Omnidirectional Superfluorescence

Abstract

A dense sample of atomic Rb vapor excited by a 4 ps laser pulse two-photon resonant with the 5S-5D transition in a large Fresnel number geometry emits a delayed coherent omnidirectional ir pulse on the 5D-6P transition. This superfluorescence emission involves a coherent population transfer to the 6P level and results in simultaneous directional uv emission and coherent population transfer back to the ground 5S state. This uv emission is a manifestation of parametric time-delayed four-wave mixing. For a composite noncollinear, j k 1 j j k 2 j, excitation, the uv radiation pattern is conical and the cone angle depends on the angle between the excitation pulses. [S0031-9007 (99)09254-6] PACS numbers: 42.50.Fx, 42.65.HwAmplified spontaneous emission (ASE) occurs whenever a system is pumped so that there is gain aL . 1 along the sample length L [1]. For sufficiently high gain, aL ¿ 1, the fields developed become so strong that they modify the atomic state populations; the intensity of the emission becomes proportional to the square of the number of cooperating radiators and superfluorescence obtains. Classical superfluorescence experiments were performed in elongated samples which allowed development of two minimally competing superfluorescent modes, forward and backward [2][3][4]. In the present work, the sample is quasispherical and the gain is large in all directions. Now mode competition is significant and might be expected to either preclude the development of superfluorescence altogether or to at least restrict it to a few well isolated modes which would randomly fire from one shot to the next. Nevertheless, we find that superfluorescence develops and it is omnidirectional. This cannot arise from a spherical mode as the sample is large compared to the radiation wavelength. It must be that, in our sample, spontaneously emitted randomly directed photons are amplified and, in the process, generate separate antennas. These are macroscopic antennas (each consisting of a phased array of many oscillating atomic dipoles) which, if sufficiently excited, radiate a coherent burst of radiation in a time much shorter than the fluorescence lifetime T 1 . It is the classic case of radiation damping [5]. Thus, a three-dimensional distribution of randomly phased (with respect to each other) antennas (a kind of pin cushion array), individually directed throughout 4p, is produced and each antenna separately and simultaneously produces a short (compared to T 1 ) coherent burst.We work in Rb vapor and generate a high gain inversion on the 5D-6P transition by applying a short laser pulse two-photon resonant with the 5S-5D transition. This pulse is sufficiently short that (i) no appreciable superfluorescence takes place during its application and (ii) the atoms are left in a coherent superposition of states jS͘ and jD͘. Since the 5P state is not populated by the excitation pulse, both the 5D-6P and the 5D-5P transitions are inverted with the gain on the former dominating completely as it lies in the far infrared while the latter lies...

Collective enhancement and suppression in Bose-Einstein condensates

“…For a large outcoupled fraction, population n k−q and N q is built up in the final states and stimulates further scattering. This collisional amplification is not directional, and is similar to the recently observed optical omnidirectional superfluoresence [24].…”

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

“…A crucial example of cascade cooperative emission, the so-called yoked SF, was first observed in cesium vapor by Brownell et al [17]. 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.…”

Coherence brightened laser source for atmospheric remote sensing

“…Availability of a laserlike light source emitting radiation in a controlled directional fashion, from a point in the sky back toward a detector, should revolutionize remote sensing (8,9). Dogariu et al demonstrated the possibility of remote lasing of atmospheric oxygen by using sub-mJ picosecond UV laser pulses at 226 nm that produce a bright near-infrared (NIR) laser source at 845 nm wavelength using atomic oxygen as the gain medium (10).It has been proposed that a mirrorless laser can be used as a superradiant source where coherence is large, such as a coherence brightened laser (11)(12)(13)(14). This type of superradiance was first demonstrated in optically pumped HF gas (15).…”

“…It has been proposed that a mirrorless laser can be used as a superradiant source where coherence is large, such as a coherence brightened laser (11)(12)(13)(14). This type of superradiance was first demonstrated in optically pumped HF gas (15).…”