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.

In this paper, a ring laser design based on tapered waveguide coupler is fabricated and discussed. Using the asymmetric tapered waveguide coupler, two different directional coupling can be realized. Such that, the spatial-hole burning problem in linear laser cavity can be avoided, leading to the possibility of unidirectional traveling laser. In the work, two types of ring laser structures are fabricated and analyzed, in which (1) 90 degrees total reflection mirrors (TIMs) and (2) circular retro-mirrors are defined. Through the current injection on the tapered waveguide coupler, the received spontaneous emissions power at different directions (clockwise and counterclockwise directions) shows a 3dB difference for both type (1) and (2). Two oscillations in ring resonator could give different round-trip loss, indicating the possibility to fabricate unidirectional ring laser.

The goal of the thesis is Ring Laser Integrated Taper-directional Coupler Using Deep Etching to Fabricate Total Internal Reflection Mirrors. In order to total internal reflection, we make deep etching for the total reflection mirror. We use the tapered waveguide coupler, if unidirectional traveling-wave oscillation can be achieved, spatial hole burning effects seen in DFB laser can be avoided. In this paper, two types of ring laser structures are fabricated and discussed, in which (1) 90 degrees total reflection mirrors and (2) circular retro-mirrors. In fabrication process, we get smooth waveguide and highly perpendicularity waveguide by Self-Alignement wet etch method. In order to reduce bending loss and waveguide loss, we make deep etching for the total reflection mirror and circular retro-mirrors.

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

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.

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.

This thesis details the design and construction of an experiment to measure the radial distribution of laser gain in a cylindrical Helium-Neon laser gain tube. This distribution is important as it can effect the transverse mode structure of a running ring laser. Earlier theoretical models of the distribution were not supported by high quality experimental data and fail to take into account some physical processes. A resolution of 8 parts per million in gain and 50 μm in radial position has been achieved. Gain distributions have been measured and are shown to be well modeled by a 0th order Bessel function with first roots at the tube walls and a central dip depending on excitation power; except for the region very near to the tube walls where a very rapid increase in gain has been observed. Hydrogen has been identified by spectroscopic analysis as the primary constituent of gas contamination and cause of the long term reduction in gain of large ring lasers. Additional work has been done to detect a proposed non-classical Lense-Thirring field around a spinning lead superconductor. It was found that any effect is at least 20 times smaller than predicted. Techniques and tools for data acquisition programming have been reviewed focusing on difficulties with coupling of user interface and application logic, monolithicity, difficulties with scripting and algorithm implementation.

This thesis presents a study of a 1.6 metre square, helium-neon based ring laser gyroscope (denoted PR-1). This device is mounted on one of the internal walls of a high rise building. After optimisation a cavity Q of 2.9x10¹¹ and a sensitivity to rotation of approximately 10⁻³ of the background Earth bias was obtained. A detailed investigation of the single mode operating regime and multi-mode thresholds was undertaken and could be well accounted for with a simple model of the gain curves. A key feature of the operation of PR-1 is persistent longitudinal mode hopping. It is shown that by running the laser at selective high powers, one obtains CW mode locked operation thereby negating the influence of mode hopping and allowing for long time data acquisition. PR-1 was used to demonstrate oscillation of the Rutherford building on its second fundamental mode during an earthquake. In a separate investigation, a range of supermirrors were studied to determine the optimum configuration in a 4 by 4 metre ring laser. The set with the highest finesse prevailed despite the comparatively low light levels on the photo detectors. The geometric stability of the lasers was not found to be a significant factor.

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.