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Physical Review B

Optical decoherence and energy level structure of 0.1 % Tm 3+ :LiNbO 3

Yiwen Sun, Charles W. Thiel, R. L. Cone

Published Apr 6, 2012• 43 citations
Publisher

Abstract

We report the energy level structure of the ${}^{3}$H${}_{6}$ and ${}^{3}$H${}_{4}$ multiplets for Tm${}^{3+}$ doped congruent LiNbO${}_{3}$, as well as the decoherence properties and their temperature dependencies for the ${}^{3}$H${}_{6}(1){\ensuremath{\leftrightarrow}}^{3}$H${}_{4}(1a)$ transition at 794 nm. It is shown that this material provides very significant improvements in bandwidth, time-bandwidth product, and sensitivity for spatial-spectral holographic signal processing devices and quantum memories based on spectral hole burning. The available signal processing bandwidth for 0.1$%$Tm${}^{3+}$:LiNbO${}_{3}$ is 300 GHz versus 20 GHz for Tm${}^{3+}$YAG. The peak absorption coefficient for 0.1$%$Tm${}^{3+}$:LiNbO${}_{3}$ is 15 cm${}^{\ensuremath{-}1}$ at 794.5 nm compared with 1.7 cm${}^{\ensuremath{-}1}$ for 0.1$%$Tm:YAG at 793 nm, and the total absorption strength is eighty times stronger. The oscillator strength for Tm${}^{3+}$:LiNbO${}_{3}$ is about twenty-five times larger than that for Tm${}^{3+}$:YAG, making the material five times more sensitive for processing high-bandwidth analog signals. The homogeneous linewidth, which determines processing time or spectrum analyzer resolution, is 30 kHz at 1.6 K and 350 kHz at 6 K, as measured by photon echoes. Those values establish potential time-bandwidth products of 10${}^{7}$ and 7 $\ifmmode\times\else\texttimes\fi{}$10${}^{5}$, respectively. The temperature dependence of the homogeneous linewidth was explained by observation of a 7.8 cm${}^{\ensuremath{-}1}$ crystal field level in the ground multiplet and direct phonon coupling. The excited state ${}^{3}$H${}_{4}$ lifetime ${T}_{1}$ is 152 $\ensuremath{\mu}$s and the bottleneck lifetime of the lowest ${}^{3}$F${}_{4}$ level is 7 ms from photon echo measurements. These factors combine to provide a surprisingly large increase in key parameters that determine material performance for spatial-spectral holography, quantum information, and other spectral hole burning applications.

DOI
10.1103/physrevb.85.165106

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Physical Review B•May 15, 2007•19 citations
We report the energy level structure of the 3{}^{3}3H6{}_{6}6​ and 3{}^{3}3H4{}_{4}4​ multiplets for Tm3+{}^{3+}3+ doped congruent LiNbO3{}_{3}3​, as well as the decoherence properties and their temperature dependencies for the 3{}^{3}3H6(1)\ensuremath↔3{}_{6}(1){\ensuremath{\leftrightarrow}}^{3}6​(1)\ensuremath↔3H4(1a){}_{4}(1a)4​(1a) transition at 794 nm. It is shown that this material provides very significant improvements in bandwidth, time-bandwidth product, and sensitivity for spatial-spectral holographic signal processing devices and quantum memories based on spectral hole burning. The available signal processing bandwidth for 0.1%Tm3+{}^{3+}3+:LiNbO3{}_{3}3​ is 300 GHz versus 20 GHz for Tm3+{}^{3+}3+YAG. The peak absorption coefficient for 0.1%Tm3+{}^{3+}3+:LiNbO3{}_{3}3​ is 15 cm\ensuremath−1{}^{\ensuremath{-}1}\ensuremath−1 at 794.5 nm compared with 1.7 cm\ensuremath−1{}^{\ensuremath{-}1}\ensuremath−1 for 0.1%Tm:YAG at 793 nm, and the total absorption strength is eighty times stronger. The oscillator strength for Tm3+{}^{3+}3+:LiNbO3{}_{3}3​ is about twenty-five times larger than that for Tm3+{}^{3+}3+:YAG, making the material five times more sensitive for processing high-bandwidth analog signals. The homogeneous linewidth, which determines processing time or spectrum analyzer resolution, is 30 kHz at 1.6 K and 350 kHz at 6 K, as measured by photon echoes. Those values establish potential time-bandwidth products of 107{}^{7}7 and 7 \ifmmode×\else\texttimes\fi\ifmmode\times\else\texttimes\fi{}\ifmmode×\else\texttimes\fi105{}^{5}5, respectively. The temperature dependence of the homogeneous linewidth was explained by observation of a 7.8 cm\ensuremath−1{}^{\ensuremath{-}1}\ensuremath−1 crystal field level in the ground multiplet and direct phonon coupling. The excited state 3{}^{3}3H4{}_{4}4​ lifetime T1{T}_{1}T1​ is 152 \ensuremathμ\ensuremath{\mu}\ensuremathμs and the bottleneck lifetime of the lowest 3{}^{3}3F4{}_{4}4​ level is 7 ms from photon echo measurements. These factors combine to provide a surprisingly large increase in key parameters that determine material performance for spatial-spectral holography, quantum information, and other spectral hole burning applications.
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The $^{2}F_{7/2}\ensuremath{\leftrightarrow}^{2}F_{5/2}$ optical transitions of Yb3+\mathrm{Y}{\mathrm{b}}^{3+}Yb3+ doped into Y3Al5O12{\mathrm{Y}}_{3}\mathrm{A}{\mathrm{l}}_{5}{\mathrm{O}}_{12}Y3​Al5​O12​ (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^{2}F_{7/2}2F7/2​ and excited 2F5/2^{2}F_{5/2}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^{2}F_{7/2}2F7/2​ to lowest 2F5/2^{2}F_{5/2}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+\mathrm{Y}{\mathrm{b}}^{3+}Yb3+ ions were identified when a magnetic field was applied along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axis, as expected for the D2{D}_{2}D2​ sites in the cubic symmetry crystal, with ground and excited state effective ggg-values of gg=3.40{g}_{\mathrm{g}}=3.40gg​=3.40 (3.34) and ge=1.04{g}_{\mathrm{e}}=1.04ge​=1.04 (2.01), respectively. Together with the convenient diode laser wavelength of this transition, our study suggests that Yb3+\mathrm{Y}{\mathrm{b}}^{3+}Yb3+:YAG is a promising material system for spectral hole burning and quantum information applications.
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