Theoretical and experimental studies of the photon and stimulated photon echo generated at the transition 0-1 of Yb-174 atoms are reviewed. Analogues of the phenomena induced by collisions of Yb-174 atoms with buffer gas atoms are also considered. The nature of collisions is analyzed.

Experimental data have been obtained for the relaxation rates of population, orientation, and alignment of the 174 Yb(6 s 6 p ) 3 P 1 level due to collisions of 174 Yb atoms with atoms of noble gases.

For the first time, a complete set of decay parameters, due to collisions of 174Yb atoms with noble gas atoms and with ytterbium atoms, was experimentally found for the 174Yb (6s6p) 3P1 level. The method of stimulated photon echo with special angles between the polarization vectors of light pulses forming an echo at the 174Yb (6s2) 1S0—(6s6p) 3P1 transition (type 0↔1 ) is used. For each buffer gas of He, Ne, Ar, Kr, Xe, and Yb, the decay rate constants of population, orientation and alignment for the collision destruction of the 3P1 level of 174Yb atoms are determined. All the decay rates demonstrated their linear increase with a buffer gas pressure, and the corresponding relaxation constants are determined. Each of the indicated relaxation constants, as well as the difference between the alignment and orientation relaxation constants, increases with the increasing buffer gas mass.

The nonmonotonic kinetics of a collision-induced photon echo has been investigated for a number of buffer atoms. The collision-induced photon echo was generated at the 174 Yb (6 s 2 ) 1 S 0 ↔ (6 s 6 p ) 3 P 1 (0 ↔ 1) transition by a pair of linearly and mutually orthogonally polarized resonant radiation pulses in ytterbium vapor and its mixtures with He, Ne, Ar, Kr, and Xe. The kinetics of the conventional photon echo generated by pulses with identical linear polarizations was recorded in the same mixtures. The derived decay rate constants for both types of echo are equal to within the measurement errors. For the collisions of 174 Yb atoms between themselves and with other ytterbium isotopes in a natural mixture of isotopes, an upper limit for the anisotropy parameter has been estimated, 0.22 ± 0.07 of the photon echo signal decay rate.

A collision-induced photon echo (PE) was formed at the Yb-174 (6s(2)) S-1(0)-(6s6p) P-3(1) transition by two resonant radiation pulses polarized linearly and mutually orthogonally. The noble gases He, Ne, Ar, Kr and Xe were used as collision partners for excited Yb-174 atoms. The nonmonotonous decay kinetics of collision-induced PE was detected. The ordinary PE formed by identical linear polarization pulses at the same experimental conditions showed a monotonous decay for the time delays between 80 and 300 ns. The anisotropy parameters for the collisions of Yb-174 atoms with Ne, Ar, Kr and Xe atoms increase with the buffer atom mass and are between 15% and 20% of the corresponding homogeneous line broadening values.

Collision-induced stimulated photon echo generated at transition 0 <-> 1 was analyzed theoretically and investigated experimentally in the gaseous mixture of ytterbium vapour diluted with a large amount of buffer gas xenon in the presence of a weak longitudinal magnetic field. The inter-combination transition of Yb-174 (6s(2)) S-1(0) <-> (6s6p) P-3(1) was used; all experimental parameters were carefully controlled for their correspondence to the broad spectral line conditions. The curve representing the collision-induced stimulated photon echo variations versus a weak magnetic field strength showed very good agreement with the corresponding theoretical curve; this agreement permitted getting the decay rates for Yb-174 level P-3(1) orientation and alignment in collisions with Xe.

The photon echo formed at the intercombination (6s(2)) S-1(0) <-> (6s6p) P-3(1) (type 0-1) transition of ytterbium atoms Yb-174 by two pulses of resonance radiation was investigated as a function of the time delay between exciting pulses (the photon echo kinetics). For exciting radiation pulses of the same linear polarization in the delay region 70-250 ns, the photon echo kinetics is close to the exponential one both in pure ytterbium and in its mixtures with buffer gases Ar and Xe. The relaxation cross sections were determined for all three cases, taking into account the isotopic composition of xenon and ytterbium. For the first time, the complex nonmonotonous kinetics of the collision-induced photon echo was observed in the same mixtures for the forming pulses of linear mutually orthogonal polarization. The relative efficiency of buffer atoms Yb (other isotopes than Yb-174), Xe and Ar in the collision-induced photon echo formation was obtained.

A new idea based on the collision-induced stimulated photon echo in the presence of weak longitudinal magnetic field is applied to the depolarizing collisions research in a gaseous mixture of ytterbium vapour with xenon. Comparison of experimental data with theoretical prediction for the collision-induced stimulated photon echo in the weak magnetic field shows that the alignment decay rate of state 3P1 in 174Yb is higher than the orientation decay rate.

It was shown experimentally in ytterbium vapour at the transition (6s(2)) S-1(0) (6s6p) P-3(1) (type 0 <-> 1), that the weak longitudinal magnetic field destroys the collision induced two-pulsed photon echo generated in a gas mixture with heavy atomic buffer; in agreement with theoretical prediction.

