Dynamic Interaction between Paramagnetic Ions and Resonant Phonons in a Bottlenecked Lattice

Abstract

Anomalous behavior is observed in the time dependence of paramagnetic relaxation for dilute cerous magnesium nitrate at Zeeman frequencies of 11 GHz, temperatures 1.2-4.2°K, and nominal cerium concentrations of 0.2%. Immediately after excitation of the paramagnetic transition to a negative spin temperature, direct relaxation is accompanied by heating of the resonant lattice modes, and a "phonon avalanche" occurs. The decay profile of the center of the paramagnetic resonance line is distorted in a characteristic manner, and certain peculiarities in the shape of the line appear. Later in the decay, after the spin temperature has become positive, the decay approaches the behavior customarily identified with a phonon bottleneck, and the line shape becomes normal. The avalanche builds up on a time scale of microseconds, while the decay at positive spin temperature requires tens of milliseconds. Concentration, size, and surface effects are found. A simple theoretical model is developed and shown to agree qualitatively, but not quantitatively, with experiment. 157 3 J. A.

Properties ofQswitches with partial polarizers

“…In agreement with Mims and Taylor (1971) the equations for (Sz)' and (nQ)' coincide with those of Brya and Wagner (1967). These equations can be written in terms of the following quantities used by Brya and Wagner:…”

Superfluorescence and amplified spontaneous emission of 29-cm−1phonons in ruby

“…found for A7Vo = 6.5x 10 17 cm time at / =0 is then TR ^ 110 ps, and the corresponding L c ~ 3.8 jxm. All the features familiar from optical superfluorescence clearly emerge, particularly the charThe best agreement is " 3 and phonon occupation numbers, given the initial inversion density A7V 0 . In calculating pit), the effect of the probe pulse is incorporated by properly augmenting the inversion density at time t\i.…”

“…1 By contrast, the acoustical analog, i.e., superfluorescent emission of phonons, has not been observed up until now, although its existence was suggested. 2 Evidence for incoherent phonon avalanches is available, 3 but only scarce as concerns phonons of frequencies beyond ultrasound (> 30 GHz). 4 " 7 In this Letter, we report on the first observation of superfluorescence of high-frequency phonons, and further show that by suitable modification of the conditions the emission becomes incoherent.…”

“…Equation (3) has been fitted to the data beyond / J2 = 150 ps with ATVo as an adjustable parameter. The result of the fit is presented in the inset of Fig.…”

Phonon Bottleneck Investigation Using a Quantum Statistical Method

“…There are also experimental results which suggest a time dependence of Av during the decay of a nonequilibrium state of a crystal with a phonon bottleneck [3]. I n order to shed some light into these obscurities it would be necessary to develop a general theory of the relaxation of a crystal with a phonon bottleneck which allows the estimation of all parameters from first principles.…”