Intensity Distribution Of Beam Research Articles

Paraxial propagation of cosine-hyperbolic-Gaussian beams in a chiral medium

The properties of a linearly polarized cosine-hyperbolic-Gaussian beam (ChGB) propagating in a chiral medium are investigated theoretically by using the Huygens-Fresnel diffraction integral. Beam intensity distribution characteristics in the chiral medium are discussed with numerical examples. The linearly polarized ChGB is found to split into a superposition of left and right circularly polarized Gaussian components, and its intensity pattern exhibits a variable shape depending on the chirality factor and decentered parameter b. The output beam can exhibit a richer intensity pattern compared to the Gaussian beam. The results could be beneficial for the application of ChGB in beam shaping and optical micromanipulation.

Perturbation of V-point polarization singular vector beams

The structured beams of light endowed with vector field singularities can be expressed as a superposition of spin and orbital angular momentum states. This article investigates the effect of perturbation of vector field singularities by superposing it with a homogeneously polarized beam and discusses its possible applications in studying the chiroptical effects. This perturbation leads to the splitting of vector field singularities (V-points) into stable lower-index ellipse field singularities (C-points). The strength of perturbation decides the separation between the two C-points in the resultant beam. It is found that the unfolding of V-points into lower-index C-points is always accompanied by a measurable centroid shift in the total and component intensity distribution of the resultant beam. Moreover, the centroid shift is more pronounced in the component intensity, whose state of polarization matches the state of polarization of the perturbing beam. The strength of perturbation can be measured by analyzing the radial shift in the centroid of the beam. It is observed that in the process of perturbation, the polarization singularity index is always conserved while the net helicity in the resultant beam is decided by the helicity of the perturbing beam. The strength of the perturbing beam can be modified by introducing a chiral sample in the beam path which may be useful to investigate the chiroptical effects.

Melanin effect on light beam intensity distribution in skin as a function of wavelength and depth from 200 to 1000 nm using Monte Carlo simulation

Light beam propagation inside biological tissue, is crucial for many fields. Giving that, we had investigated the effect of melanin, on light propagation inside different type of tissue. We had constructed phantoms that approximates a real tissue and mimic its reaction to light. The skin model of seven layers takes into consideration the volume fractions and optical properties of blood, water, and melanin content. We developed a Monte Carlo simulation to investigate the intensity distribution inside tissues of a light beam. The study is done for different Fitzpatrick skin types. We provide the intensity distribution and the penetration depth in the 200–1000 nm wavelength range.

Terahertz vortex beams generated by the ring-arranged multilayer transmissive metasurfaces

We propose a multilayer “H” type cell structure to construct a vortex beam metasurface generator. Based on the Pancharatnam-Berry phase theory, we propose a uniform annular arrangement to achieve a vortex beam with high transmission efficiency. At 0.1 THz frequency, the transmission efficiency reaches 62%. We further utilized printed circuit board technology to prepare samples of vortex beam generators. Using a self-built terahertz test platform, we tested the transmission beam intensity distribution characteristics of the sample. The metasurface vortex beam generator can realize the miniaturization and integration characteristics of the device, and is expected to be applied to the field of terahertz communication.

Generation, Transmission, and Amplification of OAM Modes in the PbSe-Doped Ring-Core Fiber Carrying 3D Printed Spiral Phase Plate

Vortex beams carrying orbital angular momentum (OAM) have increasingly attracted attention in the field of optical communication. However, transmission is still an issue due to transmission loss, especially in optical fibers. In this work, we proposed, designed, and fabricated micro spiral phase plates (SPPs) directly on an end facet of a piece of PbSe-doped ring-core fiber (RCF) through two-photon polymerization, realizing the integration of OAM beam generation, transmission, and amplification. The prepared RCF comprises a double-clad structure with a core-clad refractive index difference of 2.2% and the fluorescence range is 1150 nm–1700 nm. The intensity distribution of the OAM beam and the spiral interference fringes were obtained, which indicated that the OAM mode (|l|=1, 2, 3, 4) was generated and transmitted directly within the fiber. The small-signal amplification of four OAM modes was accomplished at 1550 nm under a pump power of 634 mW. The on–off gain is >13.2 dB for all modes and the differential mode gain (DMG) is <1.7 dB. The SPP-carrying RCF structure demonstrates the integration of generation, transmission, and amplification of higher-order OAM modes in all-fiber systems.

Monitoring of the heavy-ion beam distribution using poly- and monochromatic x-ray fluorescence imaging.

