Cladding-pumped fibre Raman lasers and amplifiers

我们提出了一个为期三年的研究计划，调查包层泵浦光纤拉曼激光器和放大器的产生和放大的光在高功率。我们将研究基本原理，为进一步研究这类新器件奠定基础，并展示性能大大改善的新激光器和放大器。我们将研究和演示高能量脉冲的产生，单向脉冲放大，以及具有非常高增益的脉冲放大。此外，在连续波（非脉冲）制度，我们将展示一个大大扩展的波长覆盖范围，以及调查的潜力，连续波激光器的功率缩放到非常高的功率（> 10千瓦）。这些激光器和放大器都是衍射限制的，这意味着它们可以被聚焦到理论上可能的最小光斑。成功的关键是开发和制造满足新的和具有挑战性的要求的光纤。近年来，高功率光纤激光器（包括放大器）的发展非常迅速。它们代表了现实世界应用的可制造技术，并正在成为具有重要科学和经济意义的几个应用领域的首选激光器。迄今为止，这些激光器是基于稀土掺杂光纤的包层泵浦。掺杂稀土元素用于在光纤中产生光学增益。包层泵浦需要使用特殊的光纤设计（所谓的双包层光纤）。这使得能够使用多模二极管来激励（泵浦）光纤激光器。多模二极管在高功率下可用，使得由它们泵浦的光纤激光器也可以达到高功率。高功率光纤激光器的重要优点包括高效率以及对时间和空间光束参数的出色控制，从而可以实现良好控制的衍射限制光束。这些因素显著降低了能源消耗，并扩大了重要材料加工应用的范围。尽管取得了令人印象深刻的进展，但目前基于掺杂稀土的高功率光纤激光器和放大器的方法具有限制，阻碍了当前和未来的进展。包层泵浦光纤拉曼激光器和放大器构成了一类具有独特且非常有趣的特性的新器件。它们有望克服当前高功率光纤激光器技术的重要限制，并大大扩展其应用范围。代替稀土掺杂，受激拉曼散射用于产生光学增益。这是一种非线性散射过程，发生在所有光纤中。光纤拉曼激光器的一个重要优点是，虽然高功率稀土掺杂光纤激光器仅在某些波段工作，但光纤拉曼激光器可以在任何波长下工作，该波长由光纤的泵浦波长和拉曼光谱确定，并且仅受其透明度范围的限制。另一个优点是低的热负荷和潜在的更长的相互作用长度。这些因素都减少了热效应的影响，这是非常重要的，在高powers.Since这将是第一次有意义的研究包层泵浦光纤拉曼激光器，计划的调查是基本的和探索性的，而不是详尽无遗的。模型开发和提高认识是重要的目标。然而，我们看到了大量的机会与包层泵浦光纤拉曼激光器。我们完全期待它们在未来的许多年里成为进一步深入研究的主题，并且光纤激光器将继续扩展到新的实际应用中。

We propose a three year long research project to investigate cladding-pumped fibre Raman lasers and amplifiers for the generation and amplification of light at high powers. We would study the fundamentals and lay a basis for further studies of this new class of devices as well as demonstrate new lasers and amplifiers with greatly improved properties. We would investigate and demonstrate the generation of high-energy pulses, unidirectional pulse amplification, and pulse amplification with very high gain. Furthermore, in the continuous-wave (non-pulsed) regime, we would demonstrate a greatly extended wavelength coverage as well as investigate the potential of power scaling of continuous-wave lasers to very high powers (> 10 kW). These lasers and amplifiers would all be diffraction-limited, which means that they can be focussed to as small a spot as theoretically possible. Key to success would be to develop and fabricate optical fibres that meet new and challenging requirements. High-power fibre lasers (including amplifiers) have already seen a remarkably rapid progress in recent years. They represent a manufacturable technology for real-world applications, and are becoming the laser of choice in several application areas of great scientific and economic importance. To date, these lasers are based on cladding-pumping of rare-earth doped fibres. Doping with rare-earth elements is used to create optical gain in the fibres. Cladding-pumping requires the use of special fibre designs (so-called double-clad fibres). These enable the use of multimode diodes to energise ( pump ) the fibre lasers. Multimode diodes are available at high powers, so that also the fibre lasers pumped by them can reach high powers. Important advantages of high-power fibre lasers include high efficiency and excellent control of temporal and spatial beam parameters, so that well-controlled diffraction-limited beams can be realised. These factors significantly reduce the energy consumption and extend the reach of important materials processing applications. Still, despite the impressive progress, the current approach to high-power fibre lasers and amplifiers, based on doping with a rare earth, has limitations that hampers current and future progress.Cladding-pumped fibre Raman lasers and amplifiers constitute a new class of devices with unique and very interesting properties. They promise to overcome important limitations of current high-power fibre laser technology and greatly expand their reach. Instead of rare-earth doping, stimulated Raman scattering is used to create optical gain. This is a nonlinear scattering process that occurs in all optical fibres. One important advantage of fibre Raman lasers is that whereas high-power rare-earth doped fibre lasers only work in certain wavelength bands, fibre Raman lasers can operate at any wavelength, determined by the pump wavelength and the Raman spectrum of the fibre and limited only by its transparency range. Another advantage is a low thermal load and potentially longer interaction length. These factors both reduce the impact of thermal effects, which is very important at high powers.Since this would be the first significant study of cladding-pumped fibre Raman lasers, the planned investigations are fundamental and exploratory rather than exhaustive. Model development and improved understanding are important objectives. Nevertheless, we see a large number of opportunities with cladding-pumped fibre Raman lasers. We fully expect them to be the subject of further and deeper studies over many years to come, and that the expansion of fibre lasers into new real-world applications will continue.