Ultrafast Multi-GHz Waveguide Lasers

在这项工作中，我们将开发非常紧凑和高效的激光源，其占地面积仅为几平方厘米，每秒能够产生超过10亿个光脉冲，每个脉冲的持续时间小于万亿分之一秒的十分之一。这种光源有着广泛的应用，包括生物细胞的显微镜检查、光学频率的精确测量、光谱学和电信，这些都可以利用脉冲的非常短的持续时间和其高重复率。这些应用中的许多目前依赖于大型且相对低效的激光器，这必然限制了应用设计。我们提出的激光源是基于波导几何形状，将激光限制在非常小的尺寸，类似于玻璃光纤中使用的方式。然而，这些波导是基于晶体，如掺钛蓝宝石和掺镱钨酸盐，它们已经证明自己能够提供我们感兴趣的非常短的光脉冲。波导几何形状还能够支持集成到一个单片器件中的组件，该器件既可以用作产生光所需的激光增益材料，又可以提供给出短脉冲所需的超快切换。波导将通过在未掺杂的衬底上生长掺杂晶体的薄层来制造，掺杂剂提供激光增益和将光限制在薄层上所需的折射率增加。先进的波导结构，这些层的蚀刻和再生长的基础上，将制造出最佳的激光性能，并允许高功率二极管激光器泵浦。集成的开关元件将基于可饱和吸收体，其对于高强度短光脉冲具有低损耗，对于低强度连续波光具有高损耗。这些吸收器的开关特性的优化及其与波导激光器的集成将形成这项工作的主要部分。我们还将研究在简单的薄膜波导中使用克尔效应来实现短光脉冲的产生，通过使用激光谐振腔设计，利用短光脉冲的高强度将修改折射率的事实，从而实现聚焦效果。最后，已经开发了一些设备，我们将在一个很好的位置，将它们应用于生物细胞的非线性显微镜，并证明脉冲的高重复率提供的优势，在生产高光学信号，而不会造成损害的标本研究。

In this work we will develop very compact and efficient laser sources with a footprint of just a few square centimetres that are capable of producing more than a billion pulses of light per second, each having a duration of less than one tenth of one trillionth of a second. Such sources have a wide range of applications, including microscopy of biological cells, precise measurement of optical frequencies, spectroscopy and telecommunications, which can all take advantage of both the very short duration of the pulse and its high repetition rate. Many of these applications currently rely on large and relatively inefficient lasers which necessarily limits application design. The miniaturised sources that we propose are based on a waveguide geometry that confines the laser light to very small dimensions, in a similar fashion to that used in glass optical fibres. However, these waveguides are based in crystals such as titanium-doped sapphire and ytterbium-doped tungstate, which have proven themselves capable of providing the very short pulses of light that we are interested in. The waveguide geometry is also capable of supporting components that are integrated into one monolithic device that can both act as the laser gain material necessary to generate the light and provide the ultrafast switching that is required to give short pulses. The waveguides will be fabricated by growing thin layers of doped crystal on undoped substrates, with the dopant providing both the laser gain and the refractive index increase necessary to confine the light to the thin layer. Advanced waveguide structures, based on etching of these layers and re-growth, will be fabricated to give optimum laser performance and allow pumping by high-power diode lasers. The integrated switching components will be based on saturable absorbers that give low loss for high-intensity short optical pulses and high loss for low-intensity continuous wave light. Optimisation of the switching properties of these absorbers and their integration with the waveguide laser will form a major part of this work. We will also investigate the use of the Kerr effect in simple thin-film waveguides to achieve short optical pulse production by using laser resonator designs that take advantage of the fact that the high intensity of the short optical pulses will modify the refractive index such that a focussing effect is achieved. Finally, having developed a number of devices, we will be in a good position to apply them to nonlinear microscopy of biological cells and demonstrate that the high repetition rate of the pulses provides advantages in terms of producing high optical signals without causing damage to the specimens under study.