In this work, the first proof of the principal of an in situ diagnostics of the heavy-ion beam intensity distribution in irradiation of solid targets is proposed. In this scheme, x-ray fluorescence that occurs in the interaction of heavy-ions with target atoms is used for imaging purposes. The x-ray conversion to optical radiation and a transport-system was developed, and its first test was performed in experiments at the Universal Linear Accelerator in Darmstadt, Germany. The Au-beam intensity distribution on thin foils and Cu-mesh targets was imaged using multiple x-ray pinholes (polychromatic imaging) and 2D monochromatic imaging of Cu Kα radiation by using a toroidally bent silicon crystal. The presented results are of importance for application in experiments on the investigation of the equation of states of high energy density matter using high intensity GeV/u heavy-ion beams of ≥1010 particles/100ns.

Determining the topological charge of optical vortex by intensity distribution of a quasi-Airy vortex beam

Determining the orbital angular momentum state or the topological charge (TC) of a vortex beam is important in exploiting its applications. By analyzing the intensity distribution of the quasi-Airy vortex beam (QAVB) in far field, we find that the number of forked fringes is equal to the TCs of the vortex beam, and the direction of the forked fringes is related to the sign of TCs. Based on this property, a method of measuring the TC of optical vortex by the intensity distribution of QAVB is proposed. The range of initial topological angle (from 0 to 73°) for determining the TC of optical vortex is obtained as well as the relationship between the optimal propagation position and the initial topological angle to observe the forked fringes. In addition, the characteristics of QAVB embedded with multiple optical vortices at different locations would provide a new possibility for improving the confidentiality and the information capacity in free space optical communication.

Melt flow and cutting front evolution during laser cutting with dynamic beam shaping

A dramatic increase in the industrial demands for tailoring the laser beam profile in laser cutting has led to significant performance improvements thanks to the recently emerging dynamic beam shaping technology. Nonetheless, the underlying reasons for such process improvements are not fully understood yet, and mainly theoretical assumptions are available. This paper uses several high-speed videography strategies to evaluate and compare the melt flow dynamics and cutting front geometry during 4 kW fiber laser cutting of 15 mm plates with static and oscillating beams. The absorption behavior on the cutting front is analyzed through trim-cut observation, and a substantial difference of around 40% is observed between these two laser beam intensity distributions. Moreover, a distinctive molten material ejection mechanism is found during linear beam oscillation, being beneficial for fusion cutting and detrimental for flame cutting. Finally, based on the experimental results, a former explanatory model from the literature is enhanced and further ways to optimize the beam profile during laser cutting are proposed.

Evolution Properties of a Partially Coherent Twisted Laguerre-Gaussian Pulsed Beam Propagating through Anisotropic Atmospheric Turbulence

Analytical expressions for the cross-spectral density matrix of a partially coherent twisted Laguerre-Gaussian pulsed (PCTLGP) beam in anisotropic atmospheric turbulence are derived based on the extended Huygens–Fresnel principle. Numerical results indicate that the atmospheric turbulence induces the degeneration of the spectral intensity distribution of the PCTLGP beam, and the PCTLGP beam also shows different evolution properties on propagation in weaker turbulence and stronger turbulence. The PCTLGP beam with a negative twisted factor exhibits an advantage over the Laguerre-Gaussian pulsed beam for reducing the atmospheric turbulence-induced degeneration, and this advantage is further strengthened with increasing the topological charge, mode order and absolute value of the twisted factor. In addition, we also find that the pulse duration will affect the spectral intensity of the PCTLGP beam in turbulence. This kind of beam will show potential application value in free-space optical communications and remote sensing.

Improved photoacoustic images via wavefront shaping modulation based on the scattering structure.

Multispectral optoacoustic tomography (MSOT) has become the dominant technical solution for photoacoustic imaging (PAI). However, the laser source of fiber output in the current MSOT method is typically a TEM00 Gaussian beam, which is prone to artifacts and incomplete due to the uneven distribution of the irradiated light intensity. Here, we propose a novel method to improve the quality of photoacoustic image reconstruction by modulating the wavefront shaping of the incident laser beam based on the designed scattering structure. In the experiment, we add the designed scattering structure to the current hemispherical photoacoustic transducer array device. Through experiments and simulations, we investigate and compare the effects of different scattering structures on laser intensity modulation. The results show that an ED1-C20 diffusion structure with a scattering angle of 20 degrees has the most effective modulation of the beam intensity distribution. And we choose gold nanoparticles of 50-100 nanometers (nm) diameters and index finger capillary vessels respectively as the medium of PAI. We obtain the highest ratio of PAI area increases of gold nanoparticles and index finger to devices compare without scattering structure is 29.69% and 634.94%, respectively. Experimental results demonstrate that our method is significantly higher quality than traditional methods, which has great potential for theoretical application in medical PAI.

