Magnetic field- and concentration-dependent photon echo relaxation in ruby with simple exponential decay

Magnetic field- and concentration-dependent, simple exponential photon echo decay in ruby is observed in apparent disagreement with previous work. Similar results are obtained with electron spin echoes.     

Conventional and collision photon echo in ytterbium vapor

The polarization properties of the photon echo generated by two linearly polarized pulses of resonant radiation at the (6s6p)³ P ₁ ? (6s ²)¹ S ₀ transition of ¹⁷⁴Yb are investigated. A complicated polarization behavior of the photon echo versus an angle between the polarization vectors of the excitation pulses is revealed in a mixture of ytterbium vapor with inert gas. For the angles ranging from 0° to 75°, a conventional echo with its linear polarization coinciding with the second excitation pulse dominates and the echo amplitude decreases with an increasing angle. For the angles ranging from 75° to 89°, the photon echo is elliptically polarized. Finally, for an angle of 90°, the conventional echo disappears and the collision echo becomes linearly polarized along the first excitation pulse.     

Photon echo and stimulated photon echo study of various collisional-relaxation channels

Collisional relaxation in SF₆ gas and its mixtures with He and Xe is studied by photon echo and stimulated photon echo methods from the standpoint of the possibility of identifying the contributions of different types of collisions. The nonexponential nature of the kinetic curve of the photon echo is clearly observed for pure SF₆, it is weaker in the mixture SF₆+Xe, and it is virtually completely absent for high degrees of dilution of SF₆ with helium. These features can be explained on the basis of estimates, made from experimental data, of the critical delay between the exciting pulses (for which the nonexponential behavior should be most strongly manifested). In pure SF₆ it is possible to distinguish the contribution of the inelastic channel (rotational relaxation) and the contribution of weak collisions. To distinguish successfully the relaxation channels in mixtures with buffer gases a heavier buffer gas and a much better time resolution must be used. It is shown that data obtained on the orientation and alignment relaxation rates by the stimulated photon echo method can serve as an upper limit for the rates of inelastic processes which cannot be measured by the photon echo method. The combined use of photon echo and stimulated photon echo methods made it possible to obtain data on the cross sections for elastic and inelastic scattering of the collisional pairs SF₆–SF₆, SF₆–Xe, and SF₆–He. Zh. éksp. Teor. Fiz. 116, 47–56 (July 1999)     

TE mode photon echo in slab waveguides

A theory of TE mode photon echo in slab waveguides is developed. It is found that the conditions for generation of a photon echo in waveguides can substantially differ from those in bulk material. For the photon echo in waveguides there is an optimum value of the Rabi frequency, and the echo energy does not depend periodically on the Rabi frequency as in the case of bulk material photon echo. Moreover, it is shown that the capability for echo generation is different for different modes. In particular there are several modes in the waveguide which cannot, in principle, generate an echo.     

Locking of a stimulated photon echo

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 1, pp. 84–88, July, 1991.     

A classical model of the photon echo

An observation and the theory of a nonlinear response in the ensemble of nonlinear classical oscillators excited by two field pulses — similar to the phenomenon of a photon echo in optics — are reported. It has been shown that an echo arises in any ensemble with an inhomogeneously broadened line regardless of the type of interaction with a field (classical or quantum). New peculiarities appear during the determinate distribution of frequencies in the ensemble. On the one hand, an echo pulse is observed with a relatively small (about 100) number of oscillatorsN, on the other, new pulses spaced at a distance that is proportional toN arise in the nonlinear response.     

Time-domain optical data storage by photon echo

Principles and applications of time-domain optical data storage using stimulated photon echo are briefly reviewed. Special emphasis is laid upon the comparison of this memory with holography; both memories use the interference between two optical waves. Some new experimental developments are introduced using samples of europium-ion-doped crystals, one of the most promising candidates in time-domain data storage. Some other topics, such as ultrafast data storage, time-domain data processing, and time- and spatial-image storage using photon echo, are also discussed.     

