Spectral hole lifetimes and spin population relaxation dynamics in neodymium-doped yttrium orthosilicate

Abstract

We present a detailed study of the lifetime of optical spectral holes due to population storage in Zeeman sublevels of Nd 3+ :Y 2 SiO 5 . The lifetime is measured as a function of magnetic field strength and orientation, temperature, and Nd 3+ doping concentration. At the lowest temperature of 3 K we find a general trend where the lifetime is short at low field strengths, then increases to a maximum lifetime at a few hundred mT, and then finally decays rapidly for high field strengths. This behavior can be modeled with a relaxation rate dominated by Nd 3+ -Nd 3+ cross relaxation at low fields and spin lattice relaxation at high magnetic fields. The maximum lifetime depends strongly on both the field strength and orientation, due to the competition between these processes and their different angular dependencies. The cross relaxation limits the maximum lifetime for concentrations as low as 30 ppm of Nd 3+ ions. By decreasing the concentration to less than 1 ppm we could completely eliminate the cross relaxation, reaching a lifetime of 3.8 s at 3 K. At higher temperatures the spectral hole lifetime is limited by the magnetic-field-independent Raman and Orbach processes. In addition we show that the cross relaxation rate can be strongly reduced by creating spectrally large holes of the order of the optical inhomogeneous broadening. Our results are important for the development and design of new rare-earth-ion doped crystals for quantum information processing and narrow-band spectral filtering for biological tissue imaging.

Efficient optical pumping using hyperfine levels in 145Nd3+:Y2SiO5 and its application to optical storage

“…As seen the lifetimes generally increase at low fields, reach a maximum around 0.4 T, and then start to decrease for higher fields, similarly to the case of ions with I=0. In [20] it was found that a SLR model including the direct, Raman and Orbach processes explained well the high-field data for ions with I=0. In figure 4 the blue solid line shows the lifetime predicted by this model, using the fitted parameters [20] for this particular magnetic field angle (D 1 axis).…”

“…Finally, we comment on the lifetimes measured below 0.5 T, where spin flip-flops limit the spectral hole lifetime for ions with I=0 [20]. We first note that for fields down to about 0.15 T, the hyperfine Hamiltonian is still a perturbation to the Zeeman Hamiltonian, in which case one would expect the spin flip-flop process to mainly drive the R 0 transition shown in figure 3.…”

“…We denote this ground state relaxation rate R 0 , as shown in figure 3. For a magnetic field of 900 mT for which the results are shown in figure 2, the dominant relaxation process is the direct spin-lattice relaxation (SLR) [20]. For the SLR process this relaxation path is expected to have the highest rate (shortest lifetime) [36], due to the low spin mixing.…”

“…To better understand the relaxation mechanisms governing the fast and slow decays, we measured the hole decay curve for fields in the range of 10 mT-1.6 T. But before discussing these results, we briefly recall the main findings of [20] where we studied the decay of spectral holes due to relaxation between m S =±1/2 states for ions with no nuclear spin I=0. At low fields (around 0.5 T) the decay was given by spin-spin relaxation, with a linear increase of the spectral hole lifetime as a function of applied magnetic field B.…”

“…Recently we presented a detailed study of the spectral hole lifetime in naturally doped Nd 3+ :Y 2 SiO 5 [20], as a function of magnetic field strength and direction, temperature (between 3 and 5.5 K) and Nd 3+ doping concentration. It was found that the spectral hole dynamics were dominated by the population relaxation between the electronic Zeeman states m S =±1/2 of even Nd 3+ isotopes having zero nuclear spin I=0.…”