Vector coherence initiation of multi-level superfluorescence

An SU(n) coherent state representation is developed for the theory of multi-level cooperative spontaneous emission. A general Fokker-Planck equation is derived, whose characteristics are equivalent to the semiclassical equations for large numbers of atoms. The characteristics equations have non-classical initial values described by a vector coherence probability distribution. The theory can be used for the multilevel case with coherent pumping, to calculate the effects of pump interactions.     

Theory of superfluorescence beats

A theory of superfluorescence beats is developed which takes into account both quantum fluctuations and a finite sample size. Analytic results for the radiated intensity in the linear regime are presented. The intensity carries a modulation at the beat frequency.     

Cooperative superfluorescence in nanoclusters

The features of superfluorescence (SF) in nanoclusters, which consist of a few neighboring particles interacting with each other by exchange or/and electrostatic forces, are investigated theoretically. It is shown that there are two types of cooperatively SF depending on the ratio between the linear size of a nanocluster and the cooperative interaction range. Experiments on cooperative luminescence in Ytterbium-doped silica fibers are analyzed. It is shown that the intensity of cooperative SF in such a system should be proportional to the fourth degree of Ytterbium concentration.     

Transverse effects in superfluorescence

We demonstrate that off-axial emission can be responsible for the pulse envelope ringing, transverse effects, and large shot-to-shot pulse shape fluctuations observed in recent superfluorescence experiments.     

Statistical properties of oscillatory superfluorescence

We investigate the statistical properties of oscillatory superfluorescence by extending the Haake-Glauber treatment of pure superfluorescence to the case in which the field variables cannot be adiabatically eliminated. The numerical results are compared with those previously found by different approaches.The main differences are: i) a sensible lowering of the minima of the mean value of the field intensity; ii) a marked enhancement of the fluctuations of both the field and atomic variables and of the atom-field correlations.     

Statistics of composed pulses in superfluorescence

The statistics of superfluorescence pulses, which are formed by the superposition of N independently generated ones, may be derived from the single-pulse statistics. Three possibilities are presented and discussed. An intuitive interpretation of some recent results in three-dimensional superfluorescence becomes obvious.     

Visible superfluorescence from optically pumped europium atoms

We have observed superfluorescence (SF) on five atomic transitions at visible wavelengths 633.58, 635.00, 640.09, 640.61 and 736.22 nm in Doppler broadened gas of europium (Eu) atom. The nanosecond SF pulses were observed by longitudinally pumping Eu vapor column with a pulsed dye laser to upper states 4f⁶5d6s², ⁸D_7/2at 346.79 nm and 4f⁷5d6p, ¹⁰F_5/2at 348.73 nm from the ground state 4f⁷6s², ⁸S_7/2. High optical conversion efficiency ≈10% was measured for these SF transitions. Our experiment deals with the large sample multilevel SF in the regime where the length of the excited column L is greater than the maximum value of the Arecchi-Courtens length (L_c). The observed variation of SF peak intensity (I_fl) and time delay for SF evolution (τ_D) with number of atoms in the excited state (N) resemble theoretically predicted SF scaling laws for transverse excitation, namely I_fl∝N and t_D μ 1/?N\tau_D \propto 1/{\sqrt N} although the experimental condition is similar to the swept excitation. This could be due to the Rabi frequency associated with the pump transition which is comparable to the SF delay time precluding the initiation of SF at different times along the sample and results in transverse (instantaneous) excitation. The experimental τ_D values were found to be in agreement with the quantum mechanical calculations describing SF.     

Observation of free-electron-laser-induced collective spontaneous emission (superfluorescence)

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as ρ(2) and the emitted pulse width and delay to scale as ρ(-1), where ρ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75,000 times faster than the spontaneous 1s3p → 1s2s decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.     

染料溶液中微微秒超荧光光谱的动力学研究

本文介绍采用时间分辨的频率上转换法研究染料溶液中微微秒超荧光光谱动力学过程的装置和实验结果.实验研究了超荧光的脉宽压缩,荧光中心波长的位移和增益带宽对泵浦光参量以及染料溶液浓度的依赖关系.     

Quantum fluctuations of superfluorescence delay observed with ultrashort optical excitations

We present an observation of fluctuations in delay times of the yoked-superfluorescence pulses generated in atomic rubidium. The yoked-superfluorescence was induced through two-photon excitation of cascade transitions by ultrashort (∼100 fs) laser pulses. A statistical distribution and fluctuations of delay times were studied as the pump pulse energy varied, effectively changing the number of participating atoms. The standard deviation in the delay-time statistics decreases when the pump power increases. The experimental data support the theoretical model of the quantum fluctuations of superfluorescence.     

Observation of superfluorescence and stimulated emission in Bi I after nonresonant two-photon pumping

We report the observation of superfluorescence and of stimulated emission in the near-infrared at 965.69 nm in atomic Bi. The atoms are prepared in the 6p ²(³ P ₀)7p _3/2 upper state by nonresonant two-photon excitation. The cooperative character of the emission is demonstrated by the delay of the light pulses and their N² dependence upon the atomic density.     

A solution of the sine-Gordon equation with boundary conditions appropriate to oscillating superfluorescence

A procedure is given for solving the sine-Gordon equation with boundary conditions which define the physical problem of superfluorescent emission from an inverted and spatially extended medium. The shape of the leading pulse is calculated. An important new result is a verification and extension of the form of the expression of MacGillivray and Feld and of Skribanowitz, Herman, MacGillivray and Feld for the delay time τ_D in oscillating superfluorescence.     

Angular distribution of superfluorescence energy of drops for the two-photon absorption of nano-and femtosecond laser pulses

Results of investigations into the spectral, energy, and spatial characteristics of rhodamin 6G fluorescence of a liquid drop are presented for the two-photon absorption of nano-and femtosecond laser pulses. It is demonstrated that the characteristics of stimulated radiation from different drop-resonator zones differ significantly, but are of the same type for femto-and nanosecond pumping. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–5, January, 2008.     

Tunable te-CO2 laser-pumped formaldehyde far-infrared lasers: Offsets, assignment, and superfluorescence

Sixty and three absorption transitions in D₂CO and H₂CO, respectively, have produced a number of far infrared laser lines when they are pumped by an etalon-tuned TE-CO₂ laser. Almost all the absorption transitions pumped previously by a free runing TE-CO₂ laser have been efficiently pumped by the etalon tuned CO₂ laser and found to have offset within ±500 MHz from the line-center of the relevant CO₂ pump lines. 22 (1) absorption and 63 (4) emission lines of D₂CO (H₂CO) are assigned. Some of these lines have generated superfluorescence. In paticular, the D₂CO 319-m line pumped by CO₂-9P(32) delivered an output energy of approximately one half that of the well-known D₂O 66-m. It is shown that a large electric dipole moment and an appreciable amount of fractional population in the lower level of the pump transition of this line are responsible to the superfluorescence.