Excitation of photon echo by noise pulses

The excitation of photon echo by noise pulses that are formed by modulation of the carrying frequency with Gauss noise is modeled. The modeling is based on optical Bloch equations the solution of which for noise pulse realizations is constructed by their stepwise approximation. In terms of the formalism of state transfer matrices, the two- and three-pulse excitation modes are analyzed. The complex envelopes of the primary and stimulated echo responses are determined. In the linear (low-level-signal) mode, the shape of the two-pulse echo corresponds to that of the time delayed and inverted noise pulse. The boundary of the linear mode, upon exceeding of which distortions of the shape of the noise pulse become noticeable, is determined. The shape of the stimulated (three-pulse) echo in the linear mode corresponds to that of the autocorrelation function of the noise pulse realization. Upon passage beyond the boundary of the linear mode, the shape of the three-pulse echo corresponds either to the cross-correlation function of distorted noise pulses (with different intensities) or to the autocorrelation function of distorted pulses (with the same intensities). The modeled photon echo excitation modes can be used in photon echo processors to process signals in the light range.     

Multifrequency photon echo generated by extremely short pulses

A photon echo in a multilevel quantum medium excited by two extremely short pulses with durations of less than one period of oscillation of the light is investigated theoretically. It is shown thatQ echo signals (Q is the number of allowed transitions) can form at each frequency of the allowed transitions, and the number of echo responses for all the allowed transitions equalsQ ². Of these,Q(Q?1) signals are separated in both time and space. The otherQ echo signals of all the allowed frequencies all arise at the time 2τ ₂₁ (τ ₂₁ is the time interval between application of the first and second pulses to the medium) and are collinear with one another.     

Intensity detection of picosecond ruby laser pulses by two photon absorption

The peak intensity of single picosecond light pulses from a mode locked ruby laser and its second harmonic is detected by two photon transmission measurements. The two photon absorption coefficients α⁽²⁾ of the applied crystals CdS and KI are measured (α⁽²⁾_CdS (14400 cm^-1) = 19 cm/GW, α⁽²⁾_KI (28 800 cm^-1) = 8 cm/GW) and calibration curves are presented.     

Three photon ionization of alkali atoms at the ruby laser frequency

Three-photon ionization cross sections of alkali atoms for linearly and circularly polarized light have been calculated using the Green's function and the quantum defect methods. The results are compared with the values experimentally obtained by Cervenan et al.     

Long-lived stimulated photon echo in optically thick van vleck paramagnets

Long-lived stimulated photon echo (LSPE) excitation by the sequence ofN pulse pairs in optically thick LaF₃:Pr³⁺ crystals is investigated numerically. Hyperfine structure of the ground and excited states of medium atoms is taken into account. Stable LSPE amplification along the total sample length is realized in the case when the total initial area of the pulse sequence is larger than the threshold value π. Cumulative effect depends on the threshold conditions and the crystal length. At measuring medium spectroscopic parameters the large evaluation errors can be introduced due to neglect of light propagation effects.     

The effect of instantaneous diffusion on the relaxation of photon echoes in ruby

It has been recently suggested that electrid dipole instantaneous diffusion plays an important role in the relaxation of photon echoes in ruby. Our experiments indicate that instantaneous diffusion is not important in this relaxation.     

Femtosecond photon echo in dye-doped polymer films at room temperature

The signals of primary and stimulated femtosecond photon echo in polymer films doped with dye (phthalocyanine) molecules have been experimentally investigated at room temperature. A femtosecond echo spectrometer for these echo experiments is described. The decay curves of echo signals with increasing time intervals between excitation femtosecond pulses are obtained and blue shifts of the spectra of femtosecond echo signals with respect to the spectrum of excitation pulses are revealed. The possibilities of using the studied doped polymer films as recording media for high-temperature echo processors and coolants in optical refrigerators are analyzed.     

Stimulated photon echo under excitation by incoherent and coherent pulses

Excitation of stimulated photon echo by two incoherent pulses obtained from one source and one coherent pulse is considered. The dependence of the average amplitude of stimulated echo on the parameters of noise pulses is determined. The results can be used for analysis of the corresponding algorithm of excitation of stimulated spin echo, as well as in calculations of characteristics of the signal processors based on the phenomena of photon and spin echoes.