V N Ishchenko

Velocity effects in atomic and molecular collisions: Study by coherent transients

The effect of translational velocity of active atoms and molecules on the properties of photon echo is investigated using the technique of coherent transient processes. A variation in the photon-echo decay with a frequency detuning of the excitation radiation relative to the center of the vibrational-rotational transition 0 ↔ 1 ν3R(4, 3) is observed in a mixture of 13CH3F with atomic buffers. The results are interpreted using the dependence of the echo decay rate on the magnitude of the translational velocity of active particles. The dependence of the relaxation matrix on the direction of the velocity of active atoms results in a new phenomenon of the collision-induced echo, which is investigated at the transition 0 ↔ 1 174Yb in mixtures with atomic buffers.

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)3P1 ↔ (6s2)1S0 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.

Effect of magnetic field on the stimulated photon echo in ytterbium vapors

Polarization of the stimulated photon echo (SPE) at the 0 ↔ 1 transition in ytterbium vapors in the presence of a longitudinal magnetic field of 0–40 G is experimentally and theoretically studied. The SPE is generated using three light pulses with identical linear polarizations, so that the SPE polarization is the same at zero magnetic field. In the presence of a weak magnetic field, the SPE polarization vector rotates around the magnetic field vector and the depolarization of the SPE signal takes place. Each of the SPE polarization components exhibits biharmonic oscillations depending on the magnetic field. In the presence of a strong magnetic field, these oscillations vanish and the SPE becomes depolarized. The experimental data are in qualitative agreement with the results of the numerical calculations performed with the method of the evolution operator for the finite-duration excitation pulses. The application of the results for the processing of optical data is discussed.

Collision-induced photon echo in ytterbium vapour at the transition 0–1: magnetic field effect

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.

Depolarizing collisions in ytterbium vapor: Isotropic and anisotropic relaxation

Isotropic depolarizing collisions are studied using a stimulated photon echo with a specific polarization of the excitation radiation pulses in a mixture of ytterbium with krypton for the J = 1 ⇄ J = 0 transition of 174Yb. The difference between the relaxation rates of orientation and alignment γb(2) − γb(1) of the 3P1(6s6p) 174Yb level is measured as a function of the krypton pressure. The collision photon echo at the J = 1 ⇄ J = 0 transition induced by the anisotropic relaxation is studied for the Yb + Xe mixture. The power of the collision echo increases from zero with the addition of a buffer gas to ytterbium, reaches an optimal level, and decreases with an increase in the buffer gas pressure. The polarization of this collision-induced echo differs from the polarization of the conventional echo. The experimental results are in qualitative agreement with theoretical predictions.

Collision induced two-pulsed photon echo at the transition 0–1 in a weak longitudinal magnetic field

It was shown experimentally in ytterbium vapour at the transition (6s2) 1S0 (6s6p) 3P1 (type ), 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.

Polarization of the stimulated photon echo in ytterbium vapour at the transition 0 ↔ 1

Experimental results were obtained at the inter-combination transition (6s2)?1S0 ? (6s6p)?3P1 (type 0 ? 1) of 174Y b 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.

The stimulated photon echo generated by linearly polarized exciting pulses at the 0?1 transition in ytterbium vapour

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.

Stimulated photon echo at the transition 0–1 in ytterbium vapour: circular polarizations

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.

Polarization echo spectroscopy of the 0 ? 1 transition in ytterbium vapour

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.