Fiber laser cutting of steel materials with twin spot beam-twin spot setting in kerf width direction

In laser cutting, the temperature distribution would have significant influence on cutting characteristics, and the intensity distribution of a laser beam has a possibility to improve the cutting quality. In this study, a fiber laser beam of Gaussian distribution was divided into two beams by a roof axicon lens, and the cutting characteristics were investigated by using the twin spot Gaussian beam setting in the kerf directions. The cutting experiment of a cold-rolled steel plate with a thickness of 3.2 mm was carried out by a 3 kW fiber laser with a nitrogen assist gas, and the Gaussian mode of 114 μm spot and the twin Gaussian mode of two 110 μm spots were used with the variation of power ratio in twin spot processing. At the exit side of kerf by the twin spot process, the width of the cutting front in the low intensity side became wider than that in the high intensity side, and the dross could be reduced in the low intensity side due to sufficient ejection of the molten metal from the front wall rather than the side wall of kerf. The twin spot process could reduce the dross height below 18 μm in the low intensity side, which is smaller than that by the single Gaussian beam process.

Analysis of Azimuthal Doppler Shift of Anisotropically Absorbed Laguerre-Gaussian Beam Propagating in Transverse Flow

The particle flux onto a material is an important parameter in the study of the plasma-material interaction. With conventional Doppler spectroscopy, it is difficult to measure the flow velocity perpendicular to the material because only the velocity component projected on the wave number vector can be measured. To overcome the limitation, we are developing a transverse flow measurement method using the azimuthal Doppler shift of a Laguerre-Gaussian (LG) beam absorption spectroscopy. In this paper, the feasibility of this spectroscopy method has been examined by numerical analysis. The LG beam is anisotropically absorbed in the transverse flow due to the azimuthal Doppler shift. Since the anisotropic LG beam rotates with propagation, the spatial structure of resonance absorption in plasma and the intensity structure of the LG beam that has propagated through the plasma are inevitably different in the LG beam absorption spectroscopy. It was shown that the deviation from the original azimuthal Doppler shift is reduced to several percent at the position where the intensity distribution of the LG beam reaches its maximum value. Therefore, the transverse flow can be measured with sufficient accuracy by properly selecting the position on the beam cross-section used to evaluate the azimuthal Doppler shift.

Intensity uniformity improvement for a complex line beam

A complex line beam, whose intensity distribution is uniform along a line shape and phase distribution is linearly gradient, can be applied in automatic directional transportation and optical separation of microparticles. Generally, complex amplitude beam shaping methods are used to control both the amplitude and phase of an output beam with a single phase-only element. However, for the complex line beam, although the phase gradient can be controlled well, the intensity of the beam is unevenly distributed, i.e. most of the energy of the beam is distributed in the two ends of the lateral direction. In this paper, we propose an intensity-compensation method based on the complex amplitude beam shaping method, in which the target intensity distribution of the output beam is modulated with a Gaussian profile on purpose. The simulation and experimental results show that the intensity uniformity of the complex line beam has been increased by 80.6% while the phase of the beam has been controlled as linearly gradient.

Propagation properties of chirped cosh-Gaussian beams in strongly nonlocal nonlinear media

In this paper, we analytically investigated the evolution properties of chirped cosh-Gaussian beams in strongly nonlocal nonlinear media (SNNM). The expressions describing beam propagation, intensity distribution, and beam width are derived. The results show that in the absence of chirp, the evolution behavior of beam is similar to the solitons and breathers, which closely depends on the input power and initial parameter. In the presence of linear chirp, the optical beam periodically oscillates along a certain direction and exhibits the same structure as the unchirped beam. In the presence of quadratic chirp, the center symmetry of beam evolution is broken. Furthermore, we find that the evolution of beam width always changes periodically whatever the beam power is.

Transmission dynamics of circular–linear edge dislocation solitons in nonlocal nonlinear media

In this paper, the nonlinear propagation dynamics of circular–linear edge dislocation beams (CLED beams) in nonlocal media are studied theoretically. The transport formulae of CLED beams in nonlocal nonlinear media is derived. The evolution of the beam width, curvature, and intensity distribution are discussed in detail. Two different incident cases of CLED beams, namely beam waist and non-beam waist incidences, are discussed and compared. It is found that the off-axial distance can effectively adjust the position of linear edge dislocation and play a key role on beam propagation. The initial beam power and non-beam waist distance also play a key role in propagation. In particular, when specific parameters are selected, the CLED beam can form a transmission state with beam width and transverse pattern both invariant, i.e., CLED soliton forms. For general parameters, the transverse multi-peak patterns of the CLED beam evolutes periodically, i.e., a generalized higher-order soliton or breather forms.

