Subnanometer optical linewidth of thulium atoms in rare-gas crystals

We investigate the 1140 nm magnetic-dipole transition of thulium atoms trapped in solid argon and neon. These solids can be straightforwardly grown on any substrate at cryogenic temperatures, making them prime targets for surface-sensing applications. Our data are well described by a splitting of the single vacuum transition into three components in both argon and neon, with each component narrower than the 0.8 nm spectrometer resolution. The lifetime of the excited states is 14.6(0.5) ms in argon and 27(3) ms in neon, shorter than in vacuum or in solid helium. We also collected visible laser-induced fluorescence spectroscopy showing broader emission features in the range of 580–600 nm. The narrow infrared features in particular suggest a range of possible applications.

Figure 1

Experimental setup for trapping thulium atoms in rare-gas matrices. The flow of rare gas is controlled by using the mass flow controller (MFC) and thulium atoms are obtained by ablation with a 532 nm pulsed laser (green beam).

Figure 2

Two-dimensional emission spectra of thulium in argon (left) and neon (right) at different excitation wavelengths normalized by excitation power. The top two figures are the observed fluorescence signal at excitation wavelengths 561 nm (black) and 580.6 nm (red) curves.

Figure 3

Diagram of the relevant energy levels for thulium atom in vacuum. The numbers on the transitions indicate wavelength in nm.

Figure 4

The emission spectra of the ${}^{2}F_{5/2}-{}^{2}F_{7/2}$ transition in argon (left) and in neon (right) with excitation at 594.8 nm. The solid red curves are fits to a model based on three resolution-limited Gaussian curves (full width and half maximum: 0.8 nm). Error bars indicate statistical uncertainty.

Figure 5

Excitation spectrum of thulium measured in a neon crystal from 582 to 602 nm. The monitored wavelength was 1140 nm. Error bars indicate statistical uncertainty. The excitation laser linewidth is less than 0.1 nm.

Figure 6

The decay of the ${}^{2}F_{5/2}-{}^{2}F_{7/2}$ transition of thulium in argon and neon. The solid line is obtained by fitting a curve of the form $A{e}^{-t/\tau }+B$, with the lifetime $\tau$ indicated.