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.

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.

[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%.

Compared with Nd:YAG, the traditional high power solid state laser gain medium, Yb:YAG has less quantum defect, no excited state absorption, and longer fluorescence lifetime, which makes it suitable for Q-switched laser. In addition, concentration quenching is absent in Yb:YAG, higher concentration of active ion makes the thickness of gain medium thinner. For ring cavities, the necessity of symmetrical beam path is important, a thinner Yb:YAG crystal can reduce the shift of optical beam path and avoids cavity unstability. Thus, Yb:YAG is suitable for the two-mirror ring cavity. In this study, a compact and efficient Yb:YAG ring laser with 50.3% slope efficiency was demonstrated. And the Yb:YAG ring laser performances influenced by thermal effect was analyzed and compared to that of Nd:YAG ring laser. The polarization of ring lasers with different configurations were also discussed. In manufacturing process, the coating design on gain medium and laser mirrors were introduced. The advantages of passively Q-switched laser are efficient, compact, simple setup and no complicated driving circuits. They make passively Q-switched laser suitable for various applications, such as nonlinear optics, medical treatment, micromachining, material processing, and range finder. Due to spontaneous noise from the gain medium, conventional passively Q-switched laser has large timing jitter. This study is to build up a passively Q-switched Yb:YAG/Cr4+:YAG ring laser with lower timing jitter. At present, a Q-switched ring laser with a peak power of 208 W and a pulse width of 33 ns, was developed. Its slope efficiency is 18.1% with a timing jitter of 11.9%. To our knowledge, this is the first passively Q-switched Yb:YAG/Cr4+:YAG ring laser.

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.

Ringlaser dienen dazu, durch genaue inertiale Messungen Rotationen ohne Bezug auf ein externes Referenzsystem lokal und praktisch in Echtzeit zu bestimmen. Sie wurden in den 1970er Jahren insbesondere für die Navigation von Flugzeugen entwickelt. In den letzten Jahrzehnten wurden Ringlaser dann so weit verbessert, dass sie nun auch als eigenständige Messinstrumente in der Geodäsie Verwendung finden. Aufgrund der erreichbaren Genauigkeit ist es inzwischen möglich, Variationen in der Erdrotation mit der dafür erforderlichen Präzision zu detektieren. Der stabilste unter den Ringlasern, der so genannte Ringlaser "G" der geodätischen Fundamentalstation Wettzell, erreicht eine Sensitivität von 1.2 x 10 -11 nrad. Damit ist dieses Instrument in der Lage, Neigungen von bis zu 1 nrad (dies entspricht einem Signal von 0.2 mas in der Polbewegung, in Änderung der Rotationsgeschwindigkeit der Erde) im täglichen und halb-täglichen Frequenzband zu messen. Motivation dieser Arbeit ist es, der in den letzten Jahren erreichten Verbesserung des Auflösungsvermögens und der Sensorstabilität Rechnung zu tragen und die für die Auswertung von Ringlaserdaten benutzten geophysikalischen Modelle weiter zu verbessern, um dadurch die variable Rotation der Erde noch präziser vermessen zu können. Die dafür relevanten Effekte werden in den einzelnen Kapiteln dieser Arbeit separat behandelt. Nach einer Einführung werden in Kapitel 2 dieser Arbeit drei lokale, topozentrische Koordinatensysteme konstruiert, mit welchen sich das zu beobachtende Sagnac-Signal eines Ringlasers in der ersten post-Newtonischen Näherung der Allgemeinen Relativitätstheorie adäquat beschrieben lässt. In Kapitel 3 wird ein verbessertes Modell für die Orientierung des Ringlasers, basierend auf Ergebnissen von Dehant et al. (1999), entwickelt. Ein in den bislang benutzten Modellen vernachlässigter Neigungsterm konnte dabei identifiziert werden. Ein Modell für die retrograde tägliche Polbewegung der Erde wird in Kapitel 4 entwickelt. Ausgehend von den dynamischen Gleichungen für eine starre Erde werden diese um elastische Effekte und Einflüsse der Mehrschichtigkeit der Erde ergänzt und die entsprechenden Euler-Liouvilleschen Gleichungen und Transfer-Funktionen abgeleitet. Gezeiteneinflüsse des Ozeans, speziell die