Because compact solid-state blue/green lasers can generate high power, and short wavelength radiation, it is applied in micromaching, laser display, underwater ranging, and so forth. It is a very cost-effective approach to develop such lasers, if the laser output characteristics can be estimated precisely using software simulation. The purpose of this study is to use an optics software GLAD (General Laser Analysis and Design) to model our intracavity frequency-doubled blue/green lasers. The GLAD software considers the wave nature of laser, such as dispersion and diffraction. Moreover, it employs a modular design in modeling linear or nonlinear optical components. In order to get more precised estimation of the laser output characteristics of a quasi-three-level laser, the laser model in GLAD was modified to take into account the reabsorption loss in gain medium. In our experiment, blue/green microchip lasers were developed. We used a 3W LD to pump a quasi-three-level laser with the Nd:YAG crystal as gain medium and KNbO3 crystal as the intracavity SHG crystal for the generation of blue laser. The laser generates 17.6 mW of blue power with a cavity length of 4 mm. With almost the same structure except using Nd:YVO4 crystal as gain medium and KTP crystal as the intracavity SHG crystal for generation of green laser, the laser produces 627 mW of green power with a cavity length of 6 mm.

O presente trabalho trata-se do desenvolvimento de uma cavidade Laser de estado sólido e geração de segundo harmônico, para fins oftalmológicos. A cavidade faz parte de um projeto maior que se refere a um fotocoagulador portátil, utilizado em diversos protocolos clínicos relacionados às doenças da retina e câmara anterior, como retinopatia diabética, retinopatia da prematuridade, glaucoma, edema macular e descolamento de retina. A cavidade proposta é composta por três espelhos dispostos em uma arquitetura em V. Um laser de diodo bombeia um cristal de Nd:YAG para a geração de laser em 1064nm que passa por um cristal de KTP para a geração de segundo harmônico em 532nm (laser verde). O sistema de acoplamento indexado à cavidade acopla até 90% da potência de saída em uma fibra óptica com núcleo de 100\'mü\'m. A cavidade projetada e implementada, produz um feixe com comprimento de onda de 532nm (laser verde), largura de banda de 0,5nm, potência máxima em torno de 2,5W na saída da fibra óptica e pulsos com duração máxima de 3s, que são requisitos para os tratamentos oftalmológicos associados a este tipo de equipamento. É importante destacar que a cavidade foi projetada e desenvolvida inteiramente com tecnologia nacional, sendo o primeiro trabalho desenvolvido no Brasil, que se tornou efetivamente um equipamento final para uso clínico. Além do projeto da cavidade laser, são descritos neste trabalho os sistemas mecânico e eletrônico, que possibilitaram seu funcionamento na integração do fotocoagulador. O fotocoagulador foi testado em pacientes voluntários da Escola Paulista de Medicina da UNIFESP, apresentando resultados comparáveis aos sistemas importados. / This work presents the research and the development of a solid state laser cavity with second harmonic generation for ophthalmological purpose. The laser cavity is part of a major project intended to produce a handle photocoagulator. This medical equipment is applied in several clinical protocols related to retinal and anterior chamber pathologies, such as diabetic retinopathy, retinopathy of prematurity, glaucoma, macular edema and retinal detachment. The present cavity is composed by three mirrors disposed in a V shape architecture. One laser diode pumps the Nd:YAG crystal to generate the 1064nm laser that is converted by second harmonic generation in 532nm through the KTP crystal (green laser). The coupling system attached in the cavity is able to collimate until 90% of the laser beam inside a optical fiber with 100 \'mü\'m core. The developed cavity produces a beam with wavelength of 532nm, spectral width of 0.5nm, maximum power around 2.5W in the end of the optical fiber and maximum pulse duration of 3s. Those parameters are requirements for ophthalmological treatments related to this kind of equipment. It is important to declare that the cavity was projected and developed in Brazil. This is the first work in this country that becomes effectively a device to clinical application. Besides the cavity design project, in this work also describes the mechanical and electronic sub systems that was responsible to the laser control and photocoagulator assembler. This product was tested in patients eyes from UNIFESP (Escola Paulista de Medicina), and showed similar results compared to the systems on the market.

