlinear optical response time of EtCu/acetonitrile solution. The result shows that the response time is short, only 227fs.All the outcomes suggest that EtCu has potential applications in the optical limiting field.Our work is supported by the National Natural Science Foundation of P. R. China (Grant No.60778037 and No.50772059).