Directional infrared emission resulting from cascade population inversion and four-wave mixing in Rb vapours

Directional infrared emission at 1367 and 5230 nm is generated in Rb vapours that are step-wise excited by low-power resonant light. The mid-infrared radiation originating from amplified spontaneous emission on the 5D-6P transition consists of forward- and backward-directed components with distinctive spectral and spatial properties. Diffraction limited near-infrared light at 1367 nm generated in the co-propagating direction only is a product of parametric wave mixing around the 5P-5D-6P-6S-5P transition loop. This highly non-degenerate mixing process involves one externally applied and two internally generated optical fields. Similarities between wave mixing generated blue and near-IR light are demonstrated.Comment: 4 pages, 5 figure

Comparison of collimated blue-light generation in Rb-85 atoms via the D-1 and D-2 lines

We experimentally and theoretically studied the characteristics of the collimated blue light (CBL) produced in Rb-85 vapor by two resonant laser fields exciting atoms into the 5D(3/2) state, using either the 5P(1/2) or the 5P(3/2) intermediate state. We compared the CBL output at different values of frequency detunings, powers, and polarizations of the pump lasers in these two cases and confirmed the observed trends using a simple theoretical model. We found that in general the CBL yield was higher for the the D-1 excitation scheme compared to the D-2 excitation scheme under similar conditions. We also demonstrated the importance of the repump laser, preventing the accumulation of atomic population in the uncoupled hyperfine ground state, which resulted in nearly an order of magnitude increase in CBL power output. One interesting finding was the existence of the optimal power ratios between the two pump lasers, leading to the maximum blue- light power, observed both in the experiment and in the calculations. (C) 2018 Optical Society of Americ

Optical parametric oscillation with distributed feedback in cold atoms

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

Distinguishing nonlinear processes in atomic media via orbital angular momentum transfer

We suggest a technique based on the transfer of topological charge from applied laser radiation to directional and coherent optical fields generated in ladder-type excited atomic media to identify the major processes responsible for their appearance. As an illustration, in Rb vapours we analyse transverse intensity and phase profiles of the forward-directed collimated blue and near-IR light using self-interference and astigmatic transformation techniques when either or both of two resonant laser beams carry orbital angular momentum. Our observations unambiguously demonstrate that emission at 1.37 {\mu}m is the result of a parametric four-wave mixing process involving only one of the two applied laser fields.Comment: 4 pages, 5 figure

Remote Detection Optical Magnetometry

Sensitive magnetometers have been applied in a wide range of research fields, including geophysical exploration, bio-magnetic field detection, ultralow-field nuclear magnetic resonance, etc. Commonly, magnetometers are directly placed at the position where the magnetic field is to be measured. However, in some situations, for example in near space or harsh environments, near nuclear reactors or particle accelerators, it is hard to place a magnetometer directly there. If the magnetic field can be detected remotely, i.e., via stand-off detection, this problem can be solved. As optical magnetometers are based on optical readout, they are naturally promising for stand-off detection. We review various approaches to optical stand-off magnetometry proposed and developed over the years, culminating in recent results on measuring magnetic fields in the mesosphere using laser guide stars, magnetometry with mirrorless-lasing readout, and proposals for satellite-assisted interrogation of atmospheric sodium.Comment: 68 pages, 19 figure