Optical Coupling between LD Bar and Optical Fiber and Study on Characteristics of LD Pumped Passively Q-switched Mode-locked Laser
|Keywords||Fiber coupling Laser diode-pumped Rate-equation model Q-switched and mode-locked laser Intensity fluctuation mechanism|
Laser-diode (LD) pumped solid-state lasers have wide applications in the fields such as laser telecommunication, remote-sensing detection, materials processing, information processing, medical, as well as military due to its advantages such as all solid state, small volume, high pump efficiency, high beam quality, long longevity, high stability and various running modes,and have been focused much attention on.High-power laser diode arrays (LDA for short) have advantages such as high photo-electric conversion efficiency, small size, high power, high reliability, simple structure and so on. LD lasers have been widely used in applications, the technical level of materials and devices has also been greatly improved. However, laser diode arrays have their inherent disadvantages. The beam quality of a typical one-dimensional line of laser diode arrays in the vertical and parallel to the PN junction is very different, which is a limit for their further applications. In order to improve beam quality of laser diode arrays and reduce the beam divergence, it is essential for shaping the output beam to form a high-brightness fiber-coupled diode laser output with small core diameter and small numerical aperture.Meanwhile, the fiber can achieve flexible transmission, and made the use of them more convenient.Laser crystal is the core component in laser system. Its optical and physical properties determine the global design and output characteristics of the laser system. And the Nd-doped crystals due to their excellent lasing property at 808nm and availability of direct laser diode pumping have been widely used to construct laser-diode pumped solid-state lasers in the near-infrared region.In this dissertation, considering beam characteristics of the diode lasers and LD arrays, we developed a high efficient high-power fiber coupling modules. By using micro-optical elements (BTS and HOC), the beams from 19 light-emitting unit of a high-power laser diode bar whose width is lcm and light-emitting area thickness about 1nm into a single optical fiber with core diameter of 400μm and NA=0.22.And the coupling efficiency is 72%. By using the fiber-coupled laser-diode as the pump source, Nd:LuVO4 crystals as the gain mediums, we have performed the passively Q-switched mode-locked (QML) laser operation at 1.06pm with SESAM.And we studied the theoretical and experimental performance of the passively Q-switched mode-locked (QML) lasers with SESAM, respectively. The pulse width, the repetition rate and pulse peak power under different incident pump power are measured. Meanwhile, by considering the population-inversion density in the gain medium, the ground-state population density of saturable absorber and the influence of the pump rate, the rate equations of a LD-pumped passively Q-switched mode-locked Nd:LuVO4 laser at 1.064μm with SESAM are given. The theoretical average output power, pulse width, and pulse repetition of the laser are obtained by the numerical solution of the rate equations, and the theoretical calculations agree with the experimental results of passively Q-switched mode-locked laser.