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Micro-photoluminescence And Nonlinear Effects In Dielectric Crystalline Optical Waveguides And Nanoparticles

Posted on:2013-02-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:N N DongFull Text:PDF
GTID:1118330374980617Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Optical waveguides are micro-structured regions with high refractive index surrounded by low refractive index areas. Optical waveguides can confine light propagation within structures to dimensions of the order of several microns, reaching very high optical intensities. The investigation of micro-photoluminescence and nonlinear effects in waveguide structures is of great importance for the realization of photonic devices, such as waveguide laser or second harmonic generation (SHG). Compact optical circuits can be realized by the integration of a couple of photonic devices in a single waveguide platform. As a result, optical systems with high miniaturization, stabilization and good performance can be achieved. As the basic components, the quality of optical waveguides affects the function of integrated photonic circuits. Therefore, the fabrication of high quality optical waveguide structures is the basis of integrated photonic circuits, and has bocome one of the most significant research topics in integrated optics/photonics and modern optical communications.As of yet, several methods have been employed to manufacture optical waveguides, including energentic ion beam irradiation, femtosecond laser inscription, ion exchange, diffusion and thin film deposition, etc. Energentic ion beam irradiation and femtosecond laser inscription have attracted great attention owing to their advantages of convenience, fast, no pollution to the environment and super applicability for most of optical materials. According to the different irradiation approaches, energentic ion beams can be divided into ion implantation, swift heavy ion irradiation and focused ion beam writing. As one mature material surface modification technology, ion implantation has becoming one of the most promising techniques to fabricate waveguides in more than100optical materials including crystals, transparent ceramics, glasses, semiconductors and polymers, etc. For traditional light-ion implantation, usually only consisits of hydrogen (H) and helium (He) ions, the incident ions will collide with the target ions and a low refractive index optical "barrier" layer will be formed at the end of the ions'track due to the nuclear energy deposition. During the ion trajectory, the incident ions mainly collide with electrons of the target atoms and produce ionization, and induce slight variation of the refractive index. As a consequence, the regions between the material surface and the optical barrier are waveguide volumes. Swift heavy ion irradiation usually adopts heavy ions with atomic number above8and energies above1MeV/amu. In these cases, the electronic damage is dominant over the nuclear collisions during most of the ion trajectory. Depending on the amorphous nano-track induced by single ion irradiation or the overlapping of heavy lattice damage induced by multiple ions irradiation, the refractive index will change and effective waveguide structures will be formed at lower fluences. Focused ion beam writing is a unique direct-writing method to fabricate2D waveguides beneath sample surface. During the process, focused ion beams, with diameters from a few microns to submicrometric scales, are irradiated into the substarte at specific depth beneath the sample surface and then induce refractive index changes. Typically, the ions are protons or He ions. Femtosecond laser inscription adopts near-infrared femtosecond laser with high optical densities as the writing source. In these cases, optical materials can absorb two or more photons, and structure changes are produced owing to the avalanche ionization. In the meantime, the refractive index of the materials in the irradiated regions will change and optical waveguides are constructed. Femtosecond laser inscription possesses the advantages of fast, clean, high spatial resolution, superior applicability to various materials, and has been increasing used for waveguide fabrication.Over the last years, bio-imaging techniques have experienced countless developments, especially due to the requirements of biomedical research and clinical treatment. In particular, the combination of ultrafast laser oscillators, confocal microscopy, and biocompatible fluorescent nanoparticles has emerged as a powerful tool for high-resolution cellular and tissue imaging. The discovery of novel fluorescent probes is a key research subject. Lanthanide-doped upconverting nanoparticles (UCNPs) are attracting considerable attention. These nanoparticles can be multiphoton