Optical hole burning is used to study optical dephasing of the 7F0 ⇒ 5D0 transition in samples of Y2O3:Eu3+ grown by both flame fusion and laser-heated pedestal growth. The samples exhibited a wide variation in their low-temperature hole widths, and the measured hole linewidths were in reasonable agreement with homogeneous linewidths obtained from values of T2 that were determined with two-pulse photon echoes. The sample that had the longest value of T2 (510 μs) from the echo measurements gave a hole width of 3.5 kHz. This is believed to be the narrowest spectral feature observed directly in the frequency domain for a solid. Other samples produced wider holes that were not correlated with the Eu3+ impurity concentrations. Time-resolved hole burning in one of the samples showed a slow and continuous broadening of the spectral hole from 130 kHz at 3 ms to 900 kHz at 10 s after hole burning. It is suggested that the additional broadening is associated with some form of disorder modes in this ordered crystalline solid.
Optical hole burning is used to study optical dephasing of the 7F0 ⇒ 5D0 transition in samples of Y2O3:Eu3+ grown by both flame fusion and laser-heated pedestal growth. The samples exhibited a wide variation in their low-temperature hole widths, and the measured hole linewidths were in reasonable agreement with homogeneous linewidths obtained from values of T2 that were determined with two-pulse photon echoes. The sample that had the longest value of T2 (510 μs) from the echo measurements gave a hole width of 3.5 kHz. This is believed to be the narrowest spectral feature observed directly in the frequency domain for a solid. Other samples produced wider holes that were not correlated with the Eu3+ impurity concentrations. Time-resolved hole burning in one of the samples showed a slow and continuous broadening of the spectral hole from 130 kHz at 3 ms to 900 kHz at 10 s after hole burning. It is suggested that the additional broadening is associated with some form of disorder modes in this ordered crystalline solid.
Two-pulse photon-echo measurements were made on the 7F0${\mathrm{\ensuremath{\leftrightarrows}}}^{5}$D0 optical transition in a number of crystalline samples of Y2O3:Eu3+ prepared by three different crystal-growth techniques. For crystals prepared by a laser-heated pedestal growth or arc-imaging furnace process, we report the observation of an additional sample-dependent contribution to the optical dephasing in comparison with a crystal grown by flame fusion. The dephasing rate 1/Tm at 1.4 K is up to two orders of magnitude faster than that previously reported for the flame-fusion-grown crystal, and is uncorrelated with concentration. Measurements up to 14 K show that 1/Tm increases linearly with temperature, in contrast to the expected T7 behavior due to a two-phonon Raman process. The linear temperature dependence is similar to that seen in glasses and disordered crystalline systems, suggesting the presence of disorder in the samples with more rapid dephasing. The crystals were examined by x-ray diffraction, excitation spectroscopy, and near-field optical microscopy to provide information on the nature of the disorder. The effect of annealing on the crystal dynamics is also investigated.
Linear- and nonlinear-optical properties of Eu3+:Y2SiO5 have been investigated. All the energy levels of the7F0,1,2,… ground-state manifold and the 5D0,1,2 excited-state manifold were identified, and they were found to be doubly structured because of the two inequivalent optical sites. Two absorption lines of the 7F0–5D0 transition were studied in detail by using nonlinear spectroscopic techniques, photon-echo and stimulated-photon-echo methods. It was found by the photon-echo measurement that the optical dephasing time for one site is extremely long and is excitation-intensity dependent. With the smallest possible intensity we observed the longest ever dephasing time in a solid, 822 μs, or a 387-Hz homogeneous linewidth. From the stimulated-photon-echo measurement, the linewidth was found to be constant over a wide range of time scales, implying the absence of spectral diffusion in this crystal. These quite advantageous properties of this crystal were used for the demonstration of two novel types of time-domain optical data readout: time- and frequency-domain hybrid optical memory and spectrally programmed coherent transients.
