The multi-pass ring cavity was constructed using only a pair of identical spherical mirrors, which is compact and can easily be aligned. The spatial hole burning effect and green problem can be eliminated in these ring cavities that can be applied to generate a single frequency laser. The characteristics of multi-pass non-planar and planar multi-pass ring cavities were analyzed, such as the reentrant conditions and cavity stability. The multi-pass ring lasers were successfully demonstrated by the reentrant condition simulations, the cavity length error between experimental result and simulation value were below 1.2%. Yb3+:YAG was used as the gain medium in this dissertation, it has many advantages compared with that of Nd3+:YAG. Such as high doping concentration, low quantum defect, long upper state lifetime, broad emission bandwidth and its wide absorption band. However, the quasi-three-level nature of Yb3+:YAG makes temperature control crucial for laser performance. A Ti:sapphire laser pumped Yb3+:YAG bulk crystal multi-pass continuous-wave ring laser was demonstrated with a slope efficiency of 50.3%, and a Yb3+:YAG crystal fiber ring laser was demonstrated with a slope efficiency of 54.7%. The thermal load in Yb3+:YAG was observed and compared with that of Nd3+:YAG. The passively Q-switched operation was obtained by a Cr4+:YAG saturable absorber. Due to the ring cavity configuration, the spontaneous noise from gain medium perturbs the population difference of the saturable absorber was reduced so that the timing jitter of the repetition period was restrained to around 11% while 33 ns pulses were obtained. A compact diode-pumped continuous-wave ring cavity with 25.0% slope efficiency was presented. Two main challenges are noticed in the high power laser diode end pumped configuration, mode-matching difficulty and huge heat load. The mode-matching problem can be solved by an appropriate cavity design, the laser-heated pedestal growth (LHPG) method was used to growth Yb3+:YAG crystal fiber with small surface to improve the heat dissipation. The fiber crystal laser was successfully generated and compared with that of bulk crystal. To our knowledge, this is the first demonstration of a Yb3+:YAG ring laser, and also the first demonstration of Yb3+:YAG crystal fiber ring laser.

Abstract We use InGaAlAs and InGaAsP as materials of 1.55mm multi-quantum-well spot-size converter ridge waveguide lasers. On lateral conversion, we fabricate a taper ridge waveguide. On vertical conversion, we add guard layers on each side of active layer. For InGaAlAs ridge waveguide lasers, simulation results show a far field 16o ¡Ñ 27o¡]lateral ¡Ñ vertical¡^at guard layer width S = 0.1 mm with 300-150-50 mm narrow-tapered waveguide structure. Due to large Zn background contamination in the MOCVD growth chamber, we did not fabricate the InGaAlAs lasers successfully. For the InGaAsP ridge waveguide lasers, we measure a far field 18o ¡Ñ 28o and a threshold current 23 mA for the 200-250-50 mm narrow-tapered waveguide structure; a far field 20o ¡Ñ 26o and a threshold current 22 mA for the 200-250-50 mm wide-tapered waveguide structure.

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.

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(blue) 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, low-cost and high-efficiency single frequency IR, green and blue lasers. To continue our preview achievement in single frequency IR and green laser systems, shorter wavelength for 946 nm and blue (473 nm) single frequency laser were attempted. In this thesis, we introduced how could only two spherical mirrors to form the laser cavity for traveling wave oscillation and eliminate ¡§spatial hole burning¡¨ caused by the standing wave operation. And we overcome the thermal problem of quasi-three-level laser by multi-wavelength coating on gain medium and input/output couplers, numerical simulation for mode match, and TE-cooling system for laser crystal. Finally, a non-planar figure ¡§8¡¨ 946-nm ring laser were developed using the multi-reentrant ring cavity, and controlled beam path at uni-directional operation. This symmetrical two-mirror figure ¡§8¡¨ ring cavity has the merit of compact, few optical elements, and easy design. The stable single frequency laser output of our ring cavity promises to make the design widely applicable to solid-state lasers.