excited with near infrared (NIR) light to generate emission at higher energies spanning from UV to NIR. What is important, the NIR range700-900nm is the "biological window" where the tissue has little absorption and scattering to the light. As a result, UCNPs can be used for deeper detection. Comparing with quantum dots (QDs) and organic fluorescent materials, UCNPs have some advantages of high chemical stability, high optical conversion efficiency, low toxicity, high singal-to-noise ratio. In addition, near-infrared laser source is cheap and can produce high power. With all these merits, UCNPs are going to exerting important impacts on bio-imaging.In this dissertation, we report on the fabrication of planar, channel or cladding waveguides by using ion implantation, swift heavy ion irradiation and femtosecond laser inscription in variety of optical materials, including KTP crystals, Nd3+:YAB crystals, Nd3+:YVO4+KTP hybrid system, Nd3+:MgO:LiNbO3crystals, Yb3+:YAG ceramics, and Nd3+:Y2O3ceramics. The prism coupling and end-face coupling were introduced to analyse the dark modes, near-field intensity distributions and propagation losses. Thermal annealing treatments were used to improve the propagation properties. The refractive index profiles were reconstructed by combining SRIM (the stopping and ranges of ions in matter) and RCM (reflectivity calculation method). Based on the reconstructed refractive index distributions, FD-BPM (finite difference beam propagation method) was used to simulate the near-field intensity distributions. Confocal microscopy was employed to measure the micro-fluorescence, Raman or SHG properties in order to investigate the structure modifications in the waveguide regions. Based on the end-face setup, waveguide SHG experiments were performed in self-frequency or frequency crystals. Comparing CaF2:Er3+,Yb3+and CaF2:Tm3+,Yb3+these two kinds UCNPs, their potential applications in bio-imaging were analysed.Potassium titanyl phosphate (KTiOPO4or KTP) is a widely used nonlinear crystal for phase-matched frequency doubling (particularly efficient under1064→532nm SHG). We report on the birefringent phase-matching SHG in nonlinear KTP buried channel waveguides produced by femtosecond laser inscription with the so-called "double-line" configuration. The stable SH green light at~532nm with peak power0.15kW has been achieved with the pulsed~1064nm fundamental laser pumping, with the maximum optical conversion efficiency of~11%. Under the continuous wave pump configuration, the maximum power of the generated532nm light is~49μW with a conversion efficiency of0.016%.We report on the efficient SHG at532nm from femtosecond laser inscribed KTP cladding waveguide structures in configuration of birefringent phase matching. The guiding structures, with cross section areas of~104μm2, are with circular and hexagonal boundaries, respectively, and guided in any transverse direction. Under1064nm pulsed fundamental beam pump, the conversion efficiency of the SH green lasers from the waveguides are as high as45%, indicating the fabricated buried channel waveguides could be good candidates for green laser source.We report on the micro-Second Harmonic (u-SH) and micro-Raman (μ-Raman) images of ion implanted channel and planar waveguides in KTP crystals. The μ-SH images reveal that the nonlinear properties in the waveguides have not been deteriorated during the implantation process. This is consistent with the μ-Raman images that lattice distortions are minimal at waveguide's volume. Both the structural and nonlinear properties of the KTP lattice have been only modified at the end of ions' trajectory, which is in good agreement with the positions with maximum refractive index changes.Neodymium doped yttrium aluminum borate (Nd3+:YAl3(BO3)4or Nd3+:YAB) crystal is one good self-frequency-douling laser crystal which combines the good thermal, mechanical, and nonlinear properties of the YAB host with the outstanding fluorescence properties of Nd ions. Buried channel optical waveguides, supporting both magnetic (TM) and transverse (TE) polarizations, have been fabricated in a Nd3+:YAB crystal by ultrafast laser inscription following the so-called "double line" approach. Confocal fluorescence and SH imaging experiments have revealed that the original fluorescence and nonlinear properties have been not deteriorated by the waveguide inscription procedure. Preliminary laser experiments have shown the ability of the fabricated structures for green laser light generation under808nm optical pumping by self-frequency-doubling of the1.06μm laser line of neodymium ions. Green output powers close to40μW has been achieved.Neodymium doped yttrium orthovanadate (Nd3+:YVO4) crystal is an efficient IR laser crystal owing to its outstanding features of high emission cross section, broad