Time-resolved transient spectral hole-burning experiments in zero field and in low magnetic fields B( parallelc) are reported for the chromium(III) R(1)-line, 2A((2)E)<-- 2A((4)A(2)) of Chatham lab created emerald, Be(3)Al(2)Si(6)O(18)ratio Cr(III)(0.0017% per weight), in the temperature range of 3 to 12 K. In low magnetic fields and temperatures >5 K conversion of side-holes to anti-holes is observed with progressing time. Anti-holes are due to the population stored in ground state levels. The dynamics of the hole pattern can be well modelled by a set of coupled differential equations for the levels of the (4)A(2) and (2)E multiplets. The measurements allow the simultaneous determination of g-factors and spin-lattice relaxation rates in the excited state and the ground state. At 6 K the relaxation times between the split +/-1/2 2A((2)E) excited state levels and +/-3/2 2A((4)A(2)) levels of the ground state are about 0.16 ms and 9 ms, respectively. From the temperature dependence it follows that the spin-lattice relaxation rates are dominated by Orbach processes in the experimental temperature range.
We report on the observation of slow light induced by transient spectral hole-burning in a solid, that is based on excited-state population storage. Experiments were conducted in the R1-line (2E←4A2 transition) of a 2.3 mm thick pink ruby (Al2O3:Cr(III) 130 ppm). Importantly, the pulse delay can be controlled by the application of a low external magnetic field B||c≤9 mT and delays of up to 11 ns with minimal pulse distortion are observed for ~55 ns Gaussian pulses. The delay corresponds to a group velocity value of ~c/1400. The experiment is very well modelled by linear spectral filter theory and the results indicate the possibility of using transient hole-burning based slow light experiments as a spectroscopic technique.
The temperature dependence of transient and persistent spectral holes is reported for the R-lines ( 2 E ← 4 A 2 transitions) in 4% chromium(III) doped NaMgAl(oxalate) 3 ·9H 2 O. The temperature dependence is well described by taking into account two pseudolocal vibrations in a weak electron−phonon coupling model and the direct process between the two 2 E levels. The persistent spectral hole-burning is based on a non photochemical mechanism involving mainly a rearrangement of a water molecule of crystallization. The 1.12 GHz width of the transient hole in the R 2 line provides a value for the relaxation rate within the 2 E multiplet, k (R 2 → R 1 ) = 3.5 × 10 9 s -1 at 2.5 K. The observed optical line width of Γ = 46 MHz for the R 1 -line at 2.5 K is most likely dominated by chromium(III)−chromium(III) spin−spin interactions. Spectral diffusion on the ms time scale causes persistent spectral holes to be significantly broader and holewidths of 260 MHz and 1.63 GHz for the R 1 and R 2 -line, respectively, are observed. Spontaneous hole-filling is thermally activated and spectral diffusion on the minute time scale is slow in the investigated temperature range of 2.5−30 K.
Spectral hole burning on the $4{f}^{7}(^{8}S_{\frac{7}{2}})\ensuremath{\rightarrow}4{f}^{6}5d$ transition of
Eu2+ is observed to occur by two mechanisms in Ca
F2:
Eu2+. At zero magnetic field, persistent spectral hole burning occurs by two-step photoionization where the hole burning survives cycling to room temperature. The observed hole spectrum is compared with a calculation which considers the small
Eu2+ ground-state splitting and both the ground- and excited-state hyperfine interactions. In a magnetic field above 1 T, transient spectral hole burning occurs by population redistribution among the ground-state hyperfine levels. Long-lived (minutes) holes are observed for a half integral spin system. The resulting hole spectrum consists of holes, antiholes, and a nuclear spin-flip sideband and can be explained from the hyperfine interactions in the ground and excited states. The dominant hole decay occurs by phonon-induced transitions among hyperfine levels of the ${M}_{S}=\ensuremath{-}\frac{7}{2}$ and ${M}_{S}=\ensuremath{-}\frac{5}{2}$ electron-spin sublevels. Central hole linewidths of 200 MHz are observed at zero magnetic field. Hole linewidths at high magnetic fields are as narrow as 40 MHz but these are inhomogenously broadened by superhyperfine interactions with the
F nuclear spins. Estimates of hole-burning quantum efficiency are also obtained.
Slow light based on transient spectral hole-burning is reported for emerald, Be(3)Al(2)Si(6)O(18):Cr(3+). Experiments were conducted in π polarization on the R(1)(± 3/2) line (E2 ← A(2)4) at 2.2 K in zero field and low magnetic fields B||c. The hole width was strongly dependent on B||c, and this allowed us to smoothly tune the pulse delay from 40 to 154 ns between zero field and B||c = 15.2 mT. The latter corresponds to a group velocity of 16 km/s. Slow light in conjunction with a linear filter theory can be used as a powerful and accurate technique in time-resolved spectroscopy, e.g., to determine spectral hole-widths as a function of time.
Persistent and time-resolved transient holes were burnt into the
1D2${\ensuremath{\leftarrow}}^{3}$
H4 transition of
Pr3+ and the
5D0${\ensuremath{\leftarrow}}^{7}$
F0 transition of
Eu3+ in silicate glasses. The holewidths were studied as a function of burning-fluence density, wavelength, and temperature between 0.4 and 12 K. Transient holes arising from optical pumping of ground-state nuclear hyperfine levels were found for both ions at T3 K. Their lifetime decreases with increasing temperature. They are accompanied by symmetrically placed antiholes. For
Eu3+, two pairs of antiholes were found which are attributed to the two europium isotopes,
151Eu and
153Eu. For
Pr3+, an additional mechanism leading to persistent hole burning dominates above 3 K. The holewidth follows a ${\mathit{T}}^{(1.3\ifmmode\pm\else\textpm\fi{}0.1)}$ dependence for
Pr3+ and a ${\mathit{T}}^{(1.0\ifmmode\pm\else\textpm\fi{}0.1)}$ dependence for
Eu3+. The temperature dependence is the same as that of the contribution of the two-level systems to the specific heat measured on the same samples and in the same temperature range. The quadrupole splittings of the
7F0 ground state and the crystal-field splittings of the
7F1 and
7F2 levels of
Eu3+ as a function of excitation wavelength indicate that the strength of the noncubic component of the crystal field varies monotonically for excitation across the
5D0${\ensuremath{\leftarrow}}^{7}$
F0 absorption band, falling to zero at the long-wavelength edge. The hole width shows a similar variation with excitation frequency. No influence of the experimental time scale on the hole width was detected for either sample between ${10}^{\mathrm{\ensuremath{-}}2}$ and
102 s.