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In this paper, we present the experimental generation of Airy beams via computational and photorefractive holography. Experimental generation of Airy beams using conventional optical components presents several difficulties and are practically infeasible. Thus, the optical generation of Airy beams has been made from the optical reconstruction of a...
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In this work we extend the so called frozen wave method in order to obtain new diffraction resistant light structures that can be shaped on demand, with possible applications in atom guidance. The resulting beams and the corresponding optical dipole potentials exhibit a strong resistance to diffraction effects and their longitudinal and transverse...
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We theoretically examine the temporal behavior of novel Airy beams, their interactions, and their dependence on thermal energy associated with diffusive nonlinearity in photorefractive media. For the first time, it is examined under the time-dependent diffusive-saturable nonlinear Schrödinger equation (DSNLSE). The results show that optical Airy beam propagation is effectively controlled by illumination time. In long propagation distance, the significant illumination time of the thermal energy-independent optical Airy beams associated with diffusive nonlinearity lead to unstable self-deflection soliton beams over the increasingly intense competition between photorefractive nonlinearity and diffusive nonlinearity. Meanwhile, in short propagation distance, optical Airy beams were found to maintain their acceleration over a certain distance as time increased. The temporal behavior of the interaction of optical Airy beams shows that in phase, they are affected by illumination time, while out of phase, they show almost no significant changes. We find that fusion solitons eventually emerge in phases. On the other hand, we also find that this self-trapped wave packets self-bend during propagation with an acceleration rate that depends on the thermal energy associated with diffusive nonlinearity. Finally, we found that the study results agreed well with previous experiments and studies.
We solve the traveling wave solution for the explicit-time nonlinear photorefractive dynamics equation. Nonlinearity comes from the support of linear and quadratic electro-optic effects. We investigate two cases, i.e., the wave assumes to be in low amplitude and without such an assumption. In this step, we apply the direct solution method by setting the ansatz of the wave solution from the start. The first case relies on the Taylor series expansion to integrate the equations of these results and get an exact solution for the traveling wave. In the second case, we thoroughly evaluate the original dynamic equation. It reduces to a first-order differential equation that provides the initial conditions for a numerical evaluation. The exact solution shows the propagation wave traveling in the positive and negative directions in the diffraction axis direction. An angle between the traveling wave and the center of the propagation plane decreases as the value of the displacement constant in the solution increases. In addition, we also study the power of the traveling wave, and the numerical solution gives a kink-like traveling wave.
In this work, we optically trap micro-particles with higher-order frozen waves using holographic optical tweezers. Frozen waves are diffraction-resistant optical beams obtained by superposing co-propagating Bessel beams with the same frequency and order, obtaining efficient modeling of its shape. Based on this, we developed a holographic optical tweezers system for the generation of frozen waves, and with this, it was possible to create traps in a stable way for the trapping and guiding of micro-particles in the transverse plane. The experimental results show that it is possible to obtain an excellent stability condition for optical trapping using higher-order frozen waves. These results indicate that frozen waves are promising for optical trapping and guiding of particles, which may be useful in various applications such as biological research, atomic physics, and optical manipulations using structured light with orbital angular momentum.
Vortex beams can potentially be used in optical communication, imaging, and processing applications, herein, we propose a method to generate a phased Gaussian optical array (PGOA) by arranging an aperture-bounded Gaussian optical array along arbitrary curves and using a discontinuous phase to form a controllable vortex phase. The phase difference between adjacent sub-beams is constant, and the total phase increment is 2πl. The experimental limitations of this technique are discussed, including the aperture radius, off-axis distance, number of sub-beams, and maximum topological charges. The coaxial interference characteristics of the PGOA in free space were examined numerically by using a split-step Fourier transform algorithm. We theoretically and experimentally proved the feasibility of a coherent beam combination scheme to generate a PGOA, which is of particular significance for particle manipulation and free-space optical communication applications.
