Observation of superfluorescent emissions from laser-cooled atoms

Abstract

We study superfluorescence ͑SF͒ from spherical and cigar-shaped clouds of laser-cooled Rubidium atoms from the 5D 5/2 level through the 6P 3/2 level to the 5S 1/2 ground level. The atomic system is initially excited to the 5D 5/2 level from the ground state via two-photon excitation through the intermediate 5P 3/2 level. The fluorescence on the 6P-5S transition at 420 nm is recorded using time-resolved measurements. The time delays of the observed SF emission peaks typically scale as ϳN −1 , where N is the atom number, and are much smaller than the time delay expected for uncorrelated cascade fluorescence. Since N is significantly smaller than the threshold number for SF on the 420 nm transition, and larger than the threshold number for the 5D-6P transition at 5.2 m, our observations suggest that the 420 nm SF emission is triggered by rapid deexcitation of the 5D to the 6P level via SF at 5.2 m. The observed SF time delays for 420 nm emission agree with SF time-delay estimates for the 5.2 m transition. For spherical clouds, the SF is isotropic. For cigar-shaped clouds, the SF is highly anisotropic. Along the long axis of cigar-shaped atom clouds, SF and incoherent cascade fluorescence produce temporally well-resolved peaks in the detected signal. In this case, the SF component of the signal is highly concentrated along a direction in between the directions of the two almost parallel excitation beams. The observed SF intensities scale as N, suggesting that the 5D level is regeneratively pumped during the SF decay.

Observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses

“…The experimental observation and theoretical description of the yoked SF with omnidirectional character (in rubidium vapor) were accomplished by Lvovsky et al [18,19]. Recently, Paradis et al obtained striking results while observing the yoked SF in laser-cooled rubidium atoms [20].…”

“…The same atomic configuration and associated radiation processes were recently considered by Lvovsky et al [18,19] and Paradis et al [20]. The delay between the input pulse and SF as a function of the number density of the atoms was presented by Lvovsky [19] by varying input pulse energy or the temperature of the vapor, and by Paradis [20] by loading different numbers of atoms into the magnetooptical trap.…”

“…The delay between the input pulse and SF as a function of the number density of the atoms was presented by Lvovsky [19] by varying input pulse energy or the temperature of the vapor, and by Paradis [20] by loading different numbers of atoms into the magnetooptical trap.…”

Second-order coherence of superradiance from a Bose-Einstein condensate

“…and, as a result, a complex nomenclature has evolved including the terms superradiance, superfluorescence, amplified spontaneous emission, mirrorless lasing, and random lasing [2, 4,[6][7][8][9], the distinctions among which we will not attempt to summarize here. The problem has recently seen renewed interest in the field of cold atoms [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. This is partly because cold atoms provide a reproducible, easily characterized ensemble in which Doppler broadening effects are small and relaxation is generally limited to spontaneous emission.…”

Stimulated emission of an atomic system under coherent excitation

“…Later, these effects were detected in cesium atomic beams [2], as well as in ensembles of rubidium atoms [3,4]. The ideas of Dicke were subsequently developed in numerous publications (see for instance [5,6]), which included mostly bi-level systems with different ways of population inversion, possibly leading to superradiance -high intensity pulses, followed by a certain delay in relation to the inverse state formation time.…”