We studied the effect of the static magnetic field on the behavior of the photon echo in LiLuF 4 :Er 3+ in [1]. The dependence of the photon echo intensity on the magnitude and direction of the static magnetic field H dc can be qualitatively explained as follows [1][2][3][4][5]. The first pump laser pulse changes the orientation of the magnetic field on the neighboring nuclei. As a result of the reorientation, the neighboring nuclei that were polarized along the field H dc + H g start to precess around the new direction H dc + (H g + H e )/2. Here, H g and H e are magnetic fields produced on the fluorine nucleus by the magnetic moment of the Er 3+ electron that is in the ground and excited states, respectively. The precession of the neighboring nuclei modulates the magnetic field on the Er 3+ ion and, consequently, modulates the distance between the energy levels of the ion. As a result, the relative phase shift of the elec tric dipole Er 3+ after the first pump pulse differs from the shift after the second pulse if the oscillation period does not coincide with the delay time between the laser pulses. This leads to the oscillation of the echo enve lope. With the increase in the number of the neighbor ing nuclei with different precession frequencies (H dc is perpendicular to the C axis of the crystal), the echo signal decreases due to the destructive interference. In the case of the pulsed magnetic field applied at the instant of the echo formation (between the first and second laser pulses or between the second laser pulse and the echo pulse), the phase difference should not necessarily be nonzero. A substantial effect of the weak pulsed magnetic fields on the echo parameters is expected in this case. This was shown by the first experiments [6] we performed with LiLuF 4 :Er 3+ for several values of the amplitude and duration of the pulsed magnetic field h perpendicular to the C axis of the crystal (h ⊥ C).In this work, the measurements were performed in LiLuF 4 :Er 3+ and LiYF 4 :Er 3+ at the parallel orientation (h || C). In this orientation, a significant decrease in the photon echo intensity is observed already at the values h ~ 1.7 G, which are an order of magnitude less than those at h ⊥ C (~12 G). With increasing h, starting from a certain value, which is inversely proportional to the magnetic pulse duration, the echo intensity starts to increase. The dependence of the photon echo intensity on the amplitude h is oscillatory. The oscilla tion period is determined by the magnetic pulse area. Physically, this is related to the fact that the optical fre quencies of the erbium ions, the ground states of which have the spin projections S z = ±1/2, are split in the pulsed magnetic field owing to the Zeeman effect. The accumulated phases, i.e., phases of the electric dipole moments of these two groups of ions acquired during the time τ h of the action of the magnetic pulse, have different signs and are proportional to the mag netic pulse area. The resulting electric dipole moment and the echo intensity are proporti...

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Abstract:It is reported about the first observation and studying of the photon echo in LuLiF 4 :Er 3+. The energy transition is 4 I 15/2 → 4 F 9/2 (λ = 6536Å). The density of ErF3 is 0.025 wt%. The operation temperature is 1.9 K. Measurements were spent at low (up to 1200 Oe) and even zero external magnetic fields. It was studied a behavior of the photon echo intensity versus the magnetic field magnitude and direction about the crystal axis C and versus the laser pulse separation t 12 . It was observed an exponential growth and then, after some plateau, an exponential decreasing of the photon echo intensity as a function of magnetic field with increasing of the magnetic field from zero value. The parameters describing the exponential growth and decreasing are not depended on direction of magnetic field. Value of a magnetic field at which the echo intensity accepts the maximum, and quantity of this maximum decrease with increased the pulse separation t 12 and the angle θ between the magnetic field and crystal axis. The echo intensity exponentially decreases with increased θ. The parameter describing the exponential decreasing is not depended on the magnitude of the field. The echo intensity as a function of pulse separation shows exponential decay. The phase relaxation time is depended on the magnitude and direction of the magnetic field. T 2 is equal to 202±16 ns at zero magnetic field. Phenomenological formula is suggested, which qualitatively presents the mentioned dependencies. Polarization properties of the backward photon echo in this crystal are studied also. Echo size versus magnetic field directed as along optic axis as at an angle of θ = 5• for different values of t 12 . The color symbols show experimental points. The solid curves were calculated using expression (1). The Y-scale is logarithmic