Gaussian Irradiance Distribution Research Articles

High forward thrust metasurface beam-riding sail.

The radiation pressure force and torque on a one-dimensional bi-grating composed of a Si-SiO2 high contrast binary metagrating is analyzed for the purpose of stable beam riding whereupon a high power laser having an expanding Gaussian irradiance distribution propels the grating in outer space, free from gravitational forces. The binary metagrating structure has been simultaneously optimized to afford high forward thrust, and corrective restoring forces and torques in the event of small linear and angular disturbances. We demonstrate that stability may be enhanced at the expense of forward thrust. The validity of our metamaterial findings is reinforced owing to good agreements between finite-difference time-domain and finite element numerical methods. To reduce mass and enhance forward acceleration this laser-driven sail was designed to be free of a stabilizing boom.

Two-dimensional axisymmetric opto-thermal phosphor modeling based on fluorescent radiative transfer equation

Remote phosphor plate excited by the light-emitting diode (LED) or laser diode (LD) has been widely applied in solid-state lighting. The light propagation properties within the phosphor have been analytically characterized based on the one-dimensional assumption. However, this may be not feasible in some cases, e.g., the excitation spot diameter is comparable to the plate thickness or the incident irradiance is not uniform along the horizontal direction. In this work, we extend the one-dimensional model to a two-dimensional axisymmetric opto-thermal model based on the fluorescent radiative transfer equations (FRTEs) for the cylindrical phosphor plate excited by a collimated beam with a small spot diameter and Gaussian irradiance distribution. The radiances of the blue and yellow lights are iteratively calculated by solving FRTEs in the cylindrical coordinate system using the discontinuous spectral element method. By inputting the obtained heat generation density from FRTEs, we calculate the three-dimensional temperature distribution by solving the heat diffusion equation (HDE). In addition, the opto-thermal interaction between FRTEs and HDE is achieved by introducing the temperature-dependent phosphor quantum efficiency. Using the model, we evaluate the optical, thermal and opto-thermal interacted performances of the phosphor. Finally, the model is validated by comparing the measured output optical power and surface temperature distribution with the calculated results.

An autonomous optimal control strategy for reducing Gaussian laser beam constraint effect on photovoltaic array

A novel autonomous optimal control strategy on a photovoltaic array under a Gaussian beam constraint condition for a high-intensity laser power beaming system is proposed in this paper. The proposed strategy divides the PV array into several concentric parallel branches according to Gaussian irradiance distribution and optimizes the series and parallel forms of each concentric branch and its PV cells, which is not dependent on the specific PV array topology and can obtain an optimal connection form matching with the system under Gaussian beam constraint condition. The proposed strategy can be applied to the different connection forms of PV array for minimizing the Gaussian constraint effect by utilizing the characteristics of Gaussian irradiance distribution on laser facula and the inherent error values in the matching area of the laser facula and the PV array, and the output power and the efficiency of PV array can reach an optimal value simultaneously. The uneven irradiance of Gaussian laser facula is mathematically modeled in this paper. The correctness of theoretical analysis is verified by simulation results.

Improvement of Galilean refractive beam shaping system for accurately generating near-diffraction-limited flattop beam with arbitrary beam size

We propose and demonstrate the improvement of conventional Galilean refractive beam shaping system for accurately generating near-diffraction-limited flattop beam with arbitrary beam size. Based on the detailed study of the refractive beam shaping system, we found that the conventional Galilean beam shaper can only work well for the magnifying beam shaping. Taking the transformation of input beam with Gaussian irradiance distribution into target beam with high order Fermi-Dirac flattop profile as an example, the shaper can only work well at the condition that the size of input and target beam meets R(0) ≥ 1.3 w(0). For the improvement, the shaper is regarded as the combination of magnifying and demagnifying beam shaping system. The surface and phase distributions of the improved Galilean beam shaping system are derived based on Geometric and Fourier Optics. By using the improved Galilean beam shaper, the accurate transformation of input beam with Gaussian irradiance distribution into target beam with flattop irradiance distribution is realized. The irradiance distribution of the output beam is coincident with that of the target beam and the corresponding phase distribution is maintained. The propagation performance of the output beam is greatly improved. Studies of the influences of beam size and beam order on the improved Galilean beam shaping system show that restriction of beam size has been greatly reduced. This improvement can also be used to redistribute the input beam with complicated irradiance distribution into output beam with complicated irradiance distribution.

