arXiv subjects

Hua-Jun Zhang

Publications and source records attributed to Hua-Jun Zhang.

3 recordsLinked to original sources

arXiv2021

Experimental verification of phase discontinuities induced scintillation enhancement under weak perturbations

We verify the existence of scintillation enhancement by measuring the scintillation index of a beam composed of two coherent Gaussian vortex beams with $\pm 1$ topological charges propagating through thermally induced turbulence. Further experimental research based on the reference wave interferometric method demonstrates that this phenomenon is caused by the combined effect of a screw dislocation and an infinitely extended edge dislocation, namely the impact of an anisotropic dislocation. The experimental results indicate that the anisotropic dislocation is more sensitive to weak perturbations than an isotropic screw dislocation and an infinitely extended edge dislocation, which means the anisotropic dislocation has potential for weak perturbation measurement. This phenomenon is instructive in further phase discontinuity research.

physics.optics↗

arXiv2020

Outer scale of the wide-range Prandtl/Schmidt number spectrum on beam wander for oceanic optical turbulence

Light propagation in ocean is influenced by the refractive-index which is related to temperature, salinity, outer-scale, etc. Based on Hill's model 1 (H1), two kinds of oceanic refractive-index spectrum (ORIS) have been proposed to describe the second order characteristic of refractive-index. Most recently, several ORIS models were proposed based on Hill's model 4 (H4), which gave a better precision in high wave-numbers (viscous-diffusive range). However, the outer scale, as a key parameter related to practical environment, has not been introduced into any oceanic H4-based spectra. In this paper, we take the outer-scale parameter into an H4-based spectrum which is adapted to the wide-range Prandtl/Schmidt number [Opt. Express. 20, 11111(2019)]. The proposed outer-scaled spectrum could be used in analyzing wave propagation in limited outer-scaled environment with different values of average temperature and salinity. We further derived the beam wander formula of collimated laser beam. Numerical calculations show that the beam wander influenced by outer-scale length $L_{0}$ is more obvious than that influenced by average temperature $\langle T\rangle$, when $L_{0}$ varies from $10 \rm m$ to $100 \rm m$, and $\langle T\rangle$ ranges from $0^{\circ} \rm C$ to $30^{\circ} \rm C$. When salinity fluctuations prevails ($ω\rightarrow 0$), the influence of outer scale becomes weaker. In contribution proportion of beam wander, the temperature-salt coupling term is the much larger than that of temperature or salinity term.

physics.ao-ph↗

arXiv2019

Wide-range Prandtl/Schmidt number power spectrum of optical turbulence and its application to oceanic light propagation

Light influenced by the turbulent ocean can be fully characterized with the help of the power spectrum of the water's refractive index fluctuations, resulting from the combined effect of two scalars, temperature and salinity concentration advected by the velocity field. The Nikishovs' model [ Fluid Mech. Res. 27, 8298 (2000)] frequently used in the analysis of light evolution through the turbulent ocean channels is the linear combination of the temperature spectrum, the salinity spectrum and their co-spectrum, each being described by an approximate expression developed by Hill [ J. Fluid Mech. 88, 541562 (1978)] in the first of his four suggested models. The fourth of the Hill's models provides much more precise power spectrum than the first one expressed via a non-linear differential equation that does not have a closed-form solution. We develop an accurate analytic approximation to the fourth Hill's model valid for Prandtl/Schmidt numbers in the interval [3, 3000] and use it for the development of a more precise oceanic power spectrum. To illustrate the advantage of our model, we include numerical examples relating to the spherical wave scintillation index evolving in the underwater turbulent channels with different average temperatures, and, hence, different Prandtl numbers for temperature and different Schmidt numbers for salinity. Since our model is valid for a large range of Prandtl number (or/and Schmidt number), it can be readily adjusted to oceanic waters with seasonal or extreme average temperature and/or salinity or any other turbulent fluid with one or several advected quantities.

physics.ao-ph↗