In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers.This single-frequency laser technology was used to develop an all-fiber actively Q-switched fiber lasers. A short cavity is used to create large spacing between longitudinal modes. Using this method, we demonstrated the first all-fiber Q-switched fiber laser in the 1 micron region.In addition to creating high peak powers with Q-switched lasers, created even higher powers using fiber amplifier systems. High power fiber lasers typically produce spectral broadening through the nonlinear effects of stimulated Raman scattering, stimulated Brullion scattering, and self-phase modulation. The thresholds for these nonlinearities scale inversely with intensity and length. Thus, we used a short phosphate fiber gain stage to reduce the length, and a large core fiber final stage to reduce intensity. In this way we were able to generate high peak power pulses while avoiding visible nonlinearities, and keeping a narrow bandwidth.The immediate goal of developing these high power fiber laser systems was to generate narrowband terahertz radiation. Two different wavelengths were combined into the final amplifier stage at orthogonal polarizations. These were collimated and directed into a GaSe crystal, which has a very high figure of merit for THz generation. The two wavelengths combined in the crystal through the process of nonlinear difference frequency generation. This produced a narrowband beam of THz pulses, at higher powers than previous narrowband THz pulses produced by eyesafe fiber lasers.

Para a espectroscopia de alta resolução e metrologia óptica em geral, é desejável um laser com linha espectral estável e de alta potência de saída para bombear diferentes tipos de ressonadores, como osciladores paramétricos óticos (OPO Optical Parametric Oscillator). Os lasers de frequência única disponíveis estão no alcance de potência de saída de 10 Watts, enquanto que, dependendo da aplicação e do tipo de OPO, é desejável uma maior potência (> 20 W). Neste trabalho foi desenvolvido um laser de frequência única e alta potência com base em módulos de bombeio por diodos e tendo como meio ativo o granada de alumínio de ítrio dopado com neodímio (Nd:YAG). Dois bastões de Nd:YAG bombeados transversalmente por diodo, foram utilizadas em uma configuração de ressonador em anel com saída polarizada de onda continua (CW continuous-wave), qualidade de feixe modo transversal eletromagnético (TEM00) e potência de saída de 105,2 W. A potência de saída alcançada é, a nosso entender, a mais alta para lasers em anel no modo fundamental transversal polarizado contínuo usando módulos Nd:YAG comuns com bombeamento lateral. O ressonador permitiu a sintonização de potência em uma grande faixa dinâmica e obteve excelente qualidade de feixe, usando uma placa de meia onda entre os dois bastões para compensação de birrefringência. A operação de frequência única foi alcançada usando cristal de granada de térbio-gálio (TGG-Terbium Gallium Garnet), dois imãs e um etalon, com uma potência de saída de 51,60 W e uma largura a meia altura da curva (FWHM) espectral de aproximadamente 17 MHz. / For high resolution spectroscopy, a high power, stable line output laser is desirable for pumping different types of optical parametric oscillator resonators (OPO). Single-frequency lasers are in the range of 10 watts of output power, while, depending on the application and the OPO type, higher power (> 20 W) is desirable. In this work a single frequency high power laser based on diode pumping modules with Nd:YAG as the active medium was developed. Two Nd:YAG bars transversally pumped by diodes were used in a configuration of a CW polarized ring resonator with beam quality TEM00 and output power of 105,2 W. The output power achieved is, to our knowledge, the highest for continuous polarized fundamental mode ring lasers using standard Nd:YAG modules with side pumping. The resonator allowed the tuning power in a large dynamic range and obtained excellent beam quality using a half-wave plate between the two rods for birefringence compensation. The single frequency operation was achieved using a TGG (Terbium Gallium Garnet) crystal, two magnets and an etalon, with an output power of 51.60 W and a 17 MHz full width at half maximum (FWHM) spectral width.