| Optical microcavities could confine light into a relative small area.When there exists a gain medium in the cavity,light intensity could be enhanced significantly by interacting with the gain medium during the propagation inside the cavity,resulting in stable standing wave oscillation and low-threshold lasing output.Compared with other microcavity structures such as Fabry-Perot(FP)and Photonic Crystal(PC)cavities,Whispering Gallery Mode(WGM)cavities,having unique advantages of ultrahigh Q factors and ultralow mode volume,have attacked much attention in both theoretical research areas such as cavity quantum electrodynamics(CQED)and practical applications areas such as sensing,detection,and filtering.WGM microcavities have rotational symmetrical structures,leading to isotropical emissions,which will unavoidably decrease the collection efficiency.In order to meet the demand in optoelectronic devices,such as enhancing the collection efficiency,increasing the integration degree of devices,improving the sensitivity and increasing working lifetime,the investigations on WGM-based deformed microcavities have largely increased.Traditional microcavity fabrication techniques such as UV lithography is mainly applied to planar microcavities and in the three-dimensional fabrication,they need to fabricate the sample in a layer-by-layer manner,which would seriously limit the choice of the shapes and the applications of three-dimensional deformed cavities.Recently,femtosecond laser processing has been gradually developed and become an effective method.With such method,micro/nano-scale devices can be precisely fabricated in a point-by-point way,giving rise to ultrahigh spatial resolution.This technique can be used for processing a wide range of materials.Therefore,this thesis is mainly devoted to the investigations on the fabrications of complicated three-dimensional deformed microcavities by femtosecond laser processing as well as the lasing properties of these microcavities.We adopt soft polymer photoresist with good chemical/biological compatibility and low cost as the host material and employed laser dye as the gain material which was doped into photoresist.Firstly,we fabricated,using self-assemble method,a metal hemisphere microcavity which produces WGM lasing emissions,and studied the effect of the coupling between the WGMs and metal SPP modes on the microcavity resonantmodes.Secondly,we fabricated,using femtosecond laser processing technique,a deformed spiral-shaped microcavity with a supporting pillar which results in lasing emissions with a low lasing threshold and unidirectional output.Thirdly,we fabricated complex and three-dimensional microcavities stacked with a deformed cavity and a WGM cavity by femtosecond laser processing technique and realized single-mode and unidirectional lasing emission by coupling the stacked two microcavities.Lastly,we investigated the possibility to remotely and rapidly fabricate micro/nano sturecutres,and produced porous microstructures by femtosecond laser filament processing,which result in broadband low-reflectivity black silicon surfaces.The main contents of the thesis are summarized as follows:1.We fabricated stable and smooth hemisphere microcavity on a hydrophobic substrate using a self-assemble method by balancing the surface tension and gravity of a droplet.The lasing spectrum measured at room temperature was found to originate from the WGM oscillating in the hemisphere microcavity.Furthermore,a thin silver film was covered on the hemisphere microcavity by vaccum evaporation resulting in a metal microcavity.Owing to the hybrid WGM and metal SPP modes in the metal cavity,the lasing modes showed a blue shift with an increased lasing threshold.Next,we theoreticely analyzed the influense of the covered silver film on the oscillating modes and spatial mode field distribution in the cavity.2.We fabricated,using femtosecond laser processing technique,a spiral-shaped disk microcavity with increasing curvature.By controlling the deformed factors,microcavities with different notch sizes were produced.By using a picosecond laser as a pumping source,we set up a sytem for pumping microcavities.We also set up a spectrometer detection system with which we detected the lasing spectrum emitted from the spiral disk with an initial radium of 15 ?m and notch size of 1 ?m,and obtained the lasing threshold.By measuring the intensity lasing emissions from different rotational directions of the microcavity,we obtained the far-field lasing intensity distribution,indicating that the spiral-disk microcavity can indeed produce the unidirectional lasing emissions from the notch.3.We fabricated different on-chip mircocavities directly on a high-reflection substrate via femtosecond laser processing.By comparing the lasing spectra and lasing threshold properties of a disk,ring,spiral-ring microcavities,we fabricated two different microcavities coupled vertically.By measuring the far-field distribution of the lasing emission,we found that the microcavities can produce unidirectionalemission from the notch.By analysing the lasing modes,Q factor and lasing threshold of the processed microcaivities,it was found that in the stacked microcavities the WGM cavity provides lasing oscillation and the spiral-ring cavity provides a unidirectional output.Meanwhile,only the modes that are resonant in both the cavities can be amplified.As a result,we produced a single-mode,low lasing threshold and unidirectional lasing output from the spiral-ring and ring coupled microcavity.4.We realized remote and rapid fabrication of mciro/nano structures on a silicon surface by using femtosecond laser filament.Porous and irregular distribution micro/nano-scale sturctures were produced on silicon surface by the ultrahigh light intensity in the plasma filament channel.During the interaction between filament and silicon surface,oxygen element and amourphous silica were induced on the surface,which increases significantly theabsorptance efficiency of sicon surface in a broadband range from 200 nm to 2500 nm.Similar micro/nano-scale structure was obtained resulting in a similar absorption by using different focal-length lens,indicating the rapidness,remote,stability and repeatability of femtosecond laser filament processing. |
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