Acta Physica Sinica

THEORETICAL STUDY OF NON-EXPONENTIAL PHOTON ECHO DECAYS

WANG HAI-YU, Huang Shi-Hua, 中国科学院长春物理研究所激发态物理开放实验室

Published Jan 1, 1997• 0 citations

Abstract

Photon echo decays of several impurity paramagnetic ions are calculated,the historical average of each lattice nuclear spin flip is described by a bivalued random telegraph process,and the spatial average is obtained according to the crystal structure. The results are very close to those of Monte Carlo simulations. From the experimental observations,we obtained that all samples have a universal decay form.

DOI: 10.7498/aps.46.1108

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Acta Physica Sinica

THEORETICAL STUDY OF NON-EXPONENTIAL PHOTON ECHO DECAYS

WANG HAI-YU, Huang Shi-Hua, 中国科学院长春物理研究所激发态物理开放实验室

Published Jan 1, 1997• 0 citations

Publisher

Abstract

DOI: 10.7498/aps.46.1108

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Physical review. B, Solid stateJun 1, 197238 citations

Nonexponential photon-echo decays are observed in ruby,

{\mathrm{Er}}^{3+}

{\mathrm{YLiF}}_{4}

, and

{\mathrm{Er}}^{3+}

{\mathrm{LaF}}_{3}

with samples of low ion concentrations in high (10--50 kG) magnetic fields. At the highest fields, photon-echo decays are field independent and their temporal forms are identical for all three systems. This behavior is attributed to optical dephasing arising from electron-spin nuclear-spin superhyperfine interactions in the presence of a frozen core.

{\mathrm{Pr}}^{3+}

{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}

and show experimental measurements of population decay of the ground state hyperfine levels at $\ensuremath{\sim}2$ K. We also present a method to measure rates of individual transitions from hole burning spectra that requires significantly fewer fitting parameters in theoretical rate equations compared to earlier work. Furthermore, we measure the effect of external magnetic field on the flip-flop rates and observe that the rates slow down by two orders of magnitude in a field of 5--10 mT.

{)}^{\mathit{d}}

] agrees with the results of numerical simulation, although it does not agree with the existing results of physical experiment. We believe that such a disagreement is of a fundamental nature and manifests a basic need for further experimental and theoretical work.

A detailed experimental study is reported of the decay of circularly polarized photon echoes as a function of Cr concentration in samples ranging from 0.006 to 1.2 wt.%

{\mathrm{Cr}}_{2}

{\mathrm{O}}_{3}

{\mathrm{Al}}_{2}

{\mathrm{O}}_{3}

. The decay is found to be independent of temperature in the liquid-helium range and generally depends on the pulse separation $\ensuremath{\tau}$ as $\mathrm{exp}(\ensuremath{-}K{\ensuremath{\tau}}^{\frac{1}{2}})$ with the decay constant

K

proportional to the square root of the Cr concentration. The measured decay is independent of external magnetic field in the range 1.5-6 kG except at 1.06 kG, where modified decays are observed. A theoretical analysis is made of photon-echo decay in terms of spin flips of echo ions resulting from Cr-Cr magnetic interactions and yields good agreement with the observed decays. Spectral diffusion, modified for photon echoes, is shown not to be an important effect. However, anomalously slow decay is observed in some samples when the laser is tuned to the long-wavelength tail of the sample absorption line and the spectral-diffusion mechanism may apply here. The photon-echo-decay measurements are compared with spin-resonance and available spin-echo data in ruby. Also, it is inferred that resonant optical energy transfer is not an important photon-echo-decay mechanism even in the darkest sample studied.