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Steady-state and Femtosecond Dynamics of High Order Optical Nonlinearities in A New Inorganic-organic Nanocomposite Material Highly Dispersed with Semiconductor CdSe Quantum Dots


 

演讲人:Pro. Yasuo Tomita,  Department of Electronics, University of Electro-Communications, Tokyo, Japan
时间:2018年12月4日(周二)14:00-16:00
地点:电院SEIEE 5-214

 

 

Abstract:

 

Photopolymerizable nanocomposite materials, the so-called photopolymerizable nanoparticle-polymer composites (NPCs), can record multi-dimensional photonic lattice structures by holographic assembly of nanoparticles in polymer. We have developed various types of such NPCs for versatile applications in photonics and neutron optics. When nanoparticles with large optical nonlinearities are employed, NPCs can be used for a new type of nonlinear optical nanocomposite materials. In this work we report on the fabrication and the nonlinear optical characterization of a semiconductor CdSe quantum dots (QDs) dispersed NPC film at the doping concentration of CdSe QDs as high as ~7 vol.%. The film can be both uniformly and holographically cured by green light. Open and closed Z-scan measurements, degenerate multi-wave mixing and femtosecond pump-probe and transient grating measurements are conducted. It is found that the observed fifth-order optical nonlinearity has the cascaded third-order contribution that becomes significant at high doping concentrations of CdSe QDs. We describe a generic closed Z-scan theory for nonlinear optical materials possessing both saturable absorption and high order/saturable nonlinear refraction, useful for the analysis of our nonlinear optical measurements. It is also shown that there are picosecond-scale intensity-dependent and nanosecond-scale intensity-independent decay components in the nonlinear refraction and transparency data. The former is caused by the Auger process as observed in colloidal CdSe QDs, while the latter comes from the electron-hole recombination process.

 

Biography:

 

Yasuo Tomita received the B.E. and M.E. degrees both from Hokkaido University, Sapporo, Japan, in 1978 and 1980, respectively, and the M.S. and Ph.D. degrees both from California Institute of Technology, Pasadena, USA  in 1986 and 1989, respectively. Since 2001 he is a professor at the University of Electro-Communications, Tokyo, Japan. He is fellow of SPIE, OSA and the Japan Society of Applied Physics (JSAP). His current research interests include photonic nanocomposite materials, nonlinear optics, neutron optics and information photonics.

 

 

 

 

联系人:邹卫文

 

 

 

 

 

 
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