A laser excitation scheme for $^{229\text{m}}$Th

TL;DR

This paper proposes a practical laser excitation method for the $^{229}$Th nuclear isomer that leverages existing laser technology and internal conversion detection, enabling nuclear laser spectroscopy without needing extremely precise energy knowledge.

Contribution

It introduces a novel excitation scheme for $^{229}$Th that bypasses the need for highly precise isomer energy measurements, using internal conversion for detection.

Findings

Achieves a signal-to-background ratio >10^4

Allows nuclear laser spectroscopy with existing lasers

Requires less than three days for laser scanning

Abstract

Direct laser excitation of the lowest known nuclear excited state in $^{229}$Th has been a longstanding objective. It is generally assumed that reaching this goal would require a considerably reduced uncertainty of the isomer's excitation energy compared to the presently adopted value of $(7.8\pm 0.5)$ eV. Here we present a direct laser excitation scheme for $^{229\text{m}}$Th, which circumvents this requirement. The proposed excitation scheme makes use of already existing laser technology and therefore paves the way for nuclear laser spectroscopy. In this concept, the recently experimentally observed internal-conversion decay channel of the isomeric state is used for probing the isomeric population. A signal-to-background ratio of better than $10^4$ and a total measurement time of less than three days for laser scanning appear to be achievable.