The Raman Injection Laser is a new type of laser which is based on triply resonant stimulated Raman scattering between quantum confined states within the active region of a Quantum Cascade Laser that serves as an internal optical pump. The Raman Injection Laser is driven electrically and no external laser pump is required. Triple resonance leads to an enhancement of orders of magnitude in the Raman gain, high conversion efficiency and low threshold. We studied this new type of laser and conclude some basic equations. With reasonable experimental parameters, we calculated the laser gain, losses and the output power of the Raman Injection Laser by using Mathematica and FEMLab. Finally we compared the theoretical and experimental results.

Femtosecond laser microsurgery has emerged as a remarkable technique for precise ablation of biological systems with minimal damage to their surrounding tissues. The combination of this technique with nonlinear optical imaging provides a means of microscopic visualization to guide such surgery in situ. A clinical endoscope capable of image-guided femtosecond laser microsurgery will provide physicians a means for cellular-level microsurgery with the highest precision. This dissertation focuses the development of a miniaturized fiber-coupled probe for image-guided microsurgery, towards future realization as a clinical endoscope. The first part of the dissertation describes the development of an 18-mm diameter probe. This development includes delivery of femtosecond laser pulses with pulse energy in excess of 1 µJ through air-core photonic bandgap fiber, laser beam scanning by a microelectromechanical system scanning mirror, and development of a new image reconstruction methodology for extracting increased temporal information during Lissajous beam scanning. During testing, the 18-mm probe compares favorably with the state-of-the-art as a microscopic imaging tool and we present the first known demonstration of cellular femtosecond laser microsurgery through an optical fiber. The second part of the dissertation explores further refinement of the design into a streamlined package with 9.6 mm diameter and improved imaging resolution. Study of the optical performance through analytical and computer-aided optical design indicates that simple custom lenses can be designed that require only commercial-grade manufacturing tolerances while still producing a fully aberration-corrected microsurgical endoscope. With the 9.6-mm probe, we demonstrate nonlinear optical imaging, including tissue imaging of intrinsic signals from collagen, using average laser powers 2-3× lower than the current state-of-the-art. We also demonstrate the use of the 9.6-mm probe in conjunction with gold nanoparticles for enhanced imaging and microsurgery through plasmonics. Finally, in the third part of this dissertation, we detail bench-top development of a new clinical application for combined femtosecond laser microsurgery and nonlinear optical imaging: the treatment of scarred vocal folds. We show the utility of femtosecond laser microsurgery for creating sub-epithelial voids in vocal fold tissue that can be useful for enhancing localization of injectable biomaterial treatments. We demonstrate that a single compact fiber laser system can be utilized for both microsurgery and imaging. Furthermore, the proposed clinical technique is shown to be achievable with parameters (e.g., pulse energy, focused spot size) that were found to be attainable with fiber-coupled probes while still achieving ablation speeds practical for clinical use. / text

No description available.

A wide band linearly chirped erbium-doped fiber laser has been developed. The erbium-doped fiber laser using a rotating mirror/grating combination as one of the reflectors in a Fabry-Perot laser cavity has been tuned over a 46 nm spectral range. Linearization of the chirp rate has been achieved using feedback from a fiber Fabry-Perot interferometer (FFPI) to adjust the voltage ramp which drives the rotating mirror. In a demonstration of monitoring an array of two fiber Bragg grating (FBG) sensors, a wavelength resolution of 1.7 pm has been achieved. The linearly chirped fiber laser has been used in measuring the optical path difference (OPD) of interferometric fiber optic sensors by performing a Fourier transform of the optical signal. Multiplexing of an array of three FFPI sensors of different lengths has been demonstrated, with an OPD resolution ranging from 3.6 nm to 6.3 nm. Temperature was measured with one of the sensors over the range from 20°C to 610°C with a resolution of 0.02°C. Short FBGs are used to form the two mirrors of a fiber Bragg grating pair interferometer (FBGPI) sensor, so that the mirror reflectances change gradually as a function of temperature. Modulating the drive current of a DFB laser produces chirping of the laser frequency to scan over ~2.5 fringes of the FBGPI reflectance spectrum. Because the fringes are distinguished due to the FBG reflectance change, the ambient temperature can be determined over the range from 24 oC to 367 oC with a resolution of 0.004 oC. Multiplexing of FBGPI sensors of different lengths with a linearly chirped fiber laser has demonstrated improved sensitivity and multiplexing capacity over a conventional FBG WDM system. The FBG spectral peak position and the phase shift of an FBGPI are determined through the convolution of the sensor reflected signal with an appropriately matched reference waveform, even though the reflectance spectra for the FBGs from different sensors overlap over a wide temperature range. A spectral resolution for the FBG reflectance peak of 0.045 GHz (0.36 pm), corresponding to a temperature resolution of 0.035 oC, has been achieved.

