Cladding-pumped fibre Raman lasers and amplifiers

我们提出了一个为期三年的研究项目，研究包层泵浦光纤拉曼激光器和放大器在高功率光的产生和放大。我们将研究基本原理，为进一步研究这类新型器件奠定基础，并展示性能大大提高的新型激光器和放大器。我们将研究并演示高能脉冲的产生、单向脉冲放大和高增益脉冲放大。此外，在连续波（非脉冲）状态下，我们将展示一个极大扩展的波长覆盖范围，并研究连续波激光器的功率缩放到非常高的功率（bbb10kw）的潜力。这些激光器和放大器都是衍射受限的，这意味着理论上它们可以聚焦到尽可能小的一个点上。成功的关键是开发和制造满足新的和具有挑战性要求的光纤。近年来，高功率光纤激光器（包括放大器）已经取得了显著的快速进展。它们代表了一种可用于实际应用的可制造技术，并且正在成为具有重大科学和经济意义的几个应用领域的激光选择。到目前为止，这些激光器都是基于稀土掺杂光纤的包层泵浦。稀土元素的掺杂被用来在光纤中产生光学增益。包层泵送需要使用特殊的纤维设计（所谓的双包层纤维）。这使得使用多模二极管激发（泵浦）光纤激光器成为可能。多模二极管在高功率下是可用的，因此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和对光束时空参数的良好控制，从而实现对衍射受限光束的良好控制。这些因素大大降低了能源消耗，并扩大了重要材料加工应用的范围。然而，尽管取得了令人印象深刻的进展，但目前基于稀土掺杂的高功率光纤激光器和放大器的方法存在局限性，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和非常有趣的性能的新器件。他们有望克服当前高功率光纤激光技术的重要限制，并大大扩大其覆盖范围。代替稀土掺杂，受激拉曼散射被用来产生光学增益。这是发生在所有光纤中的非线性散射过程。光纤拉曼激光器的一个重要优点是，高功率稀土掺杂光纤激光器只能在特定波段工作，而光纤拉曼激光器可以在任何波长工作，这取决于泵浦波长和光纤的拉曼光谱，只受其透明度范围的限制。另一个优点是低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，这在高功率下是非常重要的。由于这将是对包层泵浦光纤拉曼激光器的第一次重要研究，计划中的研究是基础性的和探索性的，而不是详尽的。模型开发和改进理解是重要的目标。然而，我们看到包层泵浦光纤拉曼激光器的大量机会。我们完全期望在未来的许多年里，它们将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.