Search

International audience; We propose a method to generate beams according to transmission limitation condition by using the multi-distance phase retrieval algorithm. Propagation properties of hollow beams were determined by several intensity patterns along the travel axis. Predicted beams were obtained using a two-step phase filtering from a Gaussian beam with fundamental mode. An iterative phase retrieval method was employed for calculating the phase distribution in the filtering mask. This beam generation approach matched special propagation characteristics of the beams in practical applications.

With the development of modern precision optical fabrication and measurement technologies, optical freeform surfaces have been widely employed in different applications, especially in off-axis refl...

We introduce a class of planar random source generating ring-shaped array profiles in the far field. The model for spatial correlation function of this new source is composed by the Fourier transform of the Laguerre-Gaussian array function with circular symmetry. The analytical expressions for the spectral density (average intensity) in free space and atmospheric turbulence are derived. The effect of the source parameters on the propagation properties are investigated in detail. Numerical results show that the source can produce a ring-shaped optical array profile consisting of dark-hollow-shaped or Gaussian-like-shaped beamlets at some distance, and then keep shape-invariant for long distances in free space. The number of rings, the position of beamlets, and other features can be conveniently controlled by changing the initial source parameters. In addition, increasing the relative separation distance of each beamlet or decreasing the radius of beamlets can reduce the turbulence-induced degradation.

In coherent diffraction imaging systems, mulplex measurement on unknown object can enhance the quality of output image. We apply angular mulplexing scheme to capture several diffracting images. A tilt diffraction model is used for addressing the illumination beam in the imaging process. And an iterative phase retrieval algorithm is desingend and adopted to recover the image of sample. Numerical simulation results are provied to test the imaging method. This approach can be used to enhance the quality of reconstructed images in coherent diffraction imaging.

By utilizing the extended Huygens-Fresnel principle, we derive the analytical formulas for the cross-spectral density matrix elements of a radially polarized multi-Gaussian Schell-model (RPMGSM) beam propagating in oceanic turbulence. Effects of beam parameters and oceanic turbulence parameters on the propagation properties of RPMGSM beams are investigated in detail by numerical simulation. Our results show that the RPMGSM beam with larger beam order M has an advantage over the radially polarized Gaussian Schell-model beam for reducing turbulence-induced degradation. Compared with temperature-induced turbulence fluctuation, the salinity-induced turbulence fluctuation makes a greater contribution to the influence on propagation properties of RPMGSM beams.

The precision single point diamond turning technique has been a promising technology for generating small and medium-sized freeform optical elements with high surface quality. In this paper, we present an extremely off-axis freeform optical system with a large 10.0 mm pupil diameter and a low 3.0 F-number over a wide 28° field of view. It is composed of two freeform aluminum mirrors, which are fabricated efficiently by the single point diamond turning machine. The manufacturing strategy and parameters are estimated rationally and comprehensively, based on the freeform surface characters. The freeform aluminum mirror surface can reach submicron surface accuracy and achieve nanometer surface roughness. The final assembled prototype of the off-axis two-mirror freeform display optical system has the advantages of compactness, a broad spectrum, and good display imaging performance.

We derive several analytical expressions for the root-mean-square (rms) angular width and the M(2)-factor of the multi-sinc Schell-model (MSSM) beams propagating in non-Kolmogorov turbulence with the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. Numerical results show that a MSSM beam with dark-hollow far fields in free space has advantage over the one with flat-topped or multi-rings far fields for reducing the turbulence-induced degradation, which will become more obvious with larger dark-hollow size. Beam quality of MSSM beams can be further improved with longer wavelength and larger beam width, or under the condition of weaker turbulence. We also demonstrate that the non-Kolmogorov turbulence has significantly less effect on the MSSM beams than the Gaussian Schell-model beam.

We introduce a new kind of partially coherent beam, non-uniformly Hermite–Gaussian correlated beam, by employing a non-uniformly Hermite function to modulate the spectral degree of coherence. The evolution of such scalar beam on propagation in free space and turbulent atmosphere are investigated. It is demonstrated that the spectral intensity distributions exhibit extraordinary propagation characteristics, such as self-focusing and laterally shifted intensity maxima. The position of the maximum intensity and the intensity profile can be controlled by the order of the Hermite function. The results can be useful in free-space optical communications and beam shaping.