The memory effect in the form of hysteresis has been detected in the measured dependence of the intensity of the photon echo in YLiF 4 and LuLiF 4 samples with Er 3+ impurity ions on the orientation, strength, and variation direction of the magnetic field. The prehistory of the location of a sample in the magnetic field with a certain direction and strength is written and stored for no less than 6 h at a temperature of 2 K. The effect crucially depends on the orientation of the optical axis of the sample with respect to the external magnetic field.

The effect of an incoherent photon echo is studied experimentally and theoretically in (LiYFEr3+)-Li-7 crystal ( transition). This is considered as a promising material for Raman optical quantum memory due to the extremely narrow optical transitions. Oscillations of the photon echo intensity versus the external static magnetic field are observed. The theory shows that the oscillation period is very sensitive to one of the parameters of the spin Hamiltonian in the excited state, thereby making the incoherent photon echo convenient for spectroscopic measurements.

The Stark coefficient of the Er 3+ ion in Y 2 SiO 5 is determined for transition). The stark photon echo beating method (SPEB) was used: the pseudo-Stark frequency shift was measured from the period of beats of the temporal form of the photon echo signal. Light beatings were caused by the use of a weak electric field pulse that splits the frequencies of optical transitions of nonequivalent subgroups of echo-active Er 3+ ions in Y 2 SiO5

The Stark coefficient of the Er 3+ ion in Y 2 SiO 5 is determined for transition). The stark photon echo beating method (SPEB) was used: the pseudo-Stark frequency shift was measured from the period of beats of the temporal form of the photon echo signal. Light beatings were caused by the use of a weak electric field pulse that splits the frequencies of optical transitions of nonequivalent subgroups of echo-active Er 3+ ions in Y 2 SiO5

The pseudo-Stark shift in the optical frequency of the 4F9/2–4I15/2 transition of an Er3+ ion in a Y2SiO5 matrix under the action of a weak pulsed electric field is measured from changes in the amplitude and temporal shape of the photon echo.

The physical reasons for observing the splitting of optical lines several orders of magnitude smaller than the spectral width of a laser pulse are investigated. A theory of coherent and incoherent photon echo (PE) in an external static magnetic field and in the presence of a pulsed magnetic field, which causes oscillations of the PE intensity, is elaborated. It is shown that the periods of oscillations in the echo intensity, the echo duration, and the dimensions of the regions in the inhomogeneous line, where the excited ions are coherent, do not depend on the degree of coherence of the laser pulse and on the external static magnetic field. As follows from the theory, in the case of the coherent excitation of the echo, the amplitude of the intensity oscillations is independent of the external static magnetic field if the inhomogeneous line is symmetric. It is shown that the amplitude of the oscillations at the incoherent excitation of the echo is equal to the autocorrelation function of the distribution function of the transition frequency along the inhomogeneous line with the argument equal to the Zeeman splitting of the optical line in the external magnetic field. In this case, the experimental values of the oscillation amplitude are in good agreement with the calculated values of the autocorrelation function for the total inhomogeneous line in LuLiF 4 :Er 3+ ( 4 I 15/2 ⇒F 9/2 transition). In the same way, the autocorrelation function has been obtained for YLiF 4 :Er 3+ on the same transition.

An ultra high-resolution optical spectroscopy technique is proposed for measuring Zeeman and pseudo-Stark frequency splitting during optical transitions. This approach uses the change in the time shape of the echo signal upon a a weak pulse perturbation that splits the optical transition frequencies of two or more echo-active ion subgroups.

A novel scheme for determining the pseudo-Stark splitting of optical lines has been suggested and tested in experiment. The scheme allows one to observe the beating of a photon echo waveform under conditions of overlap in time between a weak electric pulse and its echo- pulse. The pseudo-Stark splitting is equal to the inverse average modulation period of the echo waveform. The photon echo beating of the R1-line in Ruby has been observed. The dependence of the inverse average modulation period of the echo waveform on the average value of the electric field over the optically excited volume has been found. The obtained values of the pseudo-Stark parameter are in good agreement with known literature data.