O presente trabalho trata-se do desenvolvimento de uma cavidade Laser de estado sólido e geração de segundo harmônico, para fins oftalmológicos. A cavidade faz parte de um projeto maior que se refere a um fotocoagulador portátil, utilizado em diversos protocolos clínicos relacionados às doenças da retina e câmara anterior, como retinopatia diabética, retinopatia da prematuridade, glaucoma, edema macular e descolamento de retina. A cavidade proposta é composta por três espelhos dispostos em uma arquitetura em V. Um laser de diodo bombeia um cristal de Nd:YAG para a geração de laser em 1064nm que passa por um cristal de KTP para a geração de segundo harmônico em 532nm (laser verde). O sistema de acoplamento indexado à cavidade acopla até 90% da potência de saída em uma fibra óptica com núcleo de 100\'mü\'m. A cavidade projetada e implementada, produz um feixe com comprimento de onda de 532nm (laser verde), largura de banda de 0,5nm, potência máxima em torno de 2,5W na saída da fibra óptica e pulsos com duração máxima de 3s, que são requisitos para os tratamentos oftalmológicos associados a este tipo de equipamento. É importante destacar que a cavidade foi projetada e desenvolvida inteiramente com tecnologia nacional, sendo o primeiro trabalho desenvolvido no Brasil, que se tornou efetivamente um equipamento final para uso clínico. Além do projeto da cavidade laser, são descritos neste trabalho os sistemas mecânico e eletrônico, que possibilitaram seu funcionamento na integração do fotocoagulador. O fotocoagulador foi testado em pacientes voluntários da Escola Paulista de Medicina da UNIFESP, apresentando resultados comparáveis aos sistemas importados. / This work presents the research and the development of a solid state laser cavity with second harmonic generation for ophthalmological purpose. The laser cavity is part of a major project intended to produce a handle photocoagulator. This medical equipment is applied in several clinical protocols related to retinal and anterior chamber pathologies, such as diabetic retinopathy, retinopathy of prematurity, glaucoma, macular edema and retinal detachment. The present cavity is composed by three mirrors disposed in a V shape architecture. One laser diode pumps the Nd:YAG crystal to generate the 1064nm laser that is converted by second harmonic generation in 532nm through the KTP crystal (green laser). The coupling system attached in the cavity is able to collimate until 90% of the laser beam inside a optical fiber with 100 \'mü\'m core. The developed cavity produces a beam with wavelength of 532nm, spectral width of 0.5nm, maximum power around 2.5W in the end of the optical fiber and maximum pulse duration of 3s. Those parameters are requirements for ophthalmological treatments related to this kind of equipment. It is important to declare that the cavity was projected and developed in Brazil. This is the first work in this country that becomes effectively a device to clinical application. Besides the cavity design project, in this work also describes the mechanical and electronic sub systems that was responsible to the laser control and photocoagulator assembler. This product was tested in patients eyes from UNIFESP (Escola Paulista de Medicina), and showed similar results compared to the systems on the market.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18281号 / 工博第3873号 / 新制||工||1594(附属図書館) / 31139 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 藤田 静雄, 准教授 須田 淳 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

<p>This study examined the self-trapping of light emitted by a miniature green laser in a photopolymerizable medium and the interactions between two parallel-propagating self-trapped beams. The work included the design and fabrication of an Intra-Cavity Frequency-Doubling (IC-FD) Nd: YVO₄/MgO: PPLN miniature green laser with a stable and tunable output intensity. Emission from this laser enabled a systematic examination of self-trapping phenomena at incident intensities spanning 8 orders of magnitude (3.2× W·cm^-2to 6368 W·cm^-2). When launched into a photopolymerizable medium, light emitted by the miniature green laser self-trapped by initiating polymerization and corresponding changes in refractive index along its propagation path. The evolution and dynamics of the self-trapped beam corresponded to the behaviour of self-trapped beams of coherent light. Interactions between a pair of parallel-propagating self-trapped beams were also characterised at a range of intensities. This study shows that the miniature green laser is an efficient, coherent source with a large range of output intensities for the excitation of self-trapped beams. This opens opportunities for its incorporation into small-scale optical systems designed to operate based on the generation and interactions of self-trapped beams.</p> / Master of Applied Science (MASc)

Abstract Single frequency laser has the advantages of high stability in frequency and low noise. Therefore, single frequency laser is now widely used in applications, such as high precision measurement, holography and data storage. Attempts to generate second harmonic radiation using a linear cavity have typically resulted in significant amplitude fluctuations due to longitudinal mode coupling. Various techniques have been proposed for solving the so called ¡§green problem¡¨ to achieve single longitudinal mode operation, such as inserting optical component in the conventional linear cavity or use ring cavity instead of linear cavity. Uni-directional ring cavity has shown to be the most robust method for producing single frequency laser. The purpose of this study is to develop compact and low-cost single frequency IR and green lasers. A novel symmetrical two-mirror figure ¡§8¡¨ ring cavity is developed. Instead of using several laser mirrors for beam deflection, this ring laser system employs only two spherical mirrors to form the laser cavity for traveling wave oscillation and eliminates ¡§spatial hole burning¡¨ caused by the standing wave operation. In this thesis, we use two-mirror figure ¡§8¡¨ ring cavity for the generation of single frequency IR and green lasers. The polarization status is crucial for high efficient intracavity frequency doubling. The polarization evaluation in a nonplanar and reentrant ring cavity is characterized by measuring the thermally induced linear and circular birefringence and analyzing the polarization rotation due to cavity configuration. We have demonstrated a 2-mirror figure ¡§8¡¨ ring cavity which is compact and has few optical elements. The stable single frequency laser output of our ring cavity promises to make the design widely applicable to solid-state lasers.