Multiplicity and contiguity of ablation mechanisms in laser-assisted analytical micro-sampling

Laser ablation is implemented in several scientific and technological fields, as well as a rapid sample introduction technique in elemental and trace analysis. At high laser fluence, the ejection of micro-sized droplets causes the enhancement of the surface recession speed and depth resolution degradation as well as the alteration of the sampling stoichiometry. The origin of such large particles seems to be due to at least two different processes, phase explosion and melt splashing. Experimental evidence for both was found in metallic matrices, whereas non-metallic samples showed more complex phenomena like cracking. The spatial distribution of the beam energy profile is responsible for significant differences in the ablation mechanism across the irradiated region and for heterogeneous sampling. Under Gaussian irradiance distribution, the center of the crater, where the irradiance is the highest, experienced a fast heating with rapid ejection of a mixture of particles and vapor (spinodal breakdown). The crater periphery was subjected to more modest irradiation, with melt mobilization and walls formation. The overall resulting particle size distribution was composed of an abundant nano-sized fraction, produced by vapor condensation, and a micro-sized fraction during melt expulsion.

Microstructural characterization of autogenous laser welds on 316L stainless steel using EBSD and EDS

This research is concerned with autogenous welding of 316L stainless steel and the microstructure generated by such a process. Autogenous welding does not require a filler material and in this case relies on an initial shallow melt phase to maintain a conduction limited weld. Essentially, a high power laser beam traverses the substrate, with the beam shaped by conventional optics, which produces a Gaussian irradiance distribution; or with a diffractive optical element, used to produce a uniform irradiance distribution. Initial results have shown that due to the nature of the heating cycle, complex microstructures are developed. These fine, complicated microstructures cannot be satisfactorily resolved and quantified using standard optical microscopy techniques. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) have been carried out on a number of different microstructures prepared using a range of welding parameters. It is demonstrated that the simultaneous determination of the chemistry and crystallography is a very useful tool for rapid identification of the different phases formed on solidification as a consequence of varying welding procedures.

Signal response of a laser beam scanner

A laser beam scanner, used as an angle measuring device in a particular navigation system for mobile robots, has been developed. It measures heading angles to beacons made of vertical stripes of retroreflective tape. Expressions giving the received power and energy in the pulse, which is generated when a beacon is traversed by the laser beam, are given. Measurements support the derived expressions. The shape and amplitude of the pulse are functions of the range <i>R</i> to the beacon, but at long range the pulse shape and width become independent of range while the dependence of the received amplitude on range becomes <i>R</i>^-3. At long range the pulse shape is determined by the Gaussian irradiance distribution in the laser beam and the pulse width is governed by the laser beam divergence and the scanning speed. Design rules for the optimum field of view of the receiving optics and for an electrical filter, which maximizes the signal-to-noise ratio, are proposed. An expression giving a conservative estimate of the signal-to-noise ratio is derived.

Focal depth of a transmitting axicon*

The transmitting axicon is examined for the axial field distribution of a regular axicon when the incident wave is plane and uniform, and when it has a gaussian irradiance distribution. In the microwave region, the focal depth of an axicon does not differ very much from that of a perfect lens. In the visible region, the axicon possesses a much greater focal depth, which can be greatly changed by changing the curvature of the slanting side of the axicon. For an axicon with a straight slanting side and small height, when a gaussian incident wave is used, the irradiance at the principal focus varies inversely with the focal length.

Characteristic Parameters of a Beam with a Gaussian Irradiance Distribution

This describes a simple method to find two important characteristic parameters of a beam with a Gaussian irradiance profile—the position of the plane of the beam waist and the value of ω0 in that plane. It is necessary to observe the positions of maximum or minimum irradiances along the beam axis in the field diffracted by a circular aperture. These positions occur at places where the direct geometric-optical wave is in phase or out of phase with the boundary-diffraction wave.

Field of a Truncated Gaussian Beam as Given by the Boundary-Diffraction-Wave Theory

The field of an incident wave with a Gaussian irradiance distribution diffracted by a circular aperture has been evaluated by using the boundary-diffraction-wave theory. Numerical results of the irradiance distributions, both along the axis and in transverse planes, are compared with those given by the Kirchhoff integral. Good agreement is obtained in all cases over wide regions of the diffracted field.