ABSTRACT
Stand-off magnetometry allows measuring magnetic field at a distance, and can be employed in geophysical research, hazardous environment monitoring, and security applications. Stand-off magnetometry based on resonant scattering from atoms or molecules is often limited by the scarce amounts of detected light. The situation would be dramatically improved if the light emitted by excited atoms were to propagate towards the excitation light source in a directional manner. Here, we demonstrate that this is possible by means of mirrorless lasing. In a tabletop experiment, we detect free-precession signals of ground-state sodium spins under the influence of an external magnetic field by measuring backward-directed light. This method enables scalar magnetometry in the Earth field range, that can be extended to long-range remote sensing.
ABSTRACT
Temporal spiking of directional infrared and ultraviolet cooperative emission from sodium vapors excited to the $4D_{5/2}$ level with a continuous-wave resonant laser pump is analyzed. Mirrorless lasing at 2207 and 2338 nm on cascade population-inverted transitions and radiation at 330 nm generated due to four-wave mixing demonstrate a high degree of intensity correlation.
ABSTRACT
We demonstrate backward-directed continuous-wave (cw) emission at 2.21 µm generated on the 4P3/2-4S1/2 population-inverted transition in Na vapors that are two-photon excited with resonant laser light at 589 and 569 nm. Our study of power and atom-number-density threshold characteristics shows that lasing occurs at sub-10 mW total power of the applied laser light. The observed 6 mrad divergence is defined mainly by the aspect ratio of the gain region. We find that mirrorless lasing at 2.21 µm is magnetic field and polarization dependent and this may be useful for remote magnetometry. The presented results could help determine the requirements for obtaining directional return from sodium atoms in the mesosphere.
ABSTRACT
We report on experimentally observed addition, subtraction, and cancellation of orbital angular momentum (OAM) in the process of parametric four-wave mixing that results in frequency up- and down-converted emission in Rb vapor. Specific features of OAM transfer from resonant laser fields with different optical topological charges to the spatially and temporally coherent blue light (CBL) have been considered. We have observed the conservation of OAM in nonlinear wave mixing in a wide range of experimental conditions, including a noncollinear geometry of the applied laser beams, and furthermore, that the CBL accumulates the total OAM of the applied laser light. Spectral and power dependences of vortex and plane wavefront blue light beams have been compared.
ABSTRACT
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 vapors, we analyze 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 µm is the result of a parametric four-wave mixing process involving only one of the two applied laser fields.
ABSTRACT
Directional infrared emission at 1.37 and 5.23 µm is generated in Rb vapors that are stepwise excited by low-power cw resonant light. The radiation at 5.23 µm originating from amplified spontaneous emission on the 5D(5/2)â6P(3/2) transition and wave mixing consists of forward- and backward-directed components with distinctive spectral and spatial properties. Diffraction-limited light at 1.37 µm generated in the copropagating direction only is a product of parametric wave mixing around the 5P(3/2)â5D(5/2)â6P(3/2)â6S(1/2)â5P(3/2) transition loop. This highly nondegenerate mixing process involves one externally applied and two internally generated optical fields. Similarities between wave mixing generated blue and 1.37 µm light are demonstrated.
ABSTRACT
We investigate frequency up-conversion of low power cw resonant radiation in Rb vapour as a function of various experimental parameters. We present evidence that the process of four wave mixing is responsible for unidirectional blue light generation and that the phase matching conditions along a light-induced waveguide determine the direction and divergence of the blue light. Velocity-selective excitation to the 5D level via step-wise and two-photon processes results in a Doppler-free dependence on the frequency detuning of the applied laser fields from the respective dipole-allowed transitions. Possible schemes for ultraviolet generation are discussed.