Collision-induced photon echo at the transition0↔1in ytterbium vapor: Direct proof of depolarizing collision anisotropy

Abstract

A collision-induced photon echo arising at the transition 0 ↔ 1 of ytterbium in the presence of heavy atomic buffer is investigated. Collision-induced echo signal appears in the case of mutually orthogonal linear polarizations of exciting pulses and it is absent without buffer. Collision-induced echo power grows with buffer pressure up to the maximum value and decays exponentially at further buffer pressure growth. Collision-induced echo power is essentially less than that of the ordinary echo generated by pulses with parallel polarizations in the same mixture, and its polarization is linear with the polarization vector directed along that of the first exciting pulse. All the properties of collision-induced photon echo are explained on the basis of collision relaxation dependence on the direction of active atom velocity.

Collision-induced stimulated photon echo at the transition 0–1

“…At small τ 2 intervals (| (2) b − (1) b |τ 2 1), the echo amplitude is proportional to | (2) b − (1) b |. The collision-induced stimulated photon echo, proposed in the present paper, has much in common with the twopulse collision-induced photon echo, observed in ytterbium vapour [35], though there are some essential differences. First, the two-pulse echo is determined by the difference in the two relaxation characteristics of the resonant transition, while the stimulated echo is determined by the difference in the relaxation characteristics of the excited level.…”

“…Generally, the relaxation processes act to decrease the amplitude of the echo signals, however in some cases, when the conventional echo is locked, the relaxation may act to break the lock and produce the relaxation-induced echo signals. Such a collision-induced two-pulse photon echo was recently observed in ytterbium vapour on the transition J a = 0 → J b = 1 [35]. This echo appears due to the difference in the relaxation rates of the two components of the atomic dipole moment-collinear with the atomic velocity and perpendicular to it.…”

“…In the experiment [17], the intensity of the modified stimulated photon echo formed in ytterbium vapour on the transitions J a = 0 → J b = 1 → J c = 1 was reduced greatly when the polarizations of all three excitation pulses became collinear, which was interpreted in [38] as a collision-induced echo. Inspired by the experiment [35], we propose here a scheme, much simpler than that in [36,37], for observation of the collision-induced stimulated photon echo on a single transition J a = 0 → J b = 1. In this case, only three nondegenerate states are involved in the echo formation-the lower level and the two substates of the upper level, so that the stimulated photon echo generally contains all types of echoes characteristic of three-level systems-the conventional twolevel stimulated echo, the modified stimulated echo and the tri-level echo.…”

174Yb3P1level relaxation found via weak magnetic field dependence of collision-induced stimulated photon echo

“…This effect, known as 'wind effect' [20], can hardly be detected in the experiments in the Dopplerfree saturation spectroscopy even for relatively simple transition 0 ↔ 1. However, the 'wind effect' reveals in the collisioninduced photon echo at this trans ition, as predicted in [21] and detected in [17,22]. To detect CPE without a background of conventional photon echo, a pair of exciting radiation pulses, polarized linearly and mutually orthogonal, were used.…”

“…In the absence of col lisions, the macroscopic polarization generated by the first exciting pulse is orthogonal to the polarization of the sec ond exciting pulse, and an echo can not appear. In a gaseous mixture of active atoms with buffer atoms, the anisotropy of collision relaxation creates a small orthogonal polarization component, and the second exciting pulse can generate the collisioninduced PE signal [17,22].…”