Fabrication And Characterization Of Whispering Gallery Mode Microlasers On Organic Crystals

Organic solid state lasers have attracted considerable attentions because theyhave potential to be tunable, flexible, biocompatible and easily integrated into plasticoptoelectronics. Optically pumped laser has been reported in a very broad range ofconjugated polymers and oligomers. However, for the electrically pumped organiclasers, there still exist many challenging problems to be resolved. One of them is thatthe organic devices have been damaged before the injected current reaches theexpected threshold current density (kA/cm2range) for electrically driven lasing due tothe low charge carrier mobilities of the disordered amorphous materials. In the viewof carrier transport and charge injection, single crystalline organic semiconductors arerecognized as potential building blocks for electrically pumped organic lasers. For alaser device, resonator structure is necessary to apply the positive optical feedback.However, since organic crystals are generally friable and sensitive to most organicsolution, there are still some challenges in the fabrication process. Lasers on organiccrystal has been little discussed.In this dissertation, whispering gallery mode(WGM) microlasers on organiccrystals will be made and characterized for the first time. In the fabrication process,firstly BP1T organic platy-monocrystal was grew with the method of physical vaportransport. Then a series of microdisks with specified sizes were formed on the crystalsby improved microfabrication technology and high quality BP1T WGM microlaserswere obtained.Photoluminescence of these microlasers were measured under the excitation of400nm pulse laser. With the appropriate period, a series of strong lasing emission hasbeen observed and the lasing threshold was measured. Then the size-dependence andstability of these microcavities were discussed in detail. Finally, through analysis and calculation of group refractive index, it can be seen that the positions of lasingemission peaks match the theoretical modes very well, which confirms the whisperinggallery mode lasing phenomenon.Thus, one important issue related application is when exposed to air, organicactive materials would lead to rapid degradation of the emission properties undereither optical or electrical excitation. Here, we present an appropriate encapsulationconfiguration for organic device protection is needed to ensure practicable lifetimes.We encapsulate organic whispering gallery mode optical microresonators withpolydimethylsiloxane (PDMS), and successfully achieved high stable lasing emissionwith high performance. The comparison of lasing properties demonstrates that thespectral properties of microlasers are not deformed when they are encapsulated inPDMS. Furthermore, the operational lifetime of lasers is doubly increased incomparison to the unencapsulated microlaser.