dadurch hervorgerufene sub-tägliche Variation der Erdrotation und ozeanische Auflasteffekte, werden in Kapitel 5 behandelt. Es wird gezeigt, dass die ozeanischen Signale größer als 10 -9 Δf0 (Δf0 348 Hz für den Ringlaser "G") sind und damit in den Messdaten des Ringlasers "G" nachweisbar sein sollten. Auf Grundlage der in dieser Arbeit entwickelten Modelle wurde eine 168 Tage (30. April 17. Oktober 2010) umfassenden Datenreihe des Ringlasers "G" in Kapitel 6 ausgewertet. Für die Auswertung wurde die Software ETERNA 3.40 genutzt und entsprechend angepasst. Die tägliche retrograde Polbewegung konnte dabei mit einer Genauigkeit von 0.15 mas bestimmt werden. Diese Auswertung beweist ein weiteres Mal die Existenz eines flüssigen Erdkerns. Des weiteren konnte gezeigt werden, dass bestimmte Gezeitenparameter des halb-täglichen Frequenzbandes durch lokale Effekte beeinflusst werden. Lokal gemessene Luftdruckdaten wurden benutzt, um den Einfluss atmosphärischer Auflasteffekte auf den Ringlaser "G" zu untersuchen. Die Ergebnisse dieser Arbeit zeigen, dass sich für diese Effekte kein signifikanter Einfluss nachweisen lässt. Die Arbeit schließt mit einer Zusammenfassung der Resultate, einer Beschreibung der sich ergebenden Schlussfolgerungen und einem Ausblick auf zukünftige Arbeiten auf dem Gebiet der Ringlaseranalyse. / Ring laser gyroscopes measure inertial rotations locally and in real-time without the need for an external reference system. Initially, they were developed for aircraft navigation applications in the 1970s. With the improvement of ring laser technology during the last decades large ring laser gyroscopes (RLGs) are nowadays used as independent geodetic instruments. Due to the achievable accuracy more and more geophysical signals become observable in the data. The G-ring located at the Geodetic Observatory Wettzell is reckoned as the most stable one amongst the running large RLGs and reaches a sensitivity of 1.2 x 10 -11 nrad. Therefore, the instrument is able to detect a tilt signal of 1 nrad (equivalent to a signal of 0.2 mas in polar motion or 10 -9 Ω0 in variation of Earth rotation rate) in the diurnal and semi-diurnal band. This motivates us to improve previous geophysical models and estimate associated tilt and Earth rotation signals, which are the focuses of this Thesis. Firstly, we construct three local proper topocentric reference frames and interpret the Sagnac effect observed by large RLGs in the first post-Newtonian (PN) approximation of Einstein's theory of gravity. Secondly, in Chapter 3 we develop an improved orientation model for the Sagnac platform, based on the numerical results of Dehant et al. (1999). A missing tilt term in previous RLG tilt models is found. In Chapter 4, based on the Euler-Liouville equations or nutation transfer functions for a rigid Earth, a purely elastic Earth, a two-layered Earth and a three-layered Earth, five retrograde diurnal polar motion models are computed with the HW95 tidal potential catalogue. Thirdly, ocean tide effects (two aspects: effects on sub-daily variations of Earth rotation and loading effect on tilt) are considered in Chapter 5. We show that the Sagnac signals induced by ocean tides are larger than 10 -9 Δf0 (Δf0 348 Hz for the G-ring) and their influences are visible in the G-ring. Fourthly, based on the above-mentioned improved models and 168 days (from Apr.30 to Oct.17 in 2010) of G-ring data, in the diurnal band, we estimate the retrograde diurnal polar motion signal with an accuracy of 0.15 mas. The Earth tide software ETERNA 3.40 was adopted and modified to analyse this data. Our estimation provides one more evidence for the existence of the Earth's fluid outer core. Furthermore, we found that the tidal parameters for the G-ring are affected by the cavity and topographic effects in the semi-diurnal band. The local air pressure record is used in order to investigate the atmospheric loading effect on the G-ring by a simple regression model. Nevertheless, the preliminary result shows that no significant influence from atmospheric loading on our estimation is found. This Thesis closes with a summary of the obtained results, conclusions and suggestions how the analysis of ring laser data could be improved in future work.