A full analytical theory for the reflection and transmission of an Airy beam impinging on a dielectric surface is presented. Based on the plane-wave angular spectrum expansion, the analytical expressions for the reflected and transmitted fields comprising beam modes are derived. To improve the calculation accuracy, the actual beam field retains up to the second-order terms. The influences of decay factor and beam width on the intensity distributions of the incident, reflected, and transmitted beams are studied. In addition, we investigate the effects of decay factor and beam width on the beam shift of the reflected beam near the Brewster angle. There is a giant negative lateral shift near the Brewster angle. Results show that the beam shift decreases and increases with increasing decay factor and beam width, respectively. A comparison with the beam shifts of Airy beams incident on the interface and dielectric slab at the Brewster angle is also discussed. The beam shift of the dielectric slab exists an abrupt increase. Finally, an Airy beam incident from air to the left-handed material (LHM) is considered. Results indicate that the imaging position of the incident Airy beam in the LHM is affected by the incident angle and negative refractive index. Our results may provide some theoretical support for the applications of Airy beams in detection and imaging.
The intensity distribution of four-petal Gaussian vortex (FPGV) beams through a focused optical system and the radiation force acting on a Rayleigh dielectric sphere is obtained based on the extended Huygens–Fresnel principle and the Rayleigh scattering theory. We mainly study the trapping of high and low refractive index Rayleigh particles by FPGV beams and the effect of the topological charge $m$ m on the radiation force. The results show that the specific distribution of the incident beam can be controlled by a reasonable choice of topological charge $m$ m . The multiple locations in a beam of light where particles of different refractive indices can be captured will be found. On the other hand, when $m$ m changes, the number of particles captured and the locations where they can be captured change accordingly. Therefore, the flexibility to simultaneously capture multiple Rayleigh particles with different refractive indices with a single beam at different locations in the focal plane can be achieved using the FPGV beam.
Hole-electron competition was induced in an undoped Bi12TiO20 crystal using coherent pre-illumination at 532 nm. Photorefractive recording and erasure at 639.7 nm under the action of external electric field E0 were used to theoretically and experimentally investigate the competition within the sample band-gap. The good agreement between theory and experimental data allowed to obtain, in both regimes without and with pre-illumination, the saturation space-charge fields Eq and holes and electrons effective donors concentrations (ND)eff's. The phase shift between the electronic gratings and the hole grating was also computed and revealed a competition behavior between the applied electric field effect of increasing the characteristic lengths of electrons and holes moving in opposite directions in the conduction and valence bands, respectively, and the intensity of decreasing such lengths. The computed holes donor density indicated a strong contribution of the coherent pre-illumination to the hole-electron competition mechanism.
Flow cytometry is an essential technique in biomedical discovery for cell counting, cell sorting, and biomarker detection. In vivo flow cytometers based on one-photon or two-photon excited fluorescence have been developed for over a decade. One drawback of the laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is limited to the focal spot due to the short Rayleigh range of focused Gaussian beams. Hence, the sampling volume is much smaller than in one-photon flow cytometers, making it challenging to count or detect rare circulating cells in vivo. Non-diffracting light waves like Bessel beams and Airy beams have narrow intensity profiles with an effective spot size as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making them an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Airy beams rather than Gaussian beams is side lobes Airy beams have, which contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using 2D Airy beams to form a light-sheet that intersects the blood vessel a microfluidic channel, which was used to model a blood vessel. The setup can successfully detect and count flowing fluorescent microspheres in a microchannel.
Airy transformation is a useful technique to modulate amplitude and phase of a light beam, which has important applications in particle trapping/manipulation, optical communications and optical imaging. However, most of the studies only focused on the Airy transform of Gaussian beams and other vortex-free beams in the past. In this paper, the Airy transform of Gaussian vortex beams, which are the most common vortex beams, is investigated. A universal analytical expression of the Gaussian vortex beams with topological charge (TC) m passing through an Airy transform optical system is derived. We carry out a detailed study on the output beams’ characteristics after the Airy transform of the Gaussian vortex beams with m = ± 1 and ± 2. The analytical expressions for the centroid, the beam spot size, the divergence angle and the beam propagation factor of the output beams are derived. The effects of the Airy control parameters and the TC on the normalized intensity distribution, the phase distribution, the centroid, the beam spot size and the beam propagation factor of the output beams are investigated both theoretically and experimentally. The experimental results agree reasonably well with the theoretical results which illustrate the properties of Airy transform of the Gaussian vortex beams.
