Formation and optical properties of laser-active N2 centers in KCl.

Abstract

Recent experimental results on the formation and optical properties of the laser-active ${\mathit{N}}_{2}$ center in additively colored pure KCl are reported. The ${\mathit{N}}_{2}$ center in KCl is most efficiently formed through a photoaggregation process in heavily colored crystals exposed to light on the long-wavelength shoulder of the F band. The observed room-temperature stability of the ${\mathit{N}}_{2}$ center indicates that it is an electrically neutral defect. Absorption and emission bands peak at 1.02 and 1.25 \ensuremath{\mu}m, respectively. The ${\mathit{N}}_{2}$-band absorbance grows proportionally with the ${\mathit{R}}_{1}$- and ${\mathit{R}}_{2}$-band absorbances. Polarized ${\mathit{N}}_{2}$-center fluorescence data is consistent with two degenerate orthogonal dipole moments lying on {111} planes of the crystal. Excited-state absorption spectra show higher transitions coincident in wavelength with the ${\mathit{R}}_{1}$ and ${\mathit{R}}_{2}$ absorption bands of the trigonal ${\mathit{F}}_{3}$ color center in KCl. Similar experiments on the ${\mathit{R}}_{1}$ band correlate well with the ${\mathit{N}}_{2}$-center data. Results are consistent with the identification of the laser-active part of the ${\mathit{N}}_{2}$ band as a transition of the trigonal ${\mathit{F}}_{3}$ color center.