Search

The possibility exists for improving the present experimental constraint on the tensor coupling constant in radiative pion decay by at least a factor of six. The method emphasizes relative decay probabilities rather than absolute rates.

The connection of rare decays to supersymmetric grand unification is highlighted, and a review of the status of rare decay experiments is given. Plans for future investigations of processes that violate lepton flavor are discussed. A new result from the MEGA experiment, a search for {mu}{sup +} {yields} e{sup +} {gamma}, is reported to be B.R. < 3.8 x 10{sup -11} with 90% confidence.

The delay time of the principal superradiance pulse is found theoretically for the cases when a longitudinal wide-band pump pulse is long on the time scale of the output radiation or when such a pump pulse travels along an active medium more slowly than the optical wave. A comparison is made of the delay times of the forward and reverse waves. A linearized semiclassical problem (one-dimensional case) with a random source is solved for the amplitude of the radiation field.

It is shown that the asymmetric nature of the radiation emitted by a self-terminating neon laser (? = 614.3 nm) is a consequence of the propagation of ionizing potential gradient waves that ensure the traveling nature of the excitation of a gas. A solution of the Maxwell-Bloch equations yields formulas relating the delay between the appearance of superradiance pulses from the opposite ends of a source to the velocity of propagation of these waves. Estimates obtained of the velocity of propagation of ionizing potential gradient waves in neon are in agreement with the available experimental data.

A study is made of the dynamics of a superradiance pulse in a transversely inhomogeneous active medium inside a tubular waveguide with dielectric walls. The problem is solved numerically in the approximation of a given field profile by expanding the radiation field in terms of the normal modes of the waveguide and the polarization and inversion of the medium in terms of basis functions dependent on the transverse coordinates. It is shown that an inhomogeneous transverse distribution of the field and of the initial inversion can suppress the appearance of oscillatory replicas (superradiant ringing) of the main superradiance field and also can result in incomplete utilization of the energy stored in the active medium because of coherent dephasing of the polarization of the medium in different parts of a transverse cross section of the waveguide.

A semiclassical method is used to study cooperative spontaneous radiation (superradiance) emitted from an excited medium in a thin dielectric waveguide subject to an allowance for the highest-Q normal wave in the waveguide (constant profile fields). A radiation pulse is described by a nonlinear equation which represents weakening of the interaction between matter and a field of constant profile in the case of a large-area pulse. This results in partial utilization of the stored energy, reduces the steepness of the edges of a pulse and its maximum intensity, and suppresses oscillation replicas.