Our research into photon echo (PE) and stimulated photon echo (SPE) in ytterbium vapour at the transition 0 ↔ 1 is summarized. We present the polarization properties of PE and SPE in pure gas, anisotropy of collision relaxation, collision-induced PE and collision-induced SPE.

Experimental results were obtained at the inter-combination transition (6s(2)) S-1(0) <-> (6s6p) P-3(1) (type 0 <-> 1) of Yb-174 vapour for several combinations of linear and circular polarizations of three exciting pulses. A peculiar case appears when the first pulse has linear polarization crossed with the polarizations of the second and third exciting pulses: the stimulated photon echo (SPE) does not appear in pure ytterbium; dilution of ytterbium by Xe implies a collision induced SPE with non-monotonic amplitude dependence on buffer pressure, and with polarization along the first exciting pulse. For circular polarizations, when the first exciting pulse has polarization opposite to the circular polarizations of the second and third pulses, the SPE does not appear either in pure ytterbium vapour or in its mixture with a heavy atomic buffer. SPE polarization dependence on the third exciting pulse area was demonstrated. This result may be of interest for optical data processing. All the results agree with theoretical predictions.

Collision-induced photon echo generated in ytterbium vapour at the transition (6s2) 1S0 ↔(6s6p) 3P1 (transition of the type 0 ↔ 1) was investigated in the presence of the longitudinal magnetic field strength between zero and 5.6 G. For the weak magnetic fields, not over 0.27 G, the collision-induced echo signal decreases with magnetic field increase. Further increase of the magnetic field strength reveals oscillatory behavior of the echo signal. Experimental results are in qualitative agreement with theoretical predictions.

The polarization of the stimulated photon echo (SPE) generated in a gas at the 0↔1 transition was analysed for the first time for all combinations of three linearly polarized resonant radiation exciting pulses. Experimental results were obtained for the SPE generated at the inter-combination transition (6s2) 1S0↔(6s6p) 3P1 of 174Yb (type 0↔1). In the case where one of the exciting pulses had linear polarization crossed with that of the other two exciting pulses, the SPE polarization proved to be linear and parallel to the crossed pulse polarization. When the second and third exciting pulses had linear polarizations crossed with that of the first one, no SPE in pure ytterbium appeared. For high dilution of ytterbium with the Xe atomic buffer, a collision-induced SPE appeared and showed a non-monotonic amplitude dependence on the buffer pressure and a polarization coinciding with the polarization of the first pulse.

For the first time, stimulated photon echoes (SPE) generated in a gas at the transition 0↔1 by circularly polarized resonant radiation pulses were analysed both theoretically and experimentally. Experiments were performed for the inter-combination transition (6s2) 1S0↔ (6s6p) 3P1 of 174Yb (type 0↔1). The SPE generated by three radiation pulses of identical circular polarizations has the same circular polarization. When the second or the third exciting radiation pulse has a circular polarization opposite to that of the other two pulses, the SPE polarization coincides with that of the oppositely polarized pulse. Finally, when the first exciting radiation pulse has a circular polarization opposite to the circular polarizations of the second pulse and third pulse, the SPE does not appear either in pure ytterbium vapour or in its mixture with a heavy atomic buffer.

Situations when a set of resonant radiation pulses can not create photon echo (PE) or stimulated photon echo (SPE) at relatively simple optically allowed transition in a gas are investigated. Some cases when dilution by atomic buffer can imply PE or SPE generation are analyzed. Discovered experimentally mechanisms, amplitudes, and polarization properties of these collision induced PE and collision induced SPE are in agreement with theoretical predictions. Dynamic Stark suppression of photon echo is also studied.

Photon echo generated at the inter-combination transition (6s 2) 1 S 0 − (6s6p) 3 P 1 of 174Yb was investigated for pure ytterbium vapor and for its mixtures with atomic buffers. In pure ytterbium vapor, the polarization of photon echoes at this 0–1 transition coincides with the polarization of the second exciting pulse for all combinations of linear and circular polarizations of exciting radiation pulses. Photon echo does not appear either for linear orthogonal or for opposite circular polarizations of exciting pulses in pure ytterbium. In mixtures of ytterbium with atomic buffers (Kr, Xe), collision induced photon echo arises only for exciting pulses of linear orthogonal polarizations, its power is essentially less than that of the ordinary echo generated by pulses with parallel polarizations in the same mixture. Polarization of collision induced echo is linear, and it coincides with polarization of the first exciting pulse. Experimental results agree with calculations, and they confirm that the collision induced photon echo at this transition arises exclusively due to anisotropy of depolarizing collisions.

Polarization properties of photon echo generated at the inter-combination transition (6s(2)) S-1(0) <-> (6s6p) P-3(1) of Yb-174 (transition of type 0 <-> 1) are for the first time investigatedexperimentally for a complete set of polarizations of two exciting pulses of resonant radiation (linear-linear, circularlinear, linear-circular, and circular-circular) in a pure ytterbium vapor. In all cases the photon echo polarization coincides with polarization of the second exciting pulse. Photon echo in a pure gas does not appear neither for exciting pulses of mutually orthogonal linear polarizations, nor for the pulses of opposite circular polarizations. Experimental results are in agreement with theoretical predictions. (C) 2011 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA