Optical clocks based on neutral cadmium are of interest because the black‑body radiation (BBR) shift on the clock transition is an order of magnitude smaller than in strontium or ytterbium, easing thermal control and enabling higher accuracy in practical systems [1]. Cd can also be efficiently laser‑cooled: a broad transition at 228.9 nm supports rapid loading directly from vapour, and a narrow intercombination line at ~326 nm (linewidth ~66 kHz) allows μK‑level cooling for precision spectroscopy [2]. Further, the 1 S0- 3P0 clock transition near 332 nm is an attractive platform for precision metrology and single‑photon interferometry.
Aim: In this project we will design, build, and apply ultra‑low‑noise UV laser systems tailored to Cd cooling and precision spectroscopy, in close collaboration with Dr Stefan Truppe’s group (Imperial College London [3]) and with Fraunhofer CAP for translation towards deployable sources.
Context and novelty: Deep‑UV laser sources, particular when high coherence is required, are very challenging and currently confined to large lab-based systems. However, following our recent work on compact, high power, ultra-narrow-linewidth red (689 nm) lasers for Sr (see e.g. [4]) we now have the opportunity to explore low noise intra-cavity nonlinear harmonic generation of the
wavelengths required for Cd, within lasers immune to so-called nonlinear ‘green noise’ and with sub-Hz intrinsic linewidth. In an early result, we previously demonstrated narrow linewidths at 338 nm via intra-cavity second harmonic generation [5]. In parallel, our collaborators have recently established deep‑UV laser‑cooling platforms for atoms and molecules, providing a unique experimental testbed and know‑how in DUV optics [3, 6, 7]. Building on that platform, this project will target ultra‑stable UV outputs at 326 nm and 332 nm with sub‑kHz linewidths, leveraging techniques such as intracavity doubling (e.g. 664 → 332 nm) and vibration‑insensitive cavities with active frequency noise suppression. The UV sources will be engineered for low frequency noise, high passive stability, and robust DUV optics handling.
Technical objectives:
• 326 nm narrow‑line cooling laser with intensity/frequency noise below the natural linewidth of the Cd transition to enable μK cooling and high‑SNR spectroscopy of Cd.
• 332 nm clock‑spectroscopy laser (via intracavity SHG) targeting sub‑kHz linewidth and long‑term stability compatible with coherent interrogation, with an enhancement cavity contingency if required.
• Noise metrology and dynamics: characterise intensity, frequency and phase noise; model/measure nonlinear conversion dynamics and UV‑induced degradation pathways.
• Application experiments (with Imperial): perform narrow‑line cooling at 326 nm, then spectroscopy on/near the 332 nm clock transition.
Expected outcomes:
• Demonstration of compact, low‑noise 326 nm and 332 nm UV sources suitable for
advanced Cd spectroscopy.
• Narrow‑line cooling and clock‑transition spectroscopy in Cd.
• Peer‑reviewed publications in laser design, UV nonlinear optics, and precision
spectroscopy; technology path towards compact optical clocks for PNT applications