Direct two-photon excitation of isomeric transition in thorium-229 nucleus

TL;DR

This paper explores the feasibility of two-photon excitation of the thorium-229 nuclear isomeric state using laser irradiation, demonstrating potential for nuclear fluorescence detection in ions and crystals.

Contribution

It introduces a method for two-photon excitation of thorium-229's isomeric state, comparing monochromatic and pulsed light, and discusses experimental conditions for maximal fluorescence.

Findings

Two-photon excitation yields identical fluorescence for monochromatic and pulsed light.

Saturation of fluorescence achievable with focused laser at 320 nm and 100 mW.

Detection of several photons per second at 160 nm in doped crystals.

Abstract

A possibility of the two-photon excitation of an isomeric state in a nucleus of thorium-229 has been discussed. The fluorescence intensity of the excitation is demonstrated to be identical for the irradiation of nuclei with either monochromatic light or polychromatic radiation consisting of a sequence of short light pulses of the same intensity. The two-photon excitation of Th^{3+} ion in an electromagnetic trap with a focused laser beam with a wavelength of about 320 nm and power of 100 mW can lead to the absorption saturation, at which the fluorescence emission with the frequency of the transition in a nucleus is maximal. In crystals doped with Th^{4+} to a concentration of about 10^{18} cm^{-3} and irradiated with a laser radiation 10 W in power, the emission of several photons per second with a wavelength of about 160 nm becomes possible.