Ringlaser dienen dazu, durch genaue inertiale Messungen Rotationen ohne Bezug auf ein externes Referenzsystem lokal und praktisch in Echtzeit zu bestimmen. Sie wurden in den 1970er Jahren insbesondere für die Navigation von Flugzeugen entwickelt. In den letzten Jahrzehnten wurden Ringlaser dann so weit verbessert, dass sie nun auch als eigenständige Messinstrumente in der Geodäsie Verwendung finden. Aufgrund der erreichbaren Genauigkeit ist es inzwischen möglich, Variationen in der Erdrotation mit der dafür erforderlichen Präzision zu detektieren. Der stabilste unter den Ringlasern, der so genannte Ringlaser "G" der geodätischen Fundamentalstation Wettzell, erreicht eine Sensitivität von 1.2 x 10 -11 nrad. Damit ist dieses Instrument in der Lage, Neigungen von bis zu 1 nrad (dies entspricht einem Signal von 0.2 mas in der Polbewegung, in Änderung der Rotationsgeschwindigkeit der Erde) im täglichen und halb-täglichen Frequenzband zu messen. Motivation dieser Arbeit ist es, der in den letzten Jahren erreichten Verbesserung des Auflösungsvermögens und der Sensorstabilität Rechnung zu tragen und die für die Auswertung von Ringlaserdaten benutzten geophysikalischen Modelle weiter zu verbessern, um dadurch die variable Rotation der Erde noch präziser vermessen zu können. Die dafür relevanten Effekte werden in den einzelnen Kapiteln dieser Arbeit separat behandelt. Nach einer Einführung werden in Kapitel 2 dieser Arbeit drei lokale, topozentrische Koordinatensysteme konstruiert, mit welchen sich das zu beobachtende Sagnac-Signal eines Ringlasers in der ersten post-Newtonischen Näherung der Allgemeinen Relativitätstheorie adäquat beschrieben lässt. In Kapitel 3 wird ein verbessertes Modell für die Orientierung des Ringlasers, basierend auf Ergebnissen von Dehant et al. (1999), entwickelt. Ein in den bislang benutzten Modellen vernachlässigter Neigungsterm konnte dabei identifiziert werden. Ein Modell für die retrograde tägliche Polbewegung der Erde wird in Kapitel 4 entwickelt. Ausgehend von den dynamischen Gleichungen für eine starre Erde werden diese um elastische Effekte und Einflüsse der Mehrschichtigkeit der Erde ergänzt und die entsprechenden Euler-Liouvilleschen Gleichungen und Transfer-Funktionen abgeleitet. Gezeiteneinflüsse des Ozeans, speziell die dadurch hervorgerufene sub-tägliche Variation der Erdrotation und ozeanische Auflasteffekte, werden in Kapitel 5 behandelt. Es wird gezeigt, dass die ozeanischen Signale größer als 10 -9 Δf0 (Δf0 348 Hz für den Ringlaser "G") sind und damit in den Messdaten des Ringlasers "G" nachweisbar sein sollten. Auf Grundlage der in dieser Arbeit entwickelten Modelle wurde eine 168 Tage (30. April 17. Oktober 2010) umfassenden Datenreihe des Ringlasers "G" in Kapitel 6 ausgewertet. Für die Auswertung wurde die Software ETERNA 3.40 genutzt und entsprechend angepasst. Die tägliche retrograde Polbewegung konnte dabei mit einer Genauigkeit von 0.15 mas bestimmt werden. Diese Auswertung beweist ein weiteres Mal die Existenz eines flüssigen Erdkerns. Des weiteren konnte gezeigt werden, dass bestimmte Gezeitenparameter des halb-täglichen Frequenzbandes durch lokale Effekte beeinflusst werden. Lokal gemessene Luftdruckdaten wurden benutzt, um den Einfluss atmosphärischer Auflasteffekte auf den Ringlaser "G" zu untersuchen. Die Ergebnisse dieser Arbeit zeigen, dass sich für diese Effekte kein signifikanter Einfluss nachweisen lässt. Die Arbeit schließt mit einer Zusammenfassung der Resultate, einer Beschreibung der sich ergebenden Schlussfolgerungen und einem Ausblick auf zukünftige Arbeiten auf dem Gebiet der Ringlaseranalyse. / Ring laser gyroscopes measure inertial rotations locally and in real-time without the need for an external reference system. Initially, they were developed for aircraft navigation applications in the 1970s. With the improvement of ring laser technology during the last decades large ring laser gyroscopes (RLGs) are nowadays used as independent geodetic instruments. Due to the achievable accuracy more and more geophysical signals become observable in the data. The G-ring located at the Geodetic Observatory Wettzell is reckoned as the most stable one amongst the running large RLGs and reaches a sensitivity of 1.2 x 10 -11 nrad. Therefore, the instrument is able to detect a tilt signal of 1 nrad (equivalent to a signal of 0.2 mas in polar motion or 10 -9 Ω0 in variation of Earth rotation rate) in the diurnal and semi-diurnal band. This motivates us to improve previous geophysical models and estimate associated tilt and Earth rotation signals, which are the focuses of this Thesis. Firstly, we construct three local proper topocentric reference frames and interpret the Sagnac effect observed by large RLGs in the first post-Newtonian (PN) approximation of Einstein's theory of gravity. Secondly, in Chapter 3 we develop an improved orientation model for the Sagnac platform, based on the numerical results of Dehant et al. (1999). A missing tilt term in previous RLG tilt models is found. In Chapter 4, based on the Euler-Liouville equations or nutation transfer functions for a rigid Earth, a purely elastic Earth, a two-layered Earth and a three-layered Earth, five retrograde diurnal polar motion models are computed with the HW95 tidal potential catalogue. Thirdly, ocean tide effects (two aspects: effects on sub-daily variations of Earth rotation and loading effect on tilt) are considered in Chapter 5. We show that the Sagnac signals induced by ocean tides are larger than 10 -9 Δf0 (Δf0 348 Hz for the G-ring) and their influences are visible in the G-ring. Fourthly, based on the above-mentioned improved models and 168 days (from Apr.30 to Oct.17 in 2010) of G-ring data, in the diurnal band, we estimate the retrograde diurnal polar motion signal with an accuracy of 0.15 mas. The Earth tide software ETERNA 3.40 was adopted and modified to analyse this data. Our estimation provides one more evidence for the existence of the Earth's fluid outer core. Furthermore, we found that the tidal parameters for the G-ring are affected by the cavity and topographic effects in the semi-diurnal band. The local air pressure record is used in order to investigate the atmospheric loading effect on the G-ring by a simple regression model. Nevertheless, the preliminary result shows that no significant influence from atmospheric loading on our estimation is found. This Thesis closes with a summary of the obtained results, conclusions and suggestions how the analysis of ring laser data could be improved in future work.