An analytical expression of an Airy beam propagating in a strongly nonlocal nonlinear media is derived. The analytical expressions of the corresponding characteristic parameters for the Airy beam, such as the centre of gravity, the effective beam size, the curvature radius, the kurtosis parameter, and the linear momentum, have also been presented, respectively. The normalized intensity distribution and these characteristic parameters are pictorially demonstrated in the strongly nonlocal nonlinear media, respectively. It shows all the characteristic parameters versus the axial propagation distance are periodic. The period of the linear momentum versus the axial propagation distance isThe period of other characteristic parameters and the normalized intensity isThe periodic behavior of the Airy beam in the strongly nonlocal nonlinear media has promising application in optical switch and optical micromanipulation.
Standoff detections of explosives using quantum cascade lasers (QCLs) and the photoacoustic (PA) technique were studied. In our experiment, a mid-infrared QCL with emission wavelength near 7.35 μm was used as a laser source. Direct standoff PA detection of trinitrotoluene (TNT) was achieved using an ultrasensitive microphone. The QCL output light was focused on explosive samples in powder form. PA signals were generated and detected directly by an ultrasensitive low-noise microphone with 1 in. diameter. A detection distance up to 8 in. was obtained using the microphone alone. With increasing detection distance, the measured PA signal not only decayed in amplitude but also presented phase delays, which clearly verified the source location. To further increase the detection distance, a parabolic sound reflector was used for effective sound collection. With the help of the sound reflector, standoff PA detection of TNT with distance of 8 ft was demonstrated.
Abstract-The propagation properties of a Lorentz-Gauss vortex beam in a turbulent atmosphere are investigated. Based on the extended Huygens-Fresnel integral, the Hermite-Gaussian expansion of a Lorentz function, etc., analytical expressions of the average intensity, effective beam size, and kurtosis parameter of a LorentzGauss vortex beam are derived in the turbulent atmosphere. The spreading properties of a Lorentz-Gauss vortex beam in the turbulent atmosphere are numerically calculated and analyzed. The influences of the beam parameters on the propagation of a Lorentz-Gauss vortex beam in the turbulent atmosphere are examined in details. Upon propagation in the turbulent atmosphere, the vale in the normalized intensity distribution of a Lorentz-Gauss vortex beam gradually rises. The rising speed of the vale is opposite to the spreading of the beam spot. When the propagation distance reaches to a certain value, the Lorentz-Gauss vortex beam in the turbulent atmosphere becomes a flattened beam spot. When the propagation distance is large enough, the beam spot of the Lorentz-Gauss vortex beam tends to be a Gaussian-like distribution. This research is beneficial to optical communications and remote sensing that are involved in the single mode diode laser devices.
Based on the vectorial Rayleigh-Sommerfeld integral formulae, the analytical expression of a general Lorentz-Gauss vortex beam with an arbitrary topological charge is derived in free space. By using the analytical expressions of the electromagnetic field beyond the paraxial approximation, the orbital angular momentum density of a general Lorentz-Gauss vortex beam can be calculated. The effects of the linearly polarized angle and the topological charge on the three components of the orbital angular momentum density are investigated in the reference plane. The two transversal components of the orbital angular momentum are composed of two lobes with the same areas and opposite signs. The longitudinal component of the orbital angular momentum density is composed of four lobes with the same areas. The sign of the orbital angular momentum density in a pair of lobes is positive, and that of the orbital angular momentum density in the other pair of lobes is negative. Moreover, the negative magnitude of the orbital angular momentum density is larger than the positive magnitude of the orbital angular momentum density. The linearly polarized angle affects not only the shape and the location of the lobes, but also the magnitude of the three components of the orbital angular momentum density. With increasing the topological charge, the distribution of the orbital angular momentum density expands, the magnitude of the orbital angular momentum density increases, and the shape of the lobe also slightly changes.
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