Laser Beams In Turbulent Atmosphere Research Articles

Intensity fluctuations of reflected wave from distributed particles illuminated by a laser beam in atmospheric turbulence

The intensity fluctuation of the reflected field from a group of discrete particles illuminated by a laser beam in turbulent atmosphere is investigated here. First, the expression of the correlation function of the received intensity is derived by dividing the illuminated space into a number of sub blocks. Then, the log-amplitude covariance function of the reflected waves from two particles at different heights in a turbulent atmosphere is deduced using the Rytov method. The dimensions of the sub blocks are discussed based on the 3D log-amplitude covariance function, and the normalized variance of the received intensity is calculated and discussed based on the sub blocks. Results show that the normalized variance is mainly affected by the cross section area of the illuminated space, whereas the latter is greatly influenced by the position of the received point and the width of the transmitting beam.

Estimation of propagation losses for infrared laser beam in turbulent atmosphere

In present work, the radiation propagation in atmosphere from laser source to the receiver is considered by taking into account deviations of optical beam due to turbulence. The photon flux density on the receiver has been evaluated.

Design and implementation of scintillation index measuring system based on ARM9

Most research on the scintillation index of laser beam in turbulent atmosphere is limited to numerical method. Based on this point, a scintillation index measuring system (SIMS) based on embedded MCU of ARM9 is designed and realized. The hardware circuit was built on the microprocessor S3C2440; and the software system was transplanted the embedded Linux operating system. The scintillation index of laser beam in a real turbulent atmosphere by using the SIMS is experimentally investigated. The SIMS is proved to be an effective and exact real-time system for measuring scintillation index by comparing the results of experimentally investigation and theory simulation.

Research on propagation properties of controllable hollow flat-topped beams in turbulent atmosphere based on ABCD matrix

This paper studies the propagation properties of controllable hollow flat-topped beams (CHFBs) in turbulent atmosphere based on ABCD matrix, sets up a propagation model and obtains an analytical expression for the propagation. With the help of numerical simulation, the propagation properties of CHFBs in different parameters are studied. Results indicate that in turbulent atmosphere, with the increase of propagation distance, the darkness of CHFBs gradually annihilate, and eventually evolve into Gaussian beams. Compared with the propagation properties in free space, the turbulent atmosphere enhances the diffraction effect of CHFBs and reduces the propagation distance for CHFBs to evolve into Gaussian beams. In strong turbulence atmospheric propagation, Airy disk phenomenon will disappear. The study on the propagation properties of CHFBs in turbulence atmosphere by using ABCD matrix is simple and convenient. This method can also be applied to study the propagation properties of other hollow laser beams in turbulent atmosphere.

Propagation of focused vector laser beams in turbulent atmosphere

By adopting a combination of beam coherence-polarization matrix and extended Huygens–Fresnel integral formula, analytical formulae are derived for the average intensity, the degree of polarization and the RMS (Root-Mean-Square) beam width of focused vector laser beams propagating in a turbulent atmosphere, and the propagation of focused vector laser beams is studied in detail. The spreading properties of vector laser beams and fundamental Gaussian beams are studied comparatively. It reveals that the focused vector laser beam evolves into Gaussian profile in shorter distance compared with collimated vector laser beams, and that destroying of polarization structure of focused ones is more severe. The spreading properties of the focused vector laser beams become the same as that of fundamental Gaussian beams faster. The propagation properties of focused vector laser beams are closely related to the parameters of the beam and the structure constant of the atmospheric turbulence. The results can provide useful reference in designing fiber laser system.

Beam propagation analysis of a multi beam FSO system with partially flat-topped laser beams in turbulent atmosphere

In this paper, the propagation properties of partially coherent flat-topped (PCFT) laser beams in multi-beam FSO communication links are analyzed. Analytical expressions for the average intensity and beam width of PCFT multi beams are derived based on extended Huygens–Fresnel principle by considering the effects of turbulent atmosphere. Also power in bucket (PIB) is calculated numerically based on analytical expression of average intensity. It is revealed that PCFT multi beams can be converted into a Gaussian beam after sufficiently large propagation distance. It is found that correlation length, order of flatness and beams’ separation distances in the source plane have strong effects on minimum distance required for this conversion as well as beam width and PIB. Obtained results are confirmed and illustrated with numerical examples and resulted graphs.

相干合成光束在湍流大气中的传输

相干合成光束在湍流大气中的传输

湍流大气对相干合成远场光束质量的影响

Propagation of coherent combined laser beams in turbulent atmosphere is numerically studied based on the extended Huygens-Fresnel principle. By choosing beam propagation factor (BPF) and beam quality factor (BQ) to characterize the far-field irradiance distribution properties, the influence of turbulence on far-field coherent combined beam quality is studied in detail. The investigation reveals that with the coherence length decreasing, the irradiance distribution pattern evolves from typical non-Gaussian shape with multiple side-lobes into Gaussian shape which is seen in the incoherent combining case. In weak turbulent atmosphere, the far-field beam quality suffers less when the laser array gets more compact and operates at a longer wavelength. In strong turbulent atmosphere, the far-field beam quality degrades into the incoherent combining case without any relationship with the fill factor and laser wavelength.

Propagation of a cosh-Gaussian beam through an optical system in turbulent atmosphere

The propagation of a cosh-Gaussian beam through an arbitrary ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity at any receiver plane are obtained. As an elementary example, the average intensity and its radius at the image plane of a cosh-Gaussian beam through a thin lens are studied. To show the effects of a lens on the average intensity and the intensity radius of the laser beam in turbulent atmosphere, the properties of a collimated cosh-Gaussian beam and a focused cosh-Gaussian beam for direct propagation in turbulent atmosphere are studied and numerically calculated. The average intensity profiles of a cosh-Gaussian beam through a lens can have a shape similar to that of the initial beam for a longer propagation distance than that of a collimated cosh-Gaussian beam for direct propagation. With the increment in the propagation distance, the average intensity radius at the image plane of a cosh-Gaussian beam through a thin lens will be smaller than that at the focal plane of a focused cosh-Gaussian beam for direct propagation. Meanwhile, the intensity distributions at the image plane of a cosh-Gaussian beam through a lens with different w(0) and Omega(0) are also studied.

Propagation of Hermite-cosh-Gaussian laser beams in turbulent atmosphere

The propagation characteristics of Hermite-cosh-Gaussian (HCG) beams in turbulence are studied. To this end, from a HCG source plane excitation, the average intensity of the receiver plane is developed analytically. This formulation is verified against the existing solution of HCG beams in free space. The results indicate that upon traveling in turbulent atmosphere, the HCG beam will undergo three stages of evolution. Initially, it will preserve the original profile. Then, with source parameters of right choice, this beam will turn into a sine shape if the sum of mode indices is odd, and into a cos shape if the sum of mode indices is even. Eventually however, HCG originated beam will become a pure Gassian beam. The dependence of these stages on source and propagation conditions is investigated.