We have measured the magnetic parameters of a paramagnetic ion in the ground and excited states by controlling the relative phases of excited dipoles with pulse of a weak magnetic field. Er3+ in two crystals LuLiF4 and YLiF4 has been used as a paramagnetic ion. The second matrix was used for control. Optical transition is 4I15/2 → 4F9/2.

A new scheme of the definition of g-factors as ground and excited optical states of a paramagnetic ion in zero external constant magnetic field has been proposed and experimentally realized in optical systems in which the Zeeman effect is manifested. A pulse of a weak magnetic field leads to the occurrence of relative phase shifts of the excited dipoles and, as a consequence, to modulation of a photon echo wave form if the magnetic pulse overlaps in time with the echo pulse. The modulation periods of the wave form depend on polarization of the laser light which excites the photon echo. The values of these periods for sigma- and pi-laser light polarization have been measured and then the g-factors of the ground I-4(15/2) and excited F-4(9/2) states of the Er3+ ion in the LuLiF4 and the YLiF4 matrices have been determined. The g-factor values have been compared with the known literary data.

A relative phase shift between the different groups of excited dipoles, which appears as result of its frequency splitting due to action of a pulse of electric or magnetic fields, depends on a time, if the pulse overlaps in time with echo-pulse. As а consequence, the echo waveform is changed. The echo time form is modulated. The inverse modulation period well enough approximates Zeeman and pseudo-Stark splitting in the cases of magnetic and, therefore, electrical fields. Thus the g-factors of ground 4I15/2 and excited 4F9/2 optical states of Er3+ ion in LuLiF4 and YLiF4 have been measured and pseudo-Stark shift of R1 line in ruby has been determined.

New scheme of definition of g-factors as ground as excited optical states of a paramagnetic ion in zero external constant magnetic field has been proposed and experimentally realized in optical systems in which Zeeman Effect is manifested. A pulse of a weak magnetic field leads to occurrence of relative phase shifts of the excited dipoles and, as consequence, to modulation of a photon echo waveform if magnetic pulse (MP) overlaps in time with echo-pulse. The modulation periods of the waveform depend on polarization of the laser light, which excites the photon echo. The values of these periods for {\sigma}- and {\pi}- laser light polarization have been measured and then the g-factors of the ground 4I15/2 and excited 4F9/2 states of the Er3+ ion in the LuLiF4 and the YLiF4 matrices have been determined. Values of the g-factors have been compared with the known literary data.

A new method of measuring the Curie temperature of a single nanowire located on the surface of an insulating substrate has been proposed. The method is based on the analysis of the current-voltage characteristics of the nanowire obtained at different initial temperatures of the sample. A maximum is observed on the dependence of the first derivative of the resistance on the applied power, the position of which is shifted to lower powers with increasing initial temperature. The Curie temperature is determined graphically as the temperature at zero power. The Curie temperature of a nickel nanowire formed on a SiO2/Si surface by the scanning probe lithography method has been measured. The critical current density at which the transition from the ferromagnetic to the paramagnetic state occurs has been determined.

A method of high-resolution time-resolved optical spectroscopy using oscillations of the photon echo intensity in the presence of a perturbation, which splits the optical frequencies of the transitions of two or more ion subgroups, has been proposed and demonstrated. This method has been applied to systems in which the Zee-man effect is manifested. The transition frequencies of ions are switched by a pulsed magnetic field. Oscillations of the photon echo intensity were observed in LiLuF4:Er3+ and LiYF4:Er3+. The first minimum corresponding to the accumulated phase of the electric dipole moment π/2 is reached in the pulsed magnetic field with an amplitude of ∼2 G at a duration of 30 ns. The Zeeman splitting in this field is ∼10 MHz, which is much less than the laser spectral width (0.15 Å ∼ 9 GHz). The g factor of the 4 F 9/2(I) excited state of the Er3+ ion in the LiLuF4 matrix has been determined in zero magnetic field. The comparison with the g-factor value found from the measurement of the absorption spectrum in a magnetic field of 8 kG has been performed.