Photon echo under superradiance

The dynamics of optical coherence and phase memory in three-level medium in conditions of superradiance pulse emission is considered. In the case of coherent excitation of the upper level in three-level system of lambda configuration it is shown that the superradiance eliminates optical coherence on the adjacent transitions of excitation and superradiance emission and induces optical coherence on the remain transition. This, in turn, makes it possible to observe new effects of photon-echo, simple example of which is described in the present Letter.     

Fluctuation in superradiance

The fluctuation of the intensity of superradiant pulse is calculated by applying a general asymptotic evaluation method of quantal macrovariables to a superradiant master equation. It is shown that the fluctuation of superradiant intensity is proportional to the cube of the number of the relevant atoms. The time-dependence of the proportional coefficient has been evaluated explicitly. It is predicted that there occurs an enhancement of fluctuation of superradiant intensity at an intermediate time. The intensity and fluctuation of higher order are also calculated. General expressions of expansion coefficients of a generating function are also given rigorously.     

Temperature dependence of superradiance intensity

Using the idea of exchange interaction in a system of two-level atoms participating in a superradiance process, we derive from first principles the superradiance Hamiltonian of such a system, which is found to be analogous to the Heisenberg Hamiltonian. We consistently calculate the coupling constant of the interaction that leads to the emergence of a superradiance state in the system. We also predict the existence of isospin excitations in the superradiance state, whose presence reduces the intensity of the corresponding superradiance pulse. Finally, we calculate the temperature dependence of the intensity of the superradiance pulse and find it be analogous to the Bloch T ^3/2-law for spin systems. Zh. éksp. Teor. Fiz. 116, 1148–1160 (October 1999)     

Induced superradiance in activated crystals

The observation of superradiance in activated crystals induced by propagation of a short coherent pulse through an inverted sample is proposed. The theoretical estimation of the induced superradiance in Nd: YAG is given.     

Optical superradiance in solids

The characteristic features of theoretically describing and experimentally observing superradiance in a diphenyl crystal containing pyrene are discussed together with the possibility of using optical superradiance in crystals as a method for investigating relaxation processes which involve the participation of lattice and pseudolocalized phonons. The possibilities of this method are compared with those of other coherent spectroscopic methods.Scientific-Research Institute of Special Secondary Education, Kazan. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 86–93, July, 1993.     

Equilibrium superradiance in a Bose gas

A model of free₄He atoms interacting with radiation exhibits an equilibrium phase transition in which the atomic ground-state Bose condensation is coupled to condensations of virtual photons and virtually excited atoms of the same macroscopic wavelength. The condensed phase has a twofold polarization degeneracy. It is suggested that this might furnish a mechanism for a discrete symmetry-related phase degeneracy of superfluid liquid⁴He required to explain the transition according to Tisza's generalized Gibbsian thermodynamics. A more realistic model would require inclusion of repulsive interactions.Supported in part by the National Science Foundation, Grant DMR76-17467.     

Stochastic structure of superradiance pulses

We have made a theoretical study of the statistics of superradiant pulses excited by pumping pulses. We describe experiments on the superradiance of a dye (Rhodamine 6G) that confirm the theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 4, pp. 73–78, April, 1976.     

Generalized Fokker-Planck equation in superradiance theory

An alternative projector technique approach to the Bonifacio-Schwendimann-Haake model of superradiance is presented. A bilinear master equation for the probability distributions of photon number and atomic excitation is derived. In the case of very large numbers of atoms we end up with a generalized Fokker-Planck equation for atoms.     

Experimental observation of cyclotron superradiance

Intense (several hundreds of kilowatts) subnanosecond coherent microwave radiation — cyclotron superradiance of an electron swarm moving in a uniform magnetic field — was recorded. The maximum power of the radiation was observed under group synchronization conditions, when the translational velocity of the swarm is equal to the group velocity of the waves in the waveguide channel. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 322–325 (10 March 1996)     

On the theory of vibronic superradiance

The Dicke superradiance on vibronic transitions of impurity crystals is considered. It is shown that parameters of the superradiance (duration and intensity of the superradiance pulse and delay times) on each vibronic transition depend on the strength of coupling of electronic states with the intramolecular impurity vibration (responsible for the vibronic structure of the optical spectrum in the form of vibrational replicas of the pure electronic line) and on the crystal temperature through the Debye-Waller factor of the lattice vibrations. Theoretical estimates of the ratios of the time delays, as well as of the superradiance pulse intensities for different vibronic transitions well agree with the results of experimental observations of two-color superradiance in the polar dielectric KCl:O ₂ ^? . In addition, the theory describes qualitatively correctly the critical temperature dependence of the superradiance effect.     

