An experimental scheme based on interferometry is designed to measure the orbital angular momentum spectrum of vortex beam perturbed by turbulence. The orbital angular momentum spectrum of vortex beam can be calculated by using four light intensity images. The laser beam is modulated by a spatial light modulator to obtain a vortex beam, and then passes through another spatial light modulator loaded with a turbulent phase perturbation hologram to interfere with the reference beam. The orbital angular momentum spectrum of the vortex beam can be obtained by making use of two interference patterns and the intensity patterns of the vortex beam and the reference beam. The results show that the experimental scheme can measure the orbital angular momentum spectrum of the vortex beam affected by turbulence.
In order to study the anti-turbulence performance of the perfect vortex beam which carrying Orbital angular momentum(OAM), the average intensity distribution, beam spreading and scintillation characteristics of the perfect vortex beam propagating in atmospheric turbulence are simulated based on the multi-phase screen method by making use of the Von Karman spectrum. The impacts of beam parameters (OAM number, wavelength,) and atmospheric turbulence parameters (inner scale, outer scale) on the beam spreading and scintillation of perfect vortex beams are investigated. The results show that the beam parameters can be adjusted to reduce the scintillation and beam spreading effects caused by atmospheric turbulence. Perfect vortex beams with smaller OAM numbers and larger wavelengths have better resistance to turbulence. The smaller the outer scale and the larger the inner scale of the atmospheric turbulence, the better propagation performance of perfect vortex beam. The research of this paper provides an important reference for optimizing the optical communication performance of perfect vortex beams in atmospheric turbulence.
When the aircraft is flying in the air at high speed, it will compress the surrounding air to form a shock wave layer on the front of aircraft, and the shock wave will gradually turn into turbulence as the distance from the front of the aircraft increases. When the shock wave turns into turbulence, the air is weakly compressible, and the laser will be distorted when it is transmitted in the air, and the intensity will attenuate. In this paper, Gaussian beam is used as the beam source, combined with Rytov theory, the expression of the intensity of Gaussian beam propagation in weakly compressible flow is derived. The results show that air density is an important factor affecting the attenuation of intensity, and the influence of air pressure cannot be ignored. Increasing the beam waist width can resist the attenuation of intensity to a certain extent. It is different from the turbulent atmosphere that the beam attenuation is greater in weakly compressible flows, which must be considered when discuss the attenuation of aerospace communication signals.
In recent years, for the development or application of vortex beams and spatial structured optical fields, the detection of orbital angular momentum (OAM) of vortex beams has become an important topic. In this paper, based on the holographic diffraction grating method of the spatial light modulator (SLM), through a designed diffraction grating whose intensity distribution and diffraction angle are adjustable, the OAM of the single-mode vortex beam is detected. We first started with a self-designed 1D holographic diffraction grating, verified our ideas, and then designed a 2D holographic diffraction grating and successfully detected the OAM of the single-mode vortex beam. The theory and experiment are in great agreement. Our method is useful for the design of SLM-based holographic diffraction gratings and has reference value for OAM detection and data transmission systems based on vortex beams.
In the plume spectrum of hydrogen-oxygen fuel, the radiation spectrum of hydroxide radical (OH) is an obvious feature in the ultraviolet (UV) band. Since the control temperature can be determined by the relative intensity of a single transition, the Hitran database is used to analyze the OH spectrum structure, then two sets of temperature-sensitive peaks are found, corresponding to the OH (A2 Σ,v' = 0→X2 Π,v'' = 0) and OH (A2 Σ,v' =1→X2 Π,v'' =1) transitions, respectively. The law of the two groups of peaks with temperature is analyzed in the temperature range of 600-3300K, and the method of determining the control temperature can be obtained by knowing the relative intensity, which provides a way for the temperature inversion in the ultraviolet band.
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