Abstract In this dissertation a rigorous analysis is performed on the reentrant non-planar ring laser cavity constructed by the Herriott-type multi-pass cell. Since the non-planar ring cavity is a non-orthogonal cavity, so the ABCD matrix method used to analyze the beam propagation is not valid. A rigorous method using Gaussian beam propagation is needed. The beam rotation, astigmatism, and spherical aberration are considered to obtain a self-consistent solution of the Gaussian beam. It turns out that spherical aberration is a very important issue for this non-planar resonator. Without taking into account the spherical aberration, a stable resonator would be difficult to realize. By using a self-consistent Gaussian beam propagation method, the characteristic of laser beam was analyzed and compared with that of the ABCD approximation method. The reentrant ring cavity is very sensitive to cavity length, especially when the planar and non-planar configurations have the same output beams; therefore, it is very important to consider a rigorous method using Gaussian beam propagation. By considering the coordinate transformation of the beam after mirror reflection, a non-planar figure-8 ring cavity can be treated as an orthogonal cavity except for an exchange of tangential and Sagittal planes after each reflection. A simple astigmatic Gaussian beam approach is used to analyze the non-planar figure-8 ring cavity, and an analytic solution is obtained. For the general case of the multi-pass non-planar ring cavity, a general astigmatic Gaussian beam approach is used to treat the problem. The general form of mirror phase shift is used, and two important differences compared to the ABCD method were found. Firstly, the spot size is always elliptical while the spot size is circular using the ABCD approximation. Secondly, a second stable region is found in the cavity, the width of the second stable region is smaller than the first stable regi

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.

A mode locked fiber-ring laser utilizing an optical spot-size converter (OSSC) integrated electroabsorption modulator (EAM) and Erbium-doped fiber amplifiers (EDFA) is demonstrated in this work. By taking advantage of OSSC, the EAMs not only have high-speed performance, but also have high tolerance alignment stability and high power handling capability due to the distributive effect. Thus, by the saturation absorbing and highly nonlinear transmission properties of such EAMs, it can be realized that short optical switching widow operations with high pulse energy excitation driven by EDFA can be used to hybrid mode locked ring laser application. The repetition rate of 10GHz in the mode locked fiber-ring laser is set by a RF synthesizer to driven EAM, creating short time gating widows. EDFA with an optical filter of bandwidth 1.2nm is used for optical gain. By adjusting the operation point in EAM to a bias of 1.72V and a RF-power of Vpp=2.2V, a nearly transform-limited autocorrelated Gauss pulse of 11.72ps (FWHM, the extracted pulsewidth is 8.28 ps) with average power level of 1.2mW is obtained. The time-bandwidth product is 0.478. The optical pulsewidths are mainly limited by the optical filter. Without any feedback circuit, pulse jitter of 993fs measured from a high-speed sampling scope (Agilent 86100A, bandwidth =30GHz) is found from the mode locked pulses, indicating the hybrid mode locked operation can be achieved by the EAM saturation absorbing properties. By measuring the photocurrent of EAM, the highest photocurrent occurs in the conditions of the highest optical transmission and also the shortest optical pulses, suggesting the saturation absorbing of EAM is the main mechanism dominating mode-lock operation. The mode locked operation with repetition rates of 10GHz to 20GHz are also obtained, indicating high-speed operation can be boosted from OSSC integrated EAM to hybrid-type mode locked fiber-ring laser.

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.

In the past thirty years, high power laser technology has been dominated by Nd:YAG as the gain medium. The pump wavelength of Nd:YAG is 808nm, and the lasing wavelength is 1064nm. It is categorized as four-level laser. The pump wavelength of Yb:YAG is 940nm, and the lasing wavelength is 1030nm. It falls into quasi-three-level laser category. Because Yb:YAG have higher quantum efficiency and less surplus heat, it have the potential to replace Nd:YAG. The purpose of this study is to develop a multi-reentrant two-mirror Yb:YAG ring laser. In this thesis, we will introduce multi-reentrant two-mirror ring laser. The thermal problem of quasi-three-level laser was overcome by multi-wavelength coating on gain medium and input/output couplers, numerical simulation for mode match, and efficient TE-cooling for laser crystal. This symmetrical two-mirror figure ¡§8¡¨ ring cavity has the merit of compact, few optical elements, and easy design. The 1030nm output laser of our ring cavity promises to make the design widely applicable to solid-state lasers, such as single longitudinal lasers and mode-locked lasers.

Diode laser pumped solid state laser is compact, and can generate high peak power laser with good output mode. It has been applied extensively in electronics, communication, and medical treatment in recent years. The purpose of this study is to develop a compact and practical ring laser system. The multi-reentrant ring laser system developed in this work composes of two spherical mirrors and a gain medium where the conventional ring laser systems have at least three mirrors to construct the laser cavity. The laser system is more compact and simple than conventional ring laser systems. It can be used for producing single frequency green and blue lasers. The laser system can also be applied in aviation, trace detection as well as compact picosecond mode-locked laser. We not only prove that the multi-reentrant laser system is feasible theoretically and experimentally, but also use the fundamental laser theory to find the relation among cavity length, number of points, number of circulation, and the distance between center of gain medium and optical axis. The exact solution we obtained is experimentally verified with good agreement. A comparison between exact solution and paraxial approximation is also performed. The beam paths observing from the top, side, and end view are analyzed for various multi-reentrant laser cavities. The stability of the cavity is numerically analyzed and experimentally verified with good agreement, too. Finally, the differences in cavity configuration between TEM01 mode and the figure-8 mode are compared in this thesis.