Purpose To evaluate the effectiveness and safety of Selective Laser Trabeculoplasty (SLT) with the SLT mode of the VISULAS ® green laser in patients with primary open-angle glaucoma (POAG). Methods This prospective, interventional multicenter clinical investigation included patients with POAG who either needed a treatment escalation because the individual intraocular pressure (IOP) target was not met or treatment initiation and had an IOP ≥ 17 mmHg at baseline in the study eye. The study was conducted in five research centers across Germany. Approximately 100 laser applications were delivered to 360° of the trabecular meshwork. Glaucoma medications were not modified during the 3-month follow-up to allow evaluation of the sole effect of VISULAS ® green with SLT. Efficacy outcomes were postoperatively absolute and relative IOP changes at 1 and 3 months. Safety outcomes analyzed the rate of intra- and postoperative adverse events. Results Thirty-four eyes of 34 POAG patients were included. The overall mean number of preoperative glaucoma medications was 2.2 ± 1.4 in 29 treated eyes, 5 eyes were treatment naïve. Mean baseline IOP (mmHg) was 21.0 ± 2.69 and was reduced by − 3.53 ± 3.34 [95% CI − 4.61; − 2.45] and − 3.59 ± 3.41 [95% CI − 4.64; − 2.53] at the 1- and 3-month follow-up, respectively (p < 0.0001), with 48.5% of cases achieving a ≥ 20% IOP reduction at 3 months [95% CI = 30.8%; 66.5%]. The mean relative IOP reduction was − 16.4% and − 16.3% at 1 and 3 months, respectively (p < 0.0001). Potentially device- or procedure-related adverse events were mild to moderate and included 3 postoperative IOP-spikes and 6 reports regarding eye pain and discomfort. All were resolved without sequelae. Conclusions SLT performed with the VISULAS ® green laser achieved clinically significant additional IOP reductions in medically treated as well as in treatment naïve eyes with POAG and there were no relevant safety issues. The results are comparable to other reported SLT studies.

L’utilisation des semi-conducteurs à large bande interdite (wide bandgap ou WBG) tels que le carbure de silicium SiC, le nitrure de gallium GaN, le diamant, etc… s’est répandue dans le domaine de l’électronique de puissance ces dernières décennies. Leurs caractéristiques électroniques et mécaniques font des WBGs des solutions alternatives pour remplacer le traditionnel silicium. Cependant, des études supplémentaires sont indispensables pour améliorer la tenue en tension, les pertes statiques et dynamiques et les performances en fonctionnement à haute température des composants WBGs. Dans ce cadre, deux bancs expérimentaux OBIC (Optical Beam Induced Current) spécifiques « en cours de développement » sont mis en place pendant cette thèse. L’OBIC consiste à éclairer avec un faisceau laser de longueur d’onde appropriée une jonction polarisée en inverse, des porteurs de charge sont alors créés par absorption photonique. On peut alors mesurer un courant induit par faisceau optique (OBIC) lorsque les porteurs sont générés dans la zone de charge d’espace. Après une première phase de préparation et d’adaptation de l’environnement expérimental, des essais ont mené à la démonstration du principe de génération multi-photonique en éclairant une jonction SiC avec un faisceau vert (532 nm). L’analyse des différentes mesures OBIC nous a permis de construire une image du champ électrique à la surface de la diode : une analyse non destructive pour étudier l’efficacité des protections périphériques des jonctions et pour détecter les défauts dans la structure cristalline. Egalement, la durée de vie des porteurs minoritaires a été déduite par l’analyse de la décroissance du courant OBIC au bord de la jonction. Les coefficients d’ionisation sont également déterminés par la méthode OBIC, ces coefficients sont des paramètres clés pour la prévision de la tension de claquage des composants. Nous avons réalisé des mesures OBIC dans le GaN, et nous avons observé un effet d’absorption bi-photonique dans le diamant avec un faisceau UV (349 nm). / In the last few decades, the use of wide bandgap (WBG) semiconductors (silicon carbide SiC, gallium nitride GaN, diamond, etc…) has become popular in the domain of power electronics. Their electronic and mechanical characteristics made of the WBGs a good alternative to the traditional silicon. However, additional studies are mandatory to improve the breakdown voltage, static and dynamic losses, and the performance at high temperature of the WBG devices. In this context, two specific experimental benches OBIC (Optical Beam Induced Current) -under development- are set up during this thesis. OBIC method consists to generate free charge carriers in a reverse biased junction by illuminating the device with an appropriate wavelength. An OBIC signal is measured if the charge carriers are generated in the space charge region. After a first phase of preparation and adaptation of the experimental environment, OBIC measurements led to demonstrate the multi-photonic generation by illuminating a SiC junction with a green laser (532 nm). OBIC measurements allowed giving an image of the electric field at the surface of the diode: OBIC presents a non-destructive analysis to study the efficiency of the peripheral protection and to detect the defects in the semi-conductor. Minority carrier lifetime was also deduced by studying the OBIC decrease at the edge of the space charge region. Ionization rates were extracted using OBIC method; these coefficients are key parameters to predict the breakdown voltage of the devices. OBIC measurements were also realized on the GaN, and two-photon generation was highlighted by measuring an OBIC current in the diamond when illuminating it with a UV laser beam (349 nm).