Laser Facula Research Articles

Simulation of defocusing effect based on two-step ABCD algorithm while a modal decomposition

Depicting the multimode laser beam by modal decomposition can potentially assess light field variations in the fiber, during propagation. The practical engineering conditions in the lab however could not realize ideal levels, hence further research on factors influencing this method, such as defocus, is especially necessitated. The grid spacing in observation plane by Fast Fourier Transform is fixed and unchangeable within diffraction imaging, hence possibly yielding erroneous data during obtaining light field intensities. Our research resolves these issues via a Two-step ABCD algorithm, applied in the modal decomposition to characterize various guided modes at the output of multimode fibers. A direct benefit is that the image plane size can be altered, further refining laser facula clarity. Furthermore, the quantitative expressions that analyze defocus factors impacting modal decomposition are acquired. The conclusions thereby prove the modal decomposition algorithm can keep effectiveness in the range of −0.25% to 0.25% of relative defocus for low order eigenmodes, having no suitable limited band for high order eigenmodes, with reference value in engineering applications.

Research on beam bunching and deflection characteristics of low-power laser under the electromagnetic effect

The bunching and deflection characteristics of low-power laser beam were investigated under electromagnetic field. On the basis of the Faraday effect, the cylindrical electromagnetic cavity was designed and implemented in the experiments. Several types of the magneto-optical elements were placed in the electromagnetic cavity individually. In the test of the deflection characteristics of low-power laser, the rotating angle, the polarization plane of linearly polarized light which passed through electromagnetic cavity, was measured by polarization extinction. We focus on the relation between the coil current and the rotating angle. The experimental data show that when the coil current varies in the range of 0–5 A, the rotating angles changed from 0° to 24.1°. Then, a fitting formula about the coil current and the rotating angle was obtained from the experimental data using the least square algorithm. The analysis shows that the rotating angle is proportional to the excitation current and the correlation coefficient is more than 0.9995. In order to study the beam bunching characteristics of low-power laser, the area of the laser facula was measured after the low-power laser passed through the electromagnetic cavity. The experiment data show that the laser facula area changes in a small range and the experimental data meet 3σ criteria.

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.

Effects of laser facula detector array parameters on measurement accuracy of far-field beam quality

The detector array parameters will greatly affect the measurement accuracy of beam quality at target. In this study, the relations of the parameters with encircled power ratio and the beam radius at target were further analyzed. Since the beam at target is a Gauss-like beam, the effects of detector array's spatial resolution, effective testing area, systematic dynamic range, and surface response homogeneity on measurement accuracy of beam quality were analyzed quantitatively with numerical simulation. The results show that among all influence factors, the measurement accuracy of beam radius was greatly affected by the detector's normalized size and dynamic range, but slightly by normalized resolution and surface response homogeneity. These results were successfully applied in design of detector array and achieved good effect. The experimental data and theory are well consistent.

Stable Q-Switched Yb:NaY(WO4)2 Laser with Cr4+:YAG Saturable Absorber**Supported by the National Natural Science Foundation of China under Grant No 61405171, the Natural Science Foundation of Shandong Province under Grant No ZR2012FQ014, and the Science and Technology Program of the Shandong Higher Education Institutions of China under Grant No J13LJ05.

The passively Q-switched Yb:NaY(WO4)2 (Yb:NaYW) laser is studied. By using Cr4+:YAG as the saturable absorber, a very stable pulse train is obtained. At a high pump power, the pulse to pulse timing jitter is measured to be less than 2% and the amplitude fluctuation is less than 4%. A Q-switched average output power of 2.3 W at 1029 nm is generated with a slope efficiency of 33.9%; the one-dimensional intensity distribution of the laser facula is of the Gaussian type. The output repetition rate, pulse energy, pulse width and peak power are 33.3 kHz, 70 μJ, 36 ns and 2.0 kW, respectively. The passively Q-switched process is simulated by solving the rate equations, the simulated results are in good agreement with the experimental data.

基于上三邻域连续点计数的激光光斑实时检测

基于上三邻域连续点计数的激光光斑实时检测

Process Parameters Optimization for Green Manufacturing of Laser Cladding Based on Artificial Neural Network

Laser cladding is a new developed green manufacturing process. The main process parameters include the power of laser beam, the diameter of laser facula, the scan speed and the quantity of powder supply. It’s difficulty to analyse the influence of the process factors to the product quality because the effect mechanism is quiet complicated. Model of Artificial neural network for the optimization of process parameter in laser cladding manufacturing was developed in this paper. And proper process parameters were achieved which can provide guide for the practice production.

