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

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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.