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Random Lasing in an Inhomogeneous and Disordered System of Cold Atoms  [PDF]
L. V. Gerasimov,D. V. Kupriyanov,M. D. Havey
Physics , 2015, DOI: 10.1134/S0030400X1509009X
Abstract: We consider light trapping in an amplifying medium consisting of cold alkali-metal atoms; the atomic gas plays a dual role as a scattering and as a gain medium. We perform Monte-Carlo simulations for the combined processes. In some configurations of the inhomogeneous distribution this leads to a point of instability behavior and a signature of random lasing in a cold atomic gas.
Optical parametric oscillation with distributed feedback in cold atoms  [PDF]
Alexander Schilke,Claus Zimmermann,Philippe W. Courteille,William Guerin
Physics , 2011, DOI: 10.1038/nphoton.2011.320
Abstract: There is currently a strong interest in mirrorless lasing systems, in which the electromagnetic feedback is provided either by disorder (multiple scattering in the gain medium) or by order (multiple Bragg reflection). These mechanisms correspond, respectively, to random lasers and photonic crystal lasers. The crossover regime between order and disorder, or correlated disorder, has also been investigated with some success. Here, we report one-dimensional photonic-crystal lasing (that is, distributed feedback lasing) with a cold atom cloud that simultaneously provides both gain and feedback. The atoms are trapped in a one-dimensional lattice, producing a density modulation that creates a strong Bragg reflection with a small angle of incidence. Pumping the atoms with auxiliary beams induces four-wave mixing, which provides parametric gain. The combination of both ingredients generates a mirrorless parametric oscillation with a conical output emission, the apex angle of which is tunable with the lattice periodicity.
A Cold-Strontium Laser in the Superradiant Crossover Regime  [PDF]
Matthew A. Norcia,James K. Thompson
Physics , 2015,
Abstract: Recent proposals suggest that lasers based on narrow dipole-forbidden transitions in cold alkaline earth atoms could achieve linewidths that are orders of magnitude smaller than linewidths of any existing lasers. Here, we demonstrate a laser based on the 7.5 kHz linewidth dipole forbidden $^3 $P$_1$ to $^1 $S$_0$ transition in laser-cooled and tightly confined $^{88}$Sr. We can operate this laser in the bad-cavity regime, where coherence is primarily stored in the atoms, or continuously tune to the more conventional good-cavity regime, where coherence is primarily stored in the light field. We show that the cold-atom gain medium can be repumped to achieve quasi steady-state lasing, and demonstrate up to an order of magnitude suppression in the sensitivity of laser frequency to changes in cavity length, the primary limitation for the most frequency stable lasers today.
Electron shelving induced lasing in cold bosonic atoms in optical lattice  [PDF]
Aranyabhuti Bhattacherjee
Physics , 2004,
Abstract: We calculate the absorption spectrum of cold three level Helium atoms in lambda configuration in an optical lattice.Our results show the possibilty of lasing at certain points on the optical lattice which are capable of rendering one of the transitions metastable as compared to the other. A coherent control over the stimulated emission is possible using an axial magnetic field.
Euclidean matrix theory of random lasing in a cloud of cold atoms  [PDF]
A. Goetschy,S. E. Skipetrov
Physics , 2011, DOI: 10.1209/0295-5075/96/34005
Abstract: We develop an ab initio analytic theory of random lasing in an ensemble of atoms that both scatter and amplify light. The theory applies all the way from low to high density of atoms. The properties of the random laser are controlled by an Euclidean matrix with elements equal to the Green's function of the Helmholtz equation between pairs of atoms in the system. Lasing threshold and the intensity of laser emission are calculated in the semiclassical approximation. The results are compared to the outcome of the diffusion theory of random lasing.
Threshold of a random laser based on Raman gain in cold atoms  [PDF]
William Guerin,Nicolas Mercadier,Davide Brivio,Robin Kaiser
Physics , 2009, DOI: 10.1364/OE.17.011236
Abstract: We address the problem of achieving a random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. In this system, the elastic scattering cross-section is related to the complex atomic polarizability. As a consequence, the random laser threshold is expressed as a function of this polarizability, which can be fully determined by spectroscopic measurements. We apply this idea to experimentally evaluate the threshold of a random laser based on Raman gain between non-degenerate Zeeman states and find a critical optical thickness on the order of 200, which is within reach of state-of-the-art cold-atom experiments.
