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In recent years, there has been a growing interest towards compact high peak-power pulsed laser sources for applications such as LIDAR, range findings, remote sensing, communications and material processing. A common laser architecture used to realize these sources is the Master Oscillator Power Amplifier (MOPA), in which a master oscillator produces a highly coherent beam and a fiber amplifier boosts the output power, while preserving its main spectral properties. Phosphate glasses are recognized to be an ideal host material for engineering the amplification stage of a pulsed MOPA since they enable extremely high doping levels of rare-earth ions to be incorporated in the glass matrix without clustering, thus allowing the fabrication of compact active devices with high gain per unit length. With the aim of realizing compact optical fiber amplifiers operating at 1 and 1.5 µm, a series of highly Yb3+- and Yb3+/Er3+-doped custom phosphate glass compositions were designed and fabricated to be used as active materials for the core of the amplifiers. Suitable cladding glass compositions were explored and final core/cladding glass pairs were selected to realize single-mode and multi-mode optical fibers. Core and cladding glasses were synthesized by melt-quenching technique. The core glass was then cast into a cylindrical mold to form a rod, while the cladding glass was shaped into a tube by rotational casting method or extrusion technique. The latter has been extensively employed for the manufacturing of tellurite and germanate glass preforms, but only recently the first example of active phosphate fiber preform fabricated by this method has been reported by our research team. Phosphate fibers were then manufactured by preform drawing, with the preform being obtained by the rod-in-tube technique. Preliminary results of pulsed optical amplification at 1 and 1.5 µm are presented for a single-stage MOPA.

Motivada per la creixent demanda d'aplicació dels làsers de potència mitjana / pic alta a 2 micres, aquesta tesi doctoral està dedicada a desenvolupar un amplificador criogènic multipàs a 2 micres en règim de nanosegons basat en la ceràmica transparent Tm: Y2O3. Per assolir aquest objectiu, es va estudiar a fons la ceràmica transparent Tm: Y2O3 com a mitjà actiu i es va emprar el concepte d'amplificador de potència d'oscil·lador mestre (master oscillator power amplifier) per desenvolupar el sistema làser criogènic. Aquest treball es divideix en 7 capítols. El capítol 1 presenta l'estat actual dels làsers polsats a 2 micres, així com la motivació i els objectius d'aquesta tesi. Els capítols 2, 3 i 4 descriuen les caracteritzacions de l'medi actiu (ceràmica transparent Tm: Y2O3) en termes d'estructura de l'material, espectroscòpia criogènica i potencial làser en ona contínua. A partir d'aquests estudis, es van obtenir paràmetres crucials en el disseny de l'làser, com la longitud d'ona exacta de bombament / làser, la vida mitjana de l'nivell emissor, el factor de guany, etc. El capítol 5 presenta la demostració d'un oscil·lador mestre (master oscillator), que va servir com a font llavor per a l'etapa de l'amplificador. El capítol 6 mostra l'escalat en energia a través de l'amplificador de pas múltiple en dues geometries diferents. A la fin, el capítol 7 resumeix els resultats obtinguts i projecta la investigació futura. Motivada por la creciente demanda de aplicación de los láseres de potencia media / pico alta a 2 μm, esta tesis doctoral está dedicada a desarrollar un amplificador criogénico multipaso a 2 μm en régimen de nanosegundos basado en la cerámica transparente Tm:Y2O3. Para alcanzar este objetivo, se estudió a fondo la cerámica transparente Tm:Y2O3 como medio activo y se empleó el concepto de amplificador de potencia de oscilador maestro (master oscillator power amplifier) para desarrollar el sistema láser criogénico. Este trabajo se divide en 7 capítulos. El capítulo 1 presenta el estado actual de los láseres pulsados a 2 μm, así como la motivación y los objetivos de esta tesis. Los capítulos 2, 3 y 4 describen las caracterizaciones del medio activo (cerámica transparente Tm:Y2O3) en términos de estructura del material, espectroscopía criogénica y potencial láser en onda continua. A partir de esos estudios, se obtuvieron parámetros cruciales en el diseño del láser, como la longitud de onda exacta de bombeo / láser, la vida media del nivel emisor, el factor de ganancia, etc. El capítulo 5 presenta la demostración de un oscilador maestro (master oscillator), que sirvió como fuente semilla para la etapa del amplificador. El capítulo 6 muestra el escalado en energía a través del amplificador de paso múltiple en dos geometrías diferentes. Al final, el capítulo 7 resume los resultados obtenidos y proyecta la investigación futura. Motivated by the increasing application demands on the 2 μm high average/peak power lasers, this thesis is devoted to develop a cryogenic 2 μm multi-pass amplifier in the nanosecond regime based on the Tm:Y2O3 transparent ceramics. To reach this goal, the active medium Tm:Y2O3 transparent ceramic was well studied and the master oscillator power amplifier concept was employed for developing the cryogenic laser system. This work is divided into 7 chapters. Chapter 1 introduces the current state-of-the-art of the 2 μm pulsed lasers as well as the motivation and objectives of this dissertation. Chapters 2, 3 and 4 describe the characterization of the active medium Tm:Y2O3 transparent ceramic in terms of material structure, cryogenic spectroscopy, and continuous-wave lasing potential, respectively. From those studies, crucial laser design parameters, such as the exact pump/lasing wavelength, lifetime, gain factor, etc., were obtained. Chapter 5 presents the demonstration of a master oscillator, which served as the seed source for the amplifier stage. Chapter 6 shows the energy scaling via the multi-pass amplifier in two different geometries. Finally, chapter 7 summarizes the achieved results and outlooks the future research.

For a high power 1064 nm nanosecond MOPA pulse fibre laser, the seeding pulse shape is distorted after amplified by pre-amplifier and power-amplifier stages under the effect of gain saturation. As the pulse shape is crucial for some industrial applications, the distortion of eight different shapes of seeding pulses is experimentally studied, and the Stimulated Raman Scattering (SRS) for several shapes is also investigated. Published version

We report on the design and preliminary development of a micro laser (MILD) breadboard (BB). The laser source is designed to be used as the transmitter unit of a laser altimeter for planetary investigations. The reference scenario is the ESA BepiColombo mission to Mercury (presently scheduled to be launched in 2012) but possible applications to minor solar system bodies may be included. In order to fulfil the laser source requirements for this kind of application we adopted a master-oscillator-power-amplifier (MOPA) scheme. Analysis of the MO efficiency, pulse duration and beam characterisation in different resonator configurations is described together with the preliminary PA performance on a ±10 æC temperature range.

A custom fabrication procedure for pump combiners matched to a wide variety of double-clad fibers used in high power fiber lasers has been developed. Both combiners with and without feedthrough can be fabricated with an improved repeatability thanks to a specific mechanical setup that simplifies placing the fibers in their proper location within the input bundle before the tapering and fusion processes. Extensive characterization results on 7-to-1 and on (6+1)-to-1 combiners are confirming the validity of the proposed approach.

We explore the use of quantum cascade structures as amplifiers for terahertz radiation. For this purpose, two section devices were fabricated, in which the output from a nu similar to 2.3 THz laser section is amplified in a subsequent stage. For relatively short devices we obtain an amplification of 1.5x, in good agreement with the calculated level. Based on these results we predict that amplifications of up to 13 dB could be obtained for such structures using increased amplifier lengths of a few millimeters.(C) 2007 American Institute of Physics.