absorption bands, good mechanical and thermal properties. We report on the fabrication of optical channel waveguides supporting both visible and infrared TE and TM confinement in a hybrid system composed by a Nd3+:YVO4laser gain medium glued to a KTP nonlinear crystal by ultrafast laser inscription. The micro-photoluminescence and second harmonic confocal images of the fabricated waveguides have revealed that the laser and nonlinear properties of the constituent crystals have been not deteriorated due to the waveguide inscription. The resulting structures emerge as promising candidates for the development of multi-frequency waveguide lasers.Lithium niobate (LiNbO3) is a multi-functional material for the combination of the excellent electro-optic, acousto-optic, photoelastic, photorefractive and nonlinear optic properties. Neodymium doped lithium niobate (Nd3+:MgO:LiNbO3) is a widely used laser medium. We report on the fabrication of optical channel waveguides produced in Nd3+:MgO:LiNbO3crystals by hydrogen (H), carbon (C), and oxygen (O) ions implantation. The micro-luminescence investigations indicate that the fluorescence properties in the waveguide regions are well preserved comparing with the bulks. The ion implantation induced lattice distortions translate from the nuclear damage region (NIR) to the electronic damage region (EDR) when the ion mass is increased (from H to O). The C ion implanted wavegudes exhibit hybrid fluorescence properties of both H and O ions implanted waveguides.We report on the fabrication of Nd3+:MgO:LiNbO3active planar waveguides based on the generation of non-overlapping nano-tracks by ultralow-fluence swift Ar ions irradiation. The analysis of the micro-photoluminescence (μ-PL) have shown that the fluorescence efficiency of Nd3+ions have been well preserved in the waveguides with respect to bulk, thus making the waveguides good candidates for integrated laser sources. More interestingly, the presence of a relevant distortion of the LN network in the surroundings of the amorphous tracks has been determined from the analysis of the induced shifts in both the Nd3+luminescence and Raman modes. It has been concluded that the creation of non-overlapping amorphous tracks leads not only to a partial amorphization of the lattice network but also to a relevant lattice compression in their surroundings, which suggests that the final refractive index modification is the consequence of the interplay between both effects. Finally, it has been found that the presence of ion induced nano-tracks leads to a strongly enhanced SH signal, which is tentatively attributed to the associated lattice modifications (damage, disorder and distortions).Ytterbium doped aluminium garnet (Yb3+:YAG) ceramic is one novel laser gain medium. We report on the fabrication of carbon (C) ion implanted channel waveguides in a Yb3+:YAG ceramic. The resulting waveguides have shown good optical properties with well-confined and nonleaking propagation modes and with moderate propagation losses. We have found that the use of medium mass avoids the activation of fluorescence quenching.Neodymium doped yttria (Nd3+:Y2O3) ceramic is an attractive laser gain medium which possesses high melting point, high thermal conductivity and excellent laser performance. We report on the Nd3+:Y2O3ceramic optical channel waveguides produced by femtosecond laser inscription with a "double-line" scheme. The confocal μ-PL images reveal that the original fluorescence emission properties have not been affected by the laser filamentation, which means the original luminescence features have been well preserved in the waveguide volumes. The fabricated micro-photonic structures emerge as promising candidates for integrated laser sources.Very recently, lanthanide doped CaF2UCNPs have gained recognition due to their good infrared-to-visible upconversion fluorescence efficiencies. We report on the remarkable two-photon excited fluorescence efficiency of CaF2:Tm3+,Yb3+nanoparticles in the "biological window". Based on the strong Tm3+ion emission (at around800nm), tissue penetration depths as large as2mm have been demonstrated, which are more than four times those achievable based on the visible emissions in comparable CaF2:Er3+,Yb3+nanoparticles. The outstanding penetration depth, the absence of cytotoxicity in the incubated cells, together with the fluorescence thermal sensitivity demonstrated here, makes CaF2:Tm3+,Yb3+nanoparticles ideal candidates as multifunctional nanoprobes for high contrast and highly penetrating in vivo fluorescence imaging applications.
Keywords/Search Tags:Optical waveguides, Ion implantation, Swift heavy ion irradiation, Femtosecond laser inscription, Secnond harmonic generation, Photoluminescence, Raman, Upconverting nanoparticles
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