Threshold of a Random Laser with Cold Atoms  [PDF]
Luis S. Froufe-Pérez,William Guerin,Rémi Carminati,Robin Kaiser
Physics , 2008, DOI: 10.1103/PhysRevLett.102.173903
Abstract: We address the problem of achieving an optical random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. The lasing threshold can be defined using the on-resonance optical thickness b0 as a single critical parameter. We predict the threshold quantitatively, as well as power and frequency of the emitted light, using two different light transport models and the atomic polarizability of a strongly-pumped two-level atom. We find a critical b0 on the order of 300, which is within reach of state-of-the-art cold-atom experiments. Interestingly, we find that random lasing can already occur in a regime of relatively low scattering.
Towards a random laser with cold atoms  [PDF]
William Guerin,Nicolas Mercadier,Franck Michaud,Davide Brivio,Luis S. Froufe-Pérez,Rémi Carminati,Vitalie Eremeev,Arthur Goetschy,Sergey E. Skipetrov,Robin Kaiser
Physics , 2009, DOI: 10.1088/2040-8978/12/2/024002
Abstract: Atoms can scatter light and they can also amplify it by stimulated emission. From this simple starting point, we examine the possibility of realizing a random laser in a cloud of laser-cooled atoms. The answer is not obvious as both processes (elastic scattering and stimulated emission) seem to exclude one another: pumping atoms to make them behave as amplifier reduces drastically their scattering cross-section. However, we show that even the simplest atom model allows the efficient combination of gain and scattering. Moreover, supplementary degrees of freedom that atoms offer allow the use of several gain mechanisms, depending on the pumping scheme. We thus first study these different gain mechanisms and show experimentally that they can induce (standard) lasing. We then present how the constraint of combining scattering and gain can be quantified, which leads to an evaluation of the random laser threshold. The results are promising and we draw some prospects for a practical realization of a random laser with cold atoms.
Lasing and cooling in a hot cavity  [PDF]
Thomas Salzburger Helmut Ritsch
Physics , 2006, DOI: 10.1103/PhysRevA.74.033806
Abstract: We present a microscopic laser model for many atoms coupled to a single cavity mode, including the light forces resulting from atom-field momentum exchange. Within a semiclassical description, we solve the equations for atomic motion and internal dynamics to obtain analytic expressions for the optical potential and friction force seen by each atom. When optical gain is maximum at frequencies where the light field extracts kinetic energy from the atomic motion, the dynamics combines optical lasing and motional cooling. From the corresponding momentum diffusion coefficient we predict sub-Doppler temperatures in the stationary state. This generalizes the theory of cavity enhanced laser cooling to active cavity systems. We identify the gain induced reduction of the effective resonator linewidth as key origin for the faster cooling and lower temperatures, which implys that a bad cavity with a gain medium can replace a high-Q cavity. In addition, this shows the importance of light forces for gas lasers in the low-temperature limit, where atoms can arrange in a periodic pattern maximizing gain and counteracting spatial hole burning. Ultimately, in the low temperature limit, such a setup should allow to combine optical lasing and atom lasing in single device.
Observation of lasing without inversion in a hot rubidium vapor under electromagnetically-induced transparency conditions  [PDF]
Haibin Wu,Min Xiao,J. Gea-Banacloche
Physics , 2008, DOI: 10.1103/PhysRevA.78.041802
Abstract: We have observed CW lasing without inversion in a gas of hot rubidium atoms in an optical cavity under conditions of electromagnetically-induced transparency (EIT). The medium is pumped coherently and resonantly by a single ``coupling'' beam which also produces EIT in the lasing transition. The steady-state intensity exhibits thresholds as a function of the atomic density and the strength of the coupling beam. A theoretical model for an effective three-level lambda system indicates that gain without inversion is possible in this system if the two ground states are coupled by depolarizing collisions, and if the decay branching ratios meet certain conditions.
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