A cold-atom random laser

Abstract

Conventional lasers make use of optical cavities to provide feedback to gain media. Conversely, mirrorless lasers can be built by using disordered structures to induce multiple scattering, which increases the effective path length in the gain medium and thus provides the necessary feedback. These so-called random lasers potentially offer a new and simple mean to address applications such as lighting. To date, they are all based on condensed-matter media. Interestingly, light or microwave amplification by stimulated emission occurs also naturally in stellar gases and planetary atmospheres. The possibility of additional scattering-induced feedback (that is, random lasing) has been discussed and could explain unusual properties of some space masers. Here, we report the experimental observation of random lasing in a controlled, cold atomic vapour, taking advantage of Raman gain. By tuning the gain frequency in the vicinity of a scattering resonance, we observe an enhancement of the light emission of the cloud due to random lasing. The unique possibility to both control the experimental parameters and to model the microscopic response of our system provides an ideal test bench for better understanding natural lasing sources, in particular the role of resonant scattering feedback in astrophysical lasers

Radiation trapping in a dense cold Rydberg gas

“…Multiple scattering plays a key role in laser cooling, where it limits the phase-space density of the magneto-optical trap (MOT) [1]. The reduction in Doppler broadening also facilitates studies of effects such as coherent backscattering [2], weak localization [3,4], and random lasing [5]. More recent experiments have probed coherent collective effects in free induction decay [6].…”

Recent advances in fundamentals and applications of random fiber lasers

“…The phenomenon of random lasing was first observed by Ambartsumyan et al [17], who replaced one of the mirrors of a ruby laser with a diffusive surface, giving rise to incoherent feedback. Since then, random lasing has been realized in several configurations-colloidal solutions [18], powdered laser crystals [19], zinc oxide powders [20], and even in biological tissues [21] and cold atoms [22]. A comprehensive review of the field in general is beyond the scope of the current work, and the reader is referred to excellent reviews of the field by Cao et al [23,24] and citations therein.…”

Cold and Hot Atomic Vapors: A Testbed for Astrophysics?

“…The model is based on the OBEs with a supplementary incoherent scattering term due to the |2⟩ → |1 ′ ⟩ transition. 73,118 Note that our model neglects the Zeeman degeneracy and thus cannot use the correct relative weight of the different lines. It is thus not precise enough for quantitative predictions.…”

“…Our observations are in qualitative agreement with an ab initio model based on Letokhov's threshold. 73 There are however quantitative discrepancies. In particular, the measured threshold is lower than the predicted one.…”