Influence Of Coherence Length Research Articles

Properties of partially coherent elegant Laguerre-Gaussian beam in free space and oceanic turbulence

The analytical expression of partially coherent elegant Laguerre-Gaussian (PCELG) beam generated by anisotropic Gaussian Schell-model sources is given. The analytical formulas of CSD for a PCELG beam propagating in free space and oceanic turbulence are derived. The characteristics of average intensity and spectral degree of coherence of a PCELG beam propagating in free space and oceanic turbulence are investigated by using numerical simulations. It is shown that the stronger oceanic turbulence will accelerate the evolution of a PCELG beam propagating in oceanic turbulence, and the influences of coherence length on the spectral degree of coherence will disappear as the propagation distance increases. The findings may be useful in underwater optical communications.

Evolution properties of a radial phased-locked partially coherent Lorentz-Gauss array beam in oceanic turbulence

The concept of a radial phased-locked partially coherent Lorentz-Gauss array (PCLGA) beam generated by a Schell-model source has been introduced. Based on the Huygens-Fresnel principle, the analytical expressions for the cross-spectral density function of a radial phased-locked PCLGA beam propagation in oceanic turbulence has been derived. The average intensity and coherence properties of a radial phased-locked PCLGA beam propagating in oceanic turbulence are illustrated using numerical examples. The influences of coherence length and oceanic turbulence on the evolution properties and spectral degree of coherence are analyzed in details. The results show that radial phased-locked PCLGA beam propagation in stronger oceanic turbulence will evolve into Gaussian-like beam more rapidly as the propagation distance increases.

Propagation of partially coherent Lorentz-Gauss vortex beam through oceanic turbulence.

The partially coherent Lorentz-Gauss vortex beam generated by a Schell-model source has been introduced. Based on the extended Huygens-Fresnel principle, the cross-spectral density function of a partially coherent Lorentz-Gauss vortex beam propagating in oceanic turbulence is derived. The influences of coherence length, topological charge M, and oceanic turbulence on the spreading properties and position of the coherence vortex for a partially coherent Lorentz-Gauss vortex beam are analyzed in detail. The results show that a partially coherent Lorentz-Gauss vortex beam propagating in stronger oceanic turbulence will evolve into a Gaussian-like beam more rapidly as the propagation distance increases, and the number of coherent vortices will change.

Propagation properties of a partially coherent Lorentz beam in uniaxial crystal orthogonal to the optical axis.

The cross-spectral density function of a partially coherent Lorentz beam propagating in uniaxial crystal orthogonal to the optical axis is obtained, and the evolution properties and the spectral degree of coherence for a partially coherent Lorentz beam in uniaxial crystal are illustrated by using numerical examples. The influence of coherence length and the ratio of refractive index ne/no on the normalized intensity and spectral degree of coherence for a partially coherent Lorentz beam are analyzed in detail.

Evolution properties of partially coherent four-petal Gaussian beams in oceanic turbulence

Based on the extended Huygens–Fresnel integral formula, the analytical expressions for partially coherent four-petal Gaussian beam propagating in oceanic turbulence are derived, and the influences of coherence length, beam order N and the parameters of oceanic turbulence (the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the rate of dissipation of mean square temperature and the relative strength of temperature and salinity fluctuations) on average intensity properties are investigated using numerical examples in detail. The results show that the beam with the higher beam order N or coherence length will lose its initial four-petal profiles slower. It is also indicated that the beam will evolve into a Gauss-like beam more rapidly with increasing oceanic turbulence strength. The results have the potential application in underwater laser communication using a partially coherent four-petal Gaussian beam.

Influence of coherence length, signal-to-noise ratio, log transform, and low-pass filtering on layer thickness assessment with OCT in the retina.

Optical coherence tomography (OCT) images of the retina are inevitably affected by the finite width of the coherence function and noise. To make low-reflective layers visible, the raw OCT signal is log transformed; to reduce the effect of noise the images can be low-pass filtered. We determined the effects of these operations on layer thickness assessment, as a function of signal-to-noise ratio (SNR), by performing measurements in a phantom eye and modeling. The log transform appeared to be the key factor in a SNR-dependent overestimation of peak widths and a less predictive bias in the widths of low-reflective layers.

Propagation Properties of a Partially Coherent Flat-Topped Vortex Hollow Beam in Turbulent Atmosphere

Using coherence theory, the partially coherent flat-topped vortex hollow beam is introduced. The analytical equation for propagation of a partially coherent flat-topped vortex hollow beam in turbulent atmosphere is derived, using the extended Huygens-Fresnel diffraction integral formula. The influence of coherence length, beam order N, topological charge M, and structure constant of the turbulent atmosphere on the average intensity of this beam propagating in turbulent atmosphere are analyzed using numerical examples.

Evolution properties of partially coherent flat-topped vortex hollow beam in oceanic turbulence.

Employing the theory of coherence, the partially coherent flat-topped vortex hollow beam is first introduced. The analytical propagation equation for a partially coherent flat-topped vortex hollow beam in oceanic turbulence is derived by using the extended Huygens-Fresnel diffraction integral and the spectrum of oceanic turbulence. The influences of coherence length, beam order N, the topological charge M, and the parameters of oceanic turbulence on evolution properties of partially coherent flat-topped vortex hollow beams propagating in oceanic turbulence are obtained by using the numerical examples.

Partially coherent vortex beams focused by an aperture lens with coma

We investigate the influence of the coma of the lens on the focusing of partially coherent vortex beams. On the basis of the generalized Huygens-Fresnel diffraction integral, the formula for the intensity distribution in the focal plane is derived. The numerically calculated results are given to show that the coma of the lens leads to the asymmetry of focused intensity distribution. The influence of coherence length on the focused intensity distribution is also investigated. It is found that the effect of coma is not obvious when the coherence length is small. Intensity profiles for three different values of the azimuthal angle are plotted to illustrate the effect of coma and the influence of coherence length.