The Construction Of Organic Lasing Microcavity And Its Application In Humidity Sensing

In recent years,with the development of device miniaturization and integrated technologies,optical microcavities have shown great potential in basic research and application areas.Optical microcavity is those cavities with dimension of optical wavelength in one direction at least.It confines light inside a small volume by total internal reflection at the interface.As the volume of cavity is decreased to micro size,only one or several optical modes can exist inside the resonator.The optical confinement provided by a microcavity greatly enhances the interaction between optical spatial mode and the light emitting materials.Among these microcavities,whispering gallery mode microcavities have been widely applied in sensing areas because of their high Q factors and small mode volume.However,the study of whispering gallery mode sensor is mainly concentrated in the field of passive cavity.From the application point of view,the detection schemes of most solid WGM sensors usually adopt tapered fibers or prism coupling configurations,which are bulky and difficult to apply in the micro-and nanoscale sample environments.Conventional fabrication of microresonators adopting semiconductor processing technology(top-down approach)still faces some challenges.Owning to good self-assembly property,organic materials can form regular shapes through low cost and simple solution self-assembly method.Moreover,active resonators containing a gain medium,allow remote excitation and collection of the WGM-modulated fluorescence spectra,which is more suitable in sensing.Based on the above research background,organic spherical whispering-gallery mode(WGM)microcavities and belt-shaped Fabry-Perot(F-P)microcavities were fabricated by solution self-assembly method.Meanwhile,whispering gallery mode microcavities were applied in humidity sensing areas,mainly including the following three aspects:(1)Polystyrene(PS)microspheres doped with an organic dye DCM were prepared by an emulsion solvent evaporation method.The size of the microspheres is between1-10 microns.The surface of the microspheres is smooth and has a good sphericity.Using the femtosecond laser as the pump light source to study the laser characteristics of the microspheres,the microspheres exhibited good whispering gallery mode lasing in the band of the 600-630 nm,the threshold of the microsphere is 3.8 W/cm~2,and the quality factor is 3035.To further study the lasing behaviors,FDTD simulation was employed to simulate the optical field distributions of optical mode in the microcavities.The size dependent simulated radiation have also been studied.Using the advantages of good compatibility of polystyrene and organic gain media,Coumarin 6 and DSO-TF were introduced into the microspheres to achieve stimulated emission in the green and blue bands.(2)The organic DSO-TF microbelts were obtained by the solution self-assembly method and the length is between 1-10 microns.Under the excitation of 325 nm femtosecond laser,the organic microbelts exhibited good Fabry-Perot lasing in the band of the 430-440 nm.The threshold of the microbelt is 24.8 W/cm~2 and the quality factor is 2169.(3)WGM cavities and their resonant wavelengths are inherently sensitive to the surrounding environment.A microsphere was applied in humidity sensing.As the relative humidity changed from 0 to 97%,the mode shifted 0.59 nm.The sensitivity was 6 pm/RH%,and the sensing mechanism was analyzed.