Abstract:The results of an experimental investigation of the incoherent photon echo in ruby (with Cr 3+ concentration equal to 0.16 wt%) at T = 1.7 K are presented. Optical fiber with length 3 m and diameter 100 µm was used for delivery of the first exciting pulse to a sample. The dependence of the IPE intensity on the excitation wavelength within the width of R1 absorption line was studied. The IPE decay curve was obtained and the phase relaxation time was found to be equal to 98 ns. Oscillogram of incoherent backward photon echo (IPE) in concentrated ruby. The IPE signal is the first one at the right. The other pulses are the signals of diffraction corresponding to the first and the second exciting laser pulses

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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...