A ring laser gyroscope (gyro) is an active laser interferometer designed to sense rotation through the Sagnac frequency shift encountered by two beams travelling in opposite directions around a closed path. The classes of devices considered in this thesis are the large and ultra-large ring laser gyros. These instruments are designed for direct measurement of earth rotation rate and find applications in geodesy, geophysics, and tests of physical theories. The research presented in this thesis focuses on the demonstration of new techniques for operating ring laser gyros. The main goal of these techniques has been the correction for variations in the geometry of an ultra-large ring laser gyro, UG-3. This instrument is a 77 m perimeter ultra-large ring laser gyro of heterolithic construction and is the primary instrument used in the experiments presented here. UG-3 has been used to demonstrate measurement of earth strains which have been used to correct for changes in the geometry of the instrument. It has also been used to demonstrate a control technique where the co-rotating beams were alternately offset allowing the number of wavelengths around the perimeter to be counted and a Sagnac rotation signal to be obtained. Among the most important outcomes of this research of interest to the large ring laser gyro community is that we now understand most of the problems that would affect a next generation ring laser gyro. This understanding allows us to choose an operational technique best suited to the measurements being made and thus maximise the scientific potential of the instrument. Additionally, the development of a new standard for data storage and an associated suite of software to acquire, query and analyse ring laser data is expected to improve collaboration with the wider research community. Other research outcomes of more general interest include the analysis of how oscillation of a single mode is established in a high finesse laser cavity. We demonstrate that the ultimate mode of operation can be selected with a ‘seed’ beam of exceptionally low intensity. An interesting related outcome is the demonstration of Sagnac beat frequency measurement during the ring down of a ring cavity, a type of measurement immune to dispersive and flow related frequency shifts.

Cette thèse a pour objet d'améliorer la connaissance du mécanisme de formation de suie. Deux méthodes ont été utilisées pour produire des particules de suie dans des conditions contrôlées : le brûleur à flamme plat où les particules se forment par combustion de mélanges d'éthylène/air riches et le tube à choc dans lequel la suie est produite par pyrolyse de C2H4 à haute pression (5 bar) et dans un large domaine de température (1850-2100 K). Ces deux systèmes ont été équipés avec un dispositif original de diffusion laser à trois angles couplé à l'extinction laser pour suivre la croissance de particules, identifier les différentes étapes de leur mécanisme de formation et en déduire l'évolution de la fraction volumique des suies, leur rendement, leur structure et leur morphologie. Dans la flamme, l'addition de H2 entraîne une réduction globale de la concentration des suies, de leur diamètre moyen des particules et leurs agglomérats, de la densité en nombre de particules. Dans le tube à choc, on n'observe pas de dépendance significative du délai d'induction à la formation des particules par addition de H2. La courbe de rendement en suie en fonction de la température présente la même forme avec et sans hydrogène mais le rendement maximal est fortement abaissé en présence d'hydrogène pour une concentration initiale fixée en atomes de carbone. Le rôle de l'hydrogène sur la croissance des particules et les caractéristiques des suies est discuté en comparant les résultats obtenus dans le cas de la flamme de prémélange et derrière l'onde de choc réfléchie respectivement.