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.
Systematic measurements of stimulated-photon-echo intensities as a function of the first-to-second (\ensuremath{\tau}) and second-to-third (T) pulse separations allow the investigation of the dynamical properties of the spectral diffusion for the
7F0${\mathrm{\ensuremath{-}}}^{5}$
D0 transition of a cryogenic
Eu3+:
YAlO3 sample. The existence of spectral diffusion was verified by the significant broadening (from 1.2 to 7.2 kHz) of the homogeneous linewidth (\ensuremath{\Gamma}) as T increases from microseconds to milliseconds, the effect being attributed to the flip flop of nearby aluminum nuclear spins surrounding the
Eu3+ ion. A similar broadening effect (from 0.61 kHz, to a few kHz) was also observed in the presence of a static magnetic field
H0=137 G, but with a much slower diffusion rate. To explain these observations, we use three theoretical models: the Bai-Fayer model, the diffusion-equation model, and the Monte Carlo model. Each agrees reasonably well with the experimental data and indicates the flip rates of sub-kHz order at
H0=0 and an order of magnitude lower at 137 G.
We report ultraslow group velocities of light in a solid. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 microsecond(s) in a 3-mm thick, optically dense crystal of Pr doped Y2SiO5. Reduction of the group velocity is accomplished by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence. Potential applications of slow and stopped light for the highly efficient storage and recall of optical data are discussed.
The $^{2}F_{7/2}\ensuremath{\leftrightarrow}^{2}F_{5/2}$ optical transitions of
Yb3+ doped into
Y3Al5O12 (YAG) were studied for potential quantum information and photonic signal processing applications. Absorption and fluorescence spectroscopy located the energy levels of the ground
2F7/2 and excited
2F5/2 manifolds, allowing inconsistencies between previous assignments of crystal field splittings in the literature to be resolved. These measurements reveal an unusually large splitting between the first and second levels in both the ground and excited multiplets, potentially providing for reduced sensitivity to thermally induced decoherence and spin-lattice relaxation. Spectral hole burning through two-level saturation was observed, determining the excited state lifetime to be 860 \ensuremath{\mu}s and resolving ambiguities in previous fluorescence measurements that were caused by the large radiation trapping effects in this material. Optical decoherence measurements using two-pulse photon echoes gave a homogeneous linewidth of 18 kHz for an applied magnetic field of 1 T, narrowing to 5 kHz at 2.5 T. The observed decoherence was described by spectral diffusion attributed to $\mathrm{Y}{\mathrm{b}}^{3+}\mathrm{\ensuremath{-}}\mathrm{Y}{\mathrm{b}}^{3+}$ magnetic dipole interactions. Laser absorption determined an inhomogeneous linewidth of 3.6 GHz for this transition in this 0.05%-doped crystal, which is narrower than for any other rare-earth-ion transition previously studied in the YAG host. The temperature dependence of the transition energy and linewidth of the lowest
2F7/2 to lowest
2F5/2 transition centered at 968.571 nm measured from 4 K to 300 K was well described by phonon scattering at higher temperatures, with an additional anomalous linear temperature-dependent broadening at temperatures below 80 K. Two magnetically inequivalent subgroups of
Yb3+ ions were identified when a magnetic field was applied along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axis, as expected for the
D2 sites in the cubic symmetry crystal, with ground and excited state effective
g-values of
gg=3.40 (3.34) and
ge=1.04 (2.01), respectively. Together with the convenient diode laser wavelength of this transition, our study suggests that
Yb3+:YAG is a promising material system for spectral hole burning and quantum information applications.
Two-photon persistent hole burning is observed at T = 296 K in 5 D 1 – 7 F 0 and 5 D 0 – 7 F 0 transitions of Sm 2+ ions in substitutionally disordered SrFCl 1/2 single crystals, showing the ratio of inhomogeneous to homogeneous linewidth of 20 ÷ 25. The minimum hole widths of 3.5 cm -1 and 2.6 cm -1 , respectively, were determined for these transitions. In fact, the applicability of persistent spectral hole burning, known as a low-temperature high-resolution spectroscopic method and a potential basis for the use of a new–spectral–dimension in optical data storage and processing, is demonstrated for the first time at room temperature in inorganic materials.