Search

Excitation of induced coherent Smith-Purcell (SP) radiation by relativistic magnetized electron beam in the absence of the resonator is considered within the framework of the dispersion equation. We have found that the dispersion equation for the SP instability is a quadratic equation for frequency. The first-step approximation for solution of the dispersion equation, giving the SP-spectrum of frequency, corresponds to the mirror boundary case, when the electron beam propagates above a plane metal surface (mirror). It was found that the conditions for both the Thompson and the Raman regimes of excitation do not depend on beam current and depend on the height of the beam above the grating surface. The growth rate of the instability in both cases is proportional to the square root of the electron beam current. No feedback is needed to provide the coherent emission. [ABSTRACT FROM AUTHOR]

We have studied a time response of electromagnetically induced transparency (EIT) in a rubidium vapor to a rapid variation of optical phase. We have observed a very fast growth of the absorption when the phase of the optical field has been abruptly changed, followed by a slow return to the level of steady-state absorption. The recovery time decreases with increasing optical power. A simple theoretical analysis shows that under our experimental conditions the low power limit of the recovery time is determined by the ground relaxation time. In our case it is defined by a time-of-flight of rubidium atoms through laser beam. The obtained value of the ground state relaxation time is in a good agreement with result of direct measurements by 'relaxation in the dark' method. Our technique based on phase dynamics in EIT can be used for investigation of the ground state relaxation and the fast control of EIT. [ABSTRACT FROM AUTHOR]

We have studied phase dynamics in EIT in a dense rubidium vapor. We have observed a very fast growth of the absorption when the phase of the optical field was abruptly changed, followed by a slow return to the steady state absorption. Then the transmission was slowly restored to stationary magnitude. The recovery time is on the order of the transit time of the atom flying through the laser beam and decreases with increasing optical power. The fast variation of the transparency is proportional to the phase deviation. The obtained result can be used for the fast control of EIT, for example, in an optical switch. [ABSTRACT FROM AUTHOR]

Robust control of atomic coherence and population transfer among Zeeman sublevels in the ground states of rubidium atom is investigated using adiabatic rapid passage in a nanosecond time scale, which is smaller than the lifetime of first excited Rb. It is shown that a slight change in the pump pulse time delay relative to the Stokes pulse leads to a significant modification of atomic coherence and population transfer, consequently having remarkable impacts on the generation of coherent anti-Stokes Raman scattering (CARS) signal and probe pulse absorption. This coherent control of quantum state and population is presented by numerical simulations based on self-consistent set of density matrix equations and Maxwell equations as well as experimental demonstration in rubidium atom with different atomic densities. Experimental observations are in good agreement with numerical calculations. [ABSTRACT FROM AUTHOR]

We study both theoretically and experimentally three-photon electromagnetically induced transparency and electromagnetically induced absorption resonances in inhomogeneously broadened [sup 85]Rb atomic vapour driven by probe and drive laser radiations. We observe narrow Doppler-free absorption as well as transmission resonances for the probe field when the driving laser field is redshifted from the D[sub 1] or D[sub 2] lines of [sup 85]Rb; the frequency difference between the drive and probe fields is equal to the hyperfine splitting of the ground state of the atoms, and the probe field is tuned to the centre of the Doppler broadened atomic transition. We theoretically study the spectroscopic effect in both homogeneously and inhomogeneously broadened media. Our numerical simulations are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]