Development of tunable continuous-wave UV laser source of high spectral purity and demonstration of high-resolution spectroscopy

具有窄线宽、高稳定性和连续可伸缩性的固态紫外光光源在原子分子光谱学、激光制冷和量子光学应用中具有重要意义。使用二次谐波产生(SHG)、单个激光器的级联频率转换(SHG+SHG)或一对激光器的级联SHG+和频率产生(SHG+SFG)技术来扩展染料激光器的光谱覆盖范围是标准的和商业上可用的方法。然而，这些方法在体积和成本方面都有局限性。最近高功率光纤激光器技术的进步和准相位匹配(QPM)非线性材料的出现为紧凑型和可靠的UV激光光源的发展提供了新的机遇。本文提出通过级联的非线性光学转换过程，将光纤激光系统在电信范围内(1.5μm)的辐射转换成紫外光(~310 nm)。我们的初步研究表明，这是一种很有前途的方法，它利用了可用于电信光谱范围的相对低成本的激光和激光元件，以及现在广泛使用的准相位匹配非线性晶体。电信距离激光器的超长寿命和易用性是一个显著的优势，因为这些特性对于今天日益复杂的实验非常重要。在这个项目中，我们建议开发并表征一个完整的、交钥匙类型的连续紫外光光源，在实际应用中，激光冷却Be+离子。要达到的重要指标是在自由运行模式下频率不稳定在1小时内小于50 MHz，使用分子基准的有源稳定时频率不稳定小于1 MHz，以及200 mW的输出功率。该系统将足够简单，其他研究小组可以复制/修改设计并以合理的成本建造类似的源。这项工作的成功完成也将是迈向用于Be+离子拉曼边带冷却的紫外光光源的关键一步，使其在量子光学中的一些应用成为可能。这一延期将是未来提案的主题。

Solid-state UV laser sources with narrow linewidth, high stability and continuous tenability are important for atomic and molecular spectroscopy, laser cooling, and quantum optics applications. The standard and commercially available approach to the UV range is extension of spectral coverage of dye lasers using second harmonic generation (SHG), cascaded frequency conversion (SHG + SHG) of a single laser or cascaded SHG + sum frequency generation (SHG+SFG) techniques of a pair of lasers. These approaches have, however, limitations in terms of size and cost.Recent advances in high power fiber laser technology and the advent of quasi-phasematched (QPM) nonlinear materials open new opportunities for the development of compact and reliable UV laser sources. We propose here to convert the radiation from a fiber laser system in the telecom range (1.5 μm) to the UV (~ 310 nm) by a cascade of nonlinear-optical conversion processes. Our initial investigations have shown that this is a promising approach, which makes use of the relatively low-cost laser and laser components available for the telecom spectral range, and the now widely available quasi-phasematched nonlinear crystals. The exceptionally long lifetime and ease of use of the telecom-range laser is a significant advantage since these features are of importance for today’s experiments that are becoming increasingly complex.In this project we propose to develop and then characterize a complete, turnkey-type cw UV source in a real application, laser cooling of Be+ ions. Important specifications to be achieved are a frequency instability of less than 50 MHz over 1 h in free-running mode and less than 1 MHz using active stabilization to the molecular reference, as well as an output power of 200 mW.This system will be sufficiently simple that other research groups may copy/adapt the design and build similar sources, at a reasonable cost. It will be useful for spectroscopic or quantum optical applications.The successful completion of this work will also be the essential step toward a UV laser source for Raman sideband cooling of Be+ ions, with which a number of applications in quantum optics become possible. This extension will be the subject of a future proposal.