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.     

Oscillations in radioactive exponential decay

Several older and recent reports provided evidence for the oscillatory character of the exponential decay law in radioactive decay and attempted to explain it with basic physics. We show here that the measured effects observed in some of the cases, namely in the decay of ²²⁶Ra, ³²Si in equilibrium, and ³⁶Cl, can be explained with the temperature variations.     

Higher order Gamow states with exponential decay

We derive Gamow vectors fromS-matrix poles of higher multiplicity in analogy to the Gamow vectors describing resonances from first-order poles. With these vectors we construct a density operator that describes resonances associated with higher order poles that obey an exponential decay law. It turns out that this operator formed by these higher order Gamow vectors has a unique structure.     

Determination of phase fluctuations of a Highly-Stabilized laser by the analysis of photon echo decay functions

The simple 2-pulse echo as a prototype of coherent spectroscopy offers the unique possibility for a recall of past time parameters. This feature is utilized in the optical frequency domain for the realization of a phase comparator, equivalent to an optical interferometer of approximately 10 km variable path length difference. The measured autocorrelation time of the optical field is a convenient absolute measure of the frequency stability of the laser field and has been tested in the 10–100 kHz line width range.     

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.     

Motions of the flux lines in high-T c superconductors from NMR linewidth,relaxation and spin echo decay

The motion of the flux lines (FL) in high temperature superconductors and their relationship with the NMR quantities are reviewed and discussed in the light of recent⁸⁹Y NMR experiments in YBCO-type compounds. In particular measurements involving the⁸⁹Y spin echo attenuation induced both by the thermal excitation of the FL’s and by motions driven by DC current and pulsed magnetic fields are presented, with preliminary results and lines of interpretation. Flux line motion as observed with¹⁹⁹Hg NMR in HgBa₂CuO_4+δ high temperature superconductor is discussed.     

Nonexponential decay in relaxation phenomena

A variety of considerations from different points of view including non-Markovian stochastic processes, basic quantum mechanics, and a mechanism based on condensed matter physics, all lead to the fractional exponential decay at long times in relaxation processes. Implications of this decay law and its verifiable predictions in a broad range of phenomena in condensed matter physics are pointed out.     

Stimulated photon echo with temporal data coding in the Hopfield-Little regime

A model of an optical neural network with associative memory using stimulated photon echo (SPE) with temporal data coding is presented. The electrical field’s calculation of the SPE signals is carried out for case of multiple influences on the resonant medium by optical pulses. A computer model of an optical echo processor with associative retrieval of information is elaborated.     

Deviations from exponential decay in quantum mechanics

The usual quantum mechanical explanation of exponential decay is not exact. The approximations made lead to an average lifetime which can also be obtained directly using Fermi's Golden Rule. The question whether or not quantum mechanical decay is always exponential was recently raised again in connection with the possible decay of the proton. In this paper we derive a new criterion for the length of the non-exponential decay era. A formalism for general quantum systems is used to derive an exact expression for the survival probability in terms of a spectral density function. This expression is used for numerical studies. We find that in general, for short times, the decay is not exponential. In some cases a quadratic law is followed instead.     

Excitation of photon echo by pulses modulated with Barker codes

The excitation of the primary and stimulated photon echoes by pulses modulated in phase with Barker codes is modeled. The shape of the complex envelopes of the primary and stimulated echoes is found by solving the optical Bloch equations. Linear and nonlinear excitation modes are considered. In linear modes, it is possible to realize a time delay and form the correlation function of modulated pulses. The results obtained can be used in modeling and analyzing the corresponding algorithms of the photon echo excitation and in calculating the characteristics of signal processors based on the phenomena of photon and spin echoes.     

Electron spin echo modulation and relaxation in polythiophene

Electron spin echo measurements on neutral poly (thiophene) show a clear modulation of the spin-echo decay. Analysis of the modulation and its Fourier transformed (ω) power spectrum indicates that the wave function of the spin defect is extended over ～ 25 proton nuclei. The functional behavior of the longitudinal relaxation, T₁, versus temperature is very similar to that observed previously for (CH)_x, although T₁ values for poly (thiophene) are significantly longer.     

Modified stimulated photon echo with hyperfine structure of resonant levels

The intensity and polarization of a modified stimulated photon echo generated on resonant levels with hyperfine structure are obtained. It is proposed that the polarization properties of this kind of a photon echo can be used for the identification of the structure of the resonant transitions on which the echo is formed as well as for the separation of the modified stimulated photon echo pulse from the third exciting pulse.     

Allowance for irreversible relaxation in echo spectroscopy

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 2, pp. 296–302, February, 1988.