Coherent Raman beat analysis of the hyperfine sublevel coherence properties of 167Er3+ ions doped in an Y2SiO5 crystal

In this paper, we describe the use of coherent Raman beat (CRB) spectroscopy designed to reveal the phase coherence time t2 of the ground state hyperfine sublevels of 167Er3+ ions doped in an Y2SiO5 crystal cooled to a cryogenic temperature. The short optical coherence time T2 (~1 μs) and sublevel population lifetime t1 (~0.1 s) of the dopant Er3+ ions make it difficult to implement Raman echoes and optically detected spin echoes for measuring t2, respectively. In contrast, CRB is insensitive to the T2 and t1 values and worth employing if we can cope with inhomogeneous dephasing. By comparing carefully with the effects of sublevel inhomogeneous broadening Δ12 on the various Raman signals, we can estimate the t2 value even when t2>1/Δ12. The ground-state t2 values of the Λ-type three-level system identified in the 167Er3+ ions are approximately 12 and 50 μs when the dopant concentrations are 0.005 and 0.001 at%, respectively. These t2 values are long enough to realize electromagnetically induced transparency and coherent population trapping with an Er3+:Y2SiO5 crystal at a wavelength of 1.5 μm.