Optical decoherence and energy level structure of 0.1% Tm3+:LiNbO3

We report the energy level structure of the H-3(6) and H-3(4) multiplets for Tm3+ doped congruent LiNbO3, as well as the decoherence properties and their temperature dependencies for the H-3(6)(1) <-> H-3(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+: LiNbO3 is 300 GHz versus 20 GHz for Tm3+ YAG. The peak absorption coefficient for 0.1% Tm3+: LiNbO3 is 15 cm(-1) at 794.5 nm compared with 1.7 cm(-1) for 0.1% Tm:YAG at 793 nm, and the total absorption strength is eighty times stronger. The oscillator strength for Tm3+: LiNbO3 is about twenty-five times larger than that for Tm3+: 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 x 10(5), respectively. The temperature dependence of the homogeneous linewidth was explained by observation of a 7.8 cm(-1) crystal field level in the ground multiplet and direct phonon coupling. The excited state H-3(4) lifetime T-1 is 152 mu s and the bottleneck lifetime of the lowest F-3(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.