[pt] Esta dissertação de mestrado demonstra o princípio do funcionamento de um sistema gerador e multiplexador óptico utilizando pulsos curtos. Através do efeito de mode locked fiber ring laser pulsos curtos ópticos são gerados para taxa de repetição de 2.48 GHz ao passo que o escalonamento é atribuído ao uso de dispositivos passivos ópticos os quais compõem o conjunto experimental permitindo que a freqüência de 9.95 GHz seja atingida mediante a combinação exata das técnicas utilizadas. O coração de sistema está contido na geração e controle dos pulsos os quais determinarão a taxa de repetição em baixa freqüência e posteriormente a multiplexação através de linhas de atraso devidamente combinadas fornecerão o valor escalonado de operação de frequência. / [en] This master thesis demonstrates the principle of the functioning of an optical time domain multiplex system using short pulses. Through the effect of mode locked to fiber ring laser, optical short pulses are generated at repetition of 2.48 GHz to the step that the scheduling is attributed to the use of optic passive devices which compose the experimental setup allowing that the frequency of 9.95 GHz is reached by means of the accurate combination of the used techniques. The system heart is contained in the generation and control of the pulses which will later determine the rate of repetition in low frequency and multiplexing through lines of delay duly combined.

In the past three decades, Nd:YAG has been the dominating high power solid-state laser gain medium. Compared with Nd:YAG, Yb:YAG has lower quantum defects which produces less heat so that it can reduce thermo-optical deformation. In addition, the achieved doping concentration can be 100%, and the absorption FWHM at 941 nm is 18 nm. Based on above listed advantages, Yb:YAG has the potential to replace Nd:YAG. Using Yb:YAG as the laser gain medium in reentrant two-mirror laser cavity, we have succeeded in Yb:YAG ring laser and all the intracavity elements are coated by our electron gun deposition system. The main purpose of my research is to continue the previous result (slope efficiency: 20.1%), and further increasing the slope efficiency of our ring cavity with different round-trip transmittance of couplers. Besides, we measured and analyzed the polarization of the planar and non-planar ring cavities. At present, the highest slope efficiency we achieved is 38.9% with a round-trip transmittance of 16.4%.

Though Nd:YAG has been widely used as the traditional high power solid-state laser gain medium, Yb:YAG has more advantages such as lower quantum defect, wider absorption and emission bandwidth, and longer fluorescence lifetime, which can be used in Q-switched lasers to storage more energy. In addition, a higher doping concentration Yb:YAG with thinner thickness reduces the shift of optical path, which reduces the ring cavity stability. Therefore Yb:YAG is an eminently suitable gain medium for the two-mirror ring laser. Due to the quasi-three-level characteristic of Yb:YAG, the thermal effect influences the re-absorption loss and deteriorates the laser performance, i.e. lower slope efficiency of laser. In this thesis, we improve the laser efficiency by using Yb:YAG crystal with proper thickness, and various round-trip transmittances with different output couplers were tried. The slope efficiency with 50.3 % has been achieved. We also tried to reduce the thermal loading of Yb:YAG by crystal fiber with Cu-Al alloy package. The fabrication process of Yb:YAG crystal fiber, including sample preparation, and coating design, and the experiment result of Yb:YAG crystal fiber ring laser will be presented in detail. Furthermore, we use numerical analysis to modify the passively Q-switched Yb:YAG ring laser rate equation with FDTD (finite difference time domain) method. The simulated repetition rate, pulse width and peak power were compared to the experimental results in order to optimaize laser performance.

Semiconductor ring laser diodes (SLD) have been receiving attention for their potential use as source in photonic integrated circuits. Advantages of a ring laser include ease of integration because of no need for cleaved facets and they can be made very compact by folding their cavity . Ring laser have a unique feature, clockwise and counter- clockwise, in their lasing modes. If unidirectional traveling-wave oscillation can be achieved, spatial hole burning effects seen in Fabry-Perot and distributed feedback lasers can be avoided. In this work, the unidirectional oscillation is accomplished by controlling the taper shape structure. The whole laser cavity is formed using four reflection mirrors (TIR) and an output coupler passive waveguide. According to the Beam propagation Method (BPM) simulation, we find that the clockwise and counterclockwise oscillations have different behavior under various taper shape , indicating bidirectional oscillation can be eliminated. Moreover, bending loss¡Bmode transformation and optical gain are all included in calculation model. The waveguide is fabricated in the following steps: (1) ion implantation to get electrical isolation (2) selectively wet etching to form waveguide ridge (3) evaporation n- and p- electrode (4)spatter with Si3N4(5) planarization (6) evaporation microwave transmission line.