Surface character of laser assisted wet chemical etching of YBCO high temperature superconducting film

AbstractThe laser assisted wet chemical etching technology was proposed in this study to apply in the etching of YBCO high temperature superconducting film, which was an intercrossing application involving superconducting electronics, laser technique, and chemistry. The etched surfaces and change characteristics were studied and some important experimental results were reported, including the influences of laser density, etching duration, and direction of LaAlO3 underlay on the etching characters of YBCO film under laser radiation. The main experimental results are as follows: the etching rate of YBCO film is accelerated dramatically under laser radiation and the rate is increased over time; the etching rate is relative with the laser power density; there is no strict boundary under the whole laser facula and the surface etching degree of YBCO film changes gradually; the etched surface characteristics are greatly influenced by the direction of LaAlO3 underlay. The laser assisted wet chemical etching technology of YBCO film can overcome the defect of common wet and dry ion etching technology, and probably becomes the main etching technology of YBCO film. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2672–2675, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22809

Thermal shock effect on diamond-like carbon thin films induced by pulsed-laser

When high power laser irradiates the infrared imaging system, the system will be injured or destroyed. The damage to the systems varies for different laser wavelengths. The infrared windows are generally coated with diamond-like carbon(DLC) thin films to protect itself and improve the permeation rate. When the incid ent laser's wavelength lies outside the infrared system response wave band, lase r destroys the DLC films firstly. The DLC films' damage mechanism induced by pul sed laser is studied with the 1.06μm laser. The thermal shock effect model of D LC films is proposed. The temperature and stress distributions are deduced throu gh solving the thermal conduction equation and stress-balance equation. The theo retical analysis shows that thermal stress fracture dominants in the damage mech anism. When the irradiation energy density is E0=100mJ·cm-2 , the pressu re on the surface of DLC films at about 40μm from the center of laser facula ex ceeds the rupture intensity, the film will break and peel off. The theoretical a nalysis matches the experimental results basically, and the correctness of the t hermal shock effect model is confirmed.

The comparison investigation of direct upconversion sensitization luminescence between ErYb:oxyfluoride glass and vitroceramics

This paper investigates and compares the direct upconversion sensitization luminescence of ErYb co-doped oxyfluoride glass (ErYb:FOG) and vitroceramics (ErYb:FOV) when excited by a 966-nm diode laser. It is found that there are splendid upconversion luminescence phenomena which are studied and analyzed carefully. (1) It is found that the direct sensitization upconversion luminescence L of ErYb:FOV is generally 10 times greater than that of ErYb:FOG. It is also interesting that not only blue light but also red light increases more vigorously than green light when pumping laser power increases. It results from the Er 3+–Yb 3+ ion's cluster effect. (2) For the ErYb:FOG, there is an obvious “characteristic” saturation phenomenon. That is, the F–P log–log curves of upconversion fluorescence vs. pumping laser power are basically rather good straight lines. The smaller the laser facula is, the smaller the slope of F–P log–log curves. This “characteristic” saturation phenomenon is mainly the result of strong energy diffusion among Yb 3+ ions caused by the long-range correlation. For the ErYb:FOV, because of the small and uniform micro-crystallites with a size of about 10 1 nm, the sensitization action of Yb 3+ ion to Er 3+ ion is greatly enhanced. The “typical” saturation caused by population exhaustion is also very much increased and has great effect. (3) The most interesting phenomenon is at about 474 nm of ErYb:FOG (or 476.5, 468.5 nm of ErYb:FOV) cooperative radiation upconversion fluorescence oriented from a couple state of two Yb 3+ ions' cluster! (4) Both ErYb:FOV and ErYb:FOG have a new kind of common “diffusion–transfer” upconversion mechanism, i.e., “energy diffusion” among Yb 3+ ions sequentially followed by energy transfer between Er 3+ and Yb 3+ ions. (5) The passage of cluster effect upconversion induced by couple state of two Yb 3+ ions' cluster could be described as { 2 F 7/2( Yb 3+)+ 2 F 7/2( Yb 3+)}→{ 2 F 5/2( Yb 3+)+ 2 F 5/2( Yb 3+)}→{ 2 F 5/2 2 F 5/2( Yb 3+ Yb 3+)}→{ 2 F 7/2 2 F 7/2( Yb 3+ Yb 3+)} . To the best of our knowledge, similar mechanism has not been reported up to now.