Thermal lens effect with light's orbital angular momentum.

Thermal lens effect has been well developed and exploited for decades by using the Gaussian intensity distribution of a laser beam. In this paper, a new thermal lens effect by using a laser beam with Orbital Angular Momentum (OAM) is proposed. We find that the dynamic process for the formation of the OAM-thermal lens has reda rapid change towards the evolution direction at the beginning but then slowly approaches to a steady state for a while. This phenomenon is significantly different from the traditional Gaussian-thermal lens, thus it may be used to improve the sensitivity of the absorption spectrum for the chemical and biomedical analysis. Besides, theoretically and experimentally, the factors affecting the steady state of the OAM-thermal lens are also studied, hoping these may provide a useful reference for the research community. We also find a potential slow thermal-optical gate that can control of light passing through or blocking by changing the OAM of the heating beam. Our work opens the door which utilizes the structured light beam to study the thermal-optical effect, and more interesting phenomena remain to be explored.

The multi-consecutive optical bottles generated from the chirped elliptical Pearcey Gaussian vortex beams

The evolution of the chirped elliptical Pearcey Gaussian vortex (CEPGV) beams in free space is numerically investigated. The optical bottle and multi-consecutive optical bottles can be directly generated from an elliptical Pearcey Gaussian beam with central vortices and the second-order chirp. In particular, the focusing intensity of CEPGV beams will increase when the elliptical structure deflects larger or the ratio of the long axis to the short axis of the ellipse is larger. Furthermore, we can obtain multi-consecutive optical bottles by manipulating elliptical structure parameters and second-order chirp factors. In the meantime, the transverse intensity distributions at foci of CEPGV beams appear like a slit in a fixed direction. Our results show that the focusing intensity, the focal length and the transverse intensity distribution of CEPGV beams during the propagation can be controlled.

Polarization and coherence properties in self-healing propagation of a partially coherent radially polarized twisted beam.

With the help of generalized Huygens-Fresnel integral, an analytical expression for the self-healing of a partially coherent radially polarized twisted (PCRPT) beam is derived. The coherence and polarization properties of the PCRPT beam in self-healing propagation are studied in detail. It shows that the existence of the twist phase is a double-edged sword for the self-healing properties of the beam. With the increase of the twist factor, the self-healing ability of beam intensity distribution decreases. However, the anti-disturbance performance of beam polarization improves at the same time. Besides, the polarization and coherence distribution of the beam are proved that own a slight self-healing ability when the obstacle is small. Our results will be helpful to the fields of optical tweezers, microscopy, optical communication, and so on.

Diffractive deep neural network based adaptive optics scheme for vortex beam in oceanic turbulence.

Vortex beam carrying orbital angular momentum (OAM) is disturbed by oceanic turbulence (OT) when propagating in underwater wireless optical communication (UWOC) system. Adaptive optics (AO) is a powerful technique used to compensate for distortion and improve the performance of the UWOC system. In this work, we propose a diffractive deep neural network (DDNN) based AO scheme to compensate for the distortion caused by OT, where the DDNN is trained to obtain the mapping between the distortion intensity distribution of the vortex beam and its corresponding phase screen representing OT. In the experiment, the distorted vortex beam is input into the DDNN model where the diffractive layers are solidified and fabricated, and the intensity distribution of the modulated light field of the vortex beam can be recorded. The experiment results show that the proposed scheme can extract quickly the characteristics of the intensity pattern of the distorted vortex beam, and the predicted compensation phase screen can correct the distortion caused by OT in time. The mode purity of the compensated vortex beam is significantly improved, even with a strong OT. Our scheme may provide a new avenue for AO techniques, and is expected to promote the communication quality of UWOC system immediately.

Folded Resonator for Glucose Solution Density Detection Based on Airy Beam Arrays

We presented an investigation on the evolution properties of the finite Airy beam array (FAiBA) in metamaterial’s slab system constituting of right-handed materials and double negative materials combining the generalized Huygens–Fresnel integral equation and the light transfer matrix. The beam intensity distribution on the receiver plane and its side transmission view on the (z, x) plane are demonstrated numerically with several array numbers. Moreover, we put forward a kind of folded resonator to detect glucose solution density based on the derived principle and conclusion; the influence of curvature radius on the emerging beam’s evolution characteristics is discussed, and the empirical formula between FAiBA’s received power and glucose solution density is derived by using the fit linear analysis. We hope that the present concept and the derived conclusions can be employed for monitoring in the environmental field, as well as the biomedical and food safety detection.