Polarization of radiation under superradiance conditions

A theoretical study is made of the polarization properties of superradiance emitted by gases in a high-current longitudinal discharge. It is shown that the Zeeman effect in the discharge current makes the radiation at the periphery of a light beam totally polarized. Formulas are derived for relating the degree of polarization of a light beam with the dependences of the gain profile on the frequency and on the transverse coordinate. An analysis is made of the influence of diffraction on the polarization properties of a light beam and the anisotropic waveguide modes are found. A calculation is made of the distribution of the intensity of the optical field when radiation is generated between crossed Polaroids at the exit end of the discharge tube.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 51–56, May, 1980.The authors are grateful to A. I. Odintsov and V. P. Yakunin for frequent discussions.     

The counter-rotating terms in the superradiance

Summary It is pointed out that the counter-rotating terms play an important role in the superradiance of the first kind, in which the atomic system is initially in an uncorrelated state with maximal dipole moment. If the counter-rotating terms are added to the master equation for the Dicke model derived by Agarwal and Bonifacioet al., the numerical solutions for the atomic-population inversion and radiation rate show strong damped oscillations (damped recurrence effects) in their time behaviour. A new limiting relation for the cut-off frequency, which depends on the number of atoms, is also obtained for the treated model.

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Riassunto Si evidenzia che i termini controrotanti svolgono un importante ruolo nella superradianza del primo tipo, in cui il sistema atomico è inizialmente in uno stato incorrelato con impulso dipolare massimo. Se i termini controrotanti sono aggiunti all’equazione principale per il modello di Dicke derivato da Agarwal e Bonifacioet al., le soluzioni numeriche per l’inversione di popolazione atomica e il valore di radiazione mostrano forti oscillazioni smorzate (effetti di ricorrenza smorzati) nel loro comportamento nel tempo. Si ottiene anche una nuova relazione per la frequenza di taglio per il modello trattato che dipende dal numero di atomi.

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Резюме Отмечается, что члены с противоположным вращением играют важную роль в суперсветимости первого рода, где атомная система первоначально находится в некоррелированном состоянии с максимальным дипольным моментом. Если члены с противоположным вращением добавляются в ?управляющие? уравнение для модели Дикка, которое было получено Агарвалом, Ъонифачио и др., то численные решения для инверсии атомной заселенности и интенсивности излучения обнаруживают сильные затухающиее осцилляции (затухаюцие рекуррентные эффекты), в их временном поведении. Для рассматриваемой модели получено новое предельное соотношение для частоты обрезания, которая зависит от числа атомов.

     

X波段重复频率GW级超辐射相对论返波管

运用超辐射机理,通过粒子模拟设计了X波段超辐射相对论返波管,并在小型Tesla脉冲源平台上开展了实验研究。通过空间功率积分和直接对辐射微波时域波形的分析得到实验结果：在束压350 kV、束流4.8 kA、脉宽3.1 ns、引导磁场2.2 T条件下,产生的微波辐射功率1.4 GW,中心频率9.36 GHz,脉宽500~700 ps,辐射模式为TE11,能在重复频率100 Hz下稳定运行。功率转换效率超过80%。实验结果与粒子模拟结果比较吻合,成功实现了在短脉冲条件下产生重复频率、亚纳秒脉宽、GW级微波辐射。     

The single photon superradiance from the eigenmode analysis

Using the eigenmode analysis of the scalar photon theory, I compute the probability of the atoms remaining excited and the probability for the atoms remaining in the initial quantum state of a system of two-level atoms cloud in a sphere initially prepared to radiate in the forward direction, i.e., the single photon superradiance problem. The convergence in the results obtained for increasingly larger radii for the sphere suggests that the asymptotic limits for these quantities are obtained for a sphere with a radius equal to six times the resonant wavelength. I predict the maximal value of the probability of secondary excited states from large spheres at 17.1%.     

Phonon superradiance and phonon laser effect in nanomagnets

We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.     

Entanglement and the phase transition in single-mode superradiance

We consider the entanglement properties of the quantum phase transition in the single-mode superradiance model, involving the interaction of a boson mode and an ensemble of atoms. For an infinite size system, the atom-field entanglement diverges logarithmically with the correlation length exponent. Using a continuous variable representation, we compare this to the divergence of the entropy in conformal field theories and derive an exact expression for the scaled concurrence and the cusplike nonanalyticity of the momentum squeezing.     

A modified equation for single-mode superradiance kinetics

A new method is proposed for decoupling the chain of quantum equations, which incorporates the fluctuations in the population difference between levels in the atoms near the maximum in the superradiance intensity. A new system of equations is derived that describes a broader and more unsymmetrical superradiance pulse than does the results of [1–4]. The new solutions improve the agreement between theory and experiment [5].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 27, No. 1, pp. 28–33, January, 1984.