Laser induced hole burning in optical absorption bands of low temperature solids has been investigated with emphasis on mechanisms for population hole burning, the interactions with the environment which limit the hole widths and the use of hole burning for ultra high resolution spectroscopy. Hole burning was observed in a wide range of solids including organic and organometallic molecules in crystals and rare earth ions in crystals and glasses. The mechanisms for hole burning also varied widely and a new mechanism involving optically induced nuclear spin flips of near neighbor nuclei was discovered. Examples of hole burning in new classes of materials are presented here for the first time, namely inorganic glasses (silicate glasses containing Nd(3+), Pr(3+) or Eu(3+)) and undoped stoichiometric compounds (e.g., EuP5O14). Hole recovery was used to determine nuclear spin lattice relaxation rates in praseodymium doped crystals. For allowed optical transitions (e.g., singlet states of zinc porphyrin, dibromoindigo and color centers in alkali halides) the hole widths at 2K are limited by population decay to approximately 50 MHz. For longer lived optical levels in crystalline materials, e.g., those containing rare earth ions, the hole widths are narrower (less than 10 MHz) and are limited by dynamical interactions with surrounding nuclei. In amorphous materials such as europium doped silicate glass, hole widths are much broader, being limited by low frequency tunneling motions. Hole burning measurements were complemented by time domain coherent transient (photon echo, and optical free decay) measurements of homogeneous linewidths which enabled us to measure optical resonances as narrow as 760 Hz in Eu(3+):Y2O3.
Optical dephasing in a number of crystalline samples of Y 2 O 3 : Eu 3+ prepared by two different crystal-growth techniques were measured using two pulse photon echo method. For crystals prepared by a laser-heated pedestal growth, we report the dephasing rate, 1/ T m , at 1.4 K is up to two orders of magnitude faster than that previuosly reported for the flame fusion growth crystal. The spatial dependence of the optical dephasing rate, measured by TPPE (two-pulse photon echo), tells that the environments of echo producing ions at least highly depend on the spatial position which can not be detected by conventional laser spectroscopy techniques, suggesting two-pulse photon echo experiment can be served as a tool for probing the uniformity of the samples.
We report a spectroscopic study of the 7F0–5D1 transition of europium ions in crystal yttrium orthosilicate (Eu3+:Y2SiO5) with a focus on low-temperature properties relevant to its use in time-domain optical data storage. The optical dephasing time T2 for this green transition was found to be approximately 50 μs for Eu3+ in one optical site (site 1) and 56 μs for Eu3+ in the other site (site 2), both of which exceeded their respective excited-state lifetimes (32 μs for site 1 and 42 μs for site 2). Of the two optical sites, the transition on site 2 has a slightly larger inhomogeneous linewidth (~2.7 GHz) but a significantly larger oscillator strength (~6 × 10−8), making it a good candidate for time-domain optical storage. The hyperfine structures of the transition for both sites were also measured by spectral hole burning.
The optical spectroscopy and dynamics of three materials; Eu^3+:Y2SiO5, Pr^3+:Y2SiO5, and Tm^3+:Y2SiO5 that are of interest for application in persistent spectral holeburning optical memory and signal processing devices were investigated using linear and nonlinear spectroscopic techniques.Two-pulse photon echoes have been used to measure the homogeneous linewidths.The effects of instantaneous spectral diffusion were systematically studied to allow accurate determination of the optical resonance widths, and external magnetic fields were applied to characterize the effects of fluctuating nuclear spins of the host lattice on dephasing of the dopant ion.The 7F0 → 5D0 transition of 0.1% Eu^3+ in the two crystallographic sites of Y2SiO5 was studied using photon echoes.Using this material, we succeeded in measuring the narrowest optical resonance in a solid by shielding the crystal from stray electromagnetic fields and using sufficiently low laser power to minimize contributions from instantaneous diffusion.The homogeneous linewidths measured in a magnetic field of 100 G are 122 Hz (site 1) and 167 Hz (site 2).These widths are dominated by population decay, but up to 20 Hz is attributed to 89Y spin fluctuations which have been reduced by the applied magnetic field.Similar studies were performed to determine the contributions to the homogeneous linewidth of the 3H4(1) → 1D2(1) transition for both sites of 0.02% Pr^3+ in Y2SiO5.Linewidths of 2.1 kHz (site 1) and 0.85 kHz (site 2) were obtained with an applied magnetic field of 77 G.A significant contribution of 89Y nuclear spin fluctuations to the zero-field homogeneous linewidth was found.Optically detected nuclear magnetic resonance measurements determined the hyperfine structure of the 3H4 ground state for each site, and photon echo nuclear double resonance was used to determine the hyperfine levels of the lowest component of the 1D2 manifold. 3) 2.1? Ec,2S