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

具有窄线宽、高稳定性和连续可持续性的固体紫外激光源在原子和分子光谱学、激光冷却和量子光学应用中具有重要意义。紫外范围的标准和商用方法是使用二次谐波产生（SHG）扩展染料激光器的光谱覆盖范围，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。然而，这些方法在规模和成本方面都有局限性。高功率光纤激光技术的最新进展和准相位匹配（QPM）非线性材料的出现为开发紧凑可靠的紫外激光源开辟了新的机会。在此，我们提出通过一系列非线性光转换过程将光纤激光系统在电信范围（1.5 μm）内的辐射转换为紫外（~ 310 nm）。我们的初步研究表明，这是一种很有前途的方法，它利用了相对低成本的激光器和可用于电信光谱范围的激光组件，以及现在广泛使用的准相位匹配非线性晶体。超长的使用寿命和易于使用的远程范围激光器是一个显著的优势，因为这些特点是重要的，今天的实验变得越来越复杂。在这个项目中，我们建议在实际应用中开发一个完整的、交钥匙式的连续波紫外线源，激光冷却Be+离子。需要实现的重要规格是在自由运行模式下1小时内频率不稳定性小于50 MHz，使用分子参考的主动稳定时频率不稳定性小于1 MHz，以及输出功率为200 mW。这个系统将足够简单，其他研究小组可以以合理的成本复制/调整设计并建立类似的来源。它将在光谱学或量子光学应用中非常有用。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激光源的重要一步，这将使量子光学中的许多应用成为可能。这个扩展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.