Analysis of high-power disk laser welding stability based on classification of plume and spatter characteristics

Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.

High-Power Single-Spatial-Mode GaSb Tapered Laser around 2.0 μm with Very Small Lateral Beam Divergence

We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles are fabricated to optimize the output power and spatial-mode performance. The best devices exhibit single-spatial-mode operation with room-temperature output power up to 350？mW in continuous-wave mode at an emission wavelength around 2.0？μm with a very small far-field lateral divergence angle, which is beyond state of the art in terms of single-spatial-mode output power.

A new method for measuring the pulse-front distortion of arbitrary shapes in high-power ultrashort laser systems

We present a new method that can be used to calculate pulse-front distortion by measuring the spectral interference of two point-diffraction fields in their overlapped district. We demonstrate, for the first time, the measurement of the pulse-front distortion of the pulse from a complex multi-pass amplification system, which exists in almost all high-power laser systems, and obtain the irregular pulse-front distribution. The method presented does not need any reference light or assumption about the pulse-front distribution, and has an accuracy of several femtoseconds.

High-Power Passively Q-Switched Nd:YAG Laser at 1112 nm with a Cr^(4+):YAG Saturable Absorber

A high-power passively Q-switched Nd：YAG laser operating at lll2nm with Cr4＋：yAO as a saturable absorber is demonstrated. Under 808 nm diode-direct pumping, the maximum average output power of 2.73 W is achieved at the pump power of 16.65 W, corresponding to an optical-to-optical conversion efficiency of 16.4%. At the same time, the pulse width, pulse repetition rate, single pulse energy and peak power are 27.2ns, 9 kHz, 303.3#3 and 11.2kW, respectively. As far as we know, the result gives the highest average output power at 1112nm generated by an 808 nm diode-end-pumped Nd：YAG laser.

Elucidation of Metallic Plume and Spatter Characteristics Based on SVM During High-Power Disk Laser Welding

During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.

High-Power Continuous-Wave and Acousto-Optical Q-Switched Ho:(Sc_(0.5)Y_(0.5))_2SiO_5 Laser Pumped by Laser Diode

We experimentally investigate the continuous-wave(cw)and acousto-optical(AO)Q-switched performance of a diode-pumped Ho:(Sc_(0.5)Y_(0.5))_2SiO_5(Ho:SYSO)laser.A fiber-coupled laser diode at 1.91m is employed as the pump source.The cw Ho:SYSO laser produces 13.0 W output power at 2097.9 nm and 56.0%slope efficiency with respect to the absorbed pump power.In the AO Q-switched regime,at a pulse repetition frequency of 5 kHz,the Ho:SYSO laser yields 2.1 mJ pulse energy and 21 ns pulse width,resulting in a calculated peak power of 100 k W.In addition,at the maximum output level,the beam quality factor of the Q-switched Ho:SYSO laser is measured to be about 1.6.

Indoor Space Modeling and Parametric Component Construction Based on 3D Laser Point Cloud Data

In order to enhance modeling efficiency and accuracy,we utilized 3D laser point cloud data for indoor space modeling.Point cloud data was obtained with a 3D laser scanner and optimized with Autodesk Recap and Revit software to extract geometric information about the indoor environment.Furthermore,we proposed a method for constructing indoor elements based on parametric components.The research outcomes of this paper will offer new methods and tools for indoor space modeling and design.The approach of indoor space modeling based on 3D laser point cloud data and parametric component construction can enhance modeling efficiency and accuracy,providing architects,interior designers,and decorators with a better working platform and design reference.

Formation of choroidal neovascularization under macular fovea after high-power laser irradiation: a case report

Dear Editor,I am Dr.Shan-Shan Li,from Northern Jiangsu People’s Hospital,Yangzhou,China.I write to present the case of formation of choroidal neovascularization(CNV)under the fovea after high-power laser irradiation.Currently,there is an increasing availability and accessibility to laser instruments,but improper use of these tools can lead to macular damage and irreversible visual impairment.

An accurate and stable method of array element tiling for high-power laser facilities

Due to laser-induced damage, the aperture of optics is one of the main factors limiting the output capability of highpower laser facilities. Because of the general difficulty in achieving large-aperture optics, an alternative solution is to tile some small-aperture ones together. We propose an accurate, stable, and automatic method of array element tiling and verify it on a double-pass 1 × 2 tiled-grating compressor in the XG-III laser facility. The test results show the accuracy and stability of the method. This research provides an efficient way to obtain large-aperture optics for high-power laser facilities.

High-Power Dual-End-Pumped Actively Q-Switched Ho:YAG Ceramic Laser

We present a high-power Ho：YAG ceramic laser pumped at 1908nm. Using a dual-end-pumped structure, the maximum continuous-wave output power of 48 W is obtained, corresponding to a slope efficiency of 70.4% with respect to the absorbed pump power. At actively Q-switched mode, the maximum average output power of 46 W and the minimum pulse width of 21 ns are achieved at a pulse repetition frequency of 20 kHz, corresponding to a peak power of approximately 109.5kW. In addition, the beam-quality M2 factor is found to be 1.4 at the maximum output power.

High-Power Continuous-Wave Nd:GdVO4 Solid-State Laser Dual-End-Pumped at 880 nm

A high-power cw all-solid-state Nd：GdVO4 laser operating at 88Onto is reported. The laser consists of a low doped level Nd：GdV04 crystal dual-end-pumped by two high-power diode lasers and a compact negative confocM unstable-stable hybrid resonator. At an incident pump power of 820 W, a maximum cw output of 240 W at 1064nm is obtained. The optical-to-optical efficiency and Mope efficiency are 40.7% and 53.2%, respectively. The M2 factors in the unstable direction and in the stable direction are 4.38 and 5.44, respectively.

High-Power and High-Efficiency Operation of Terahertz Quantum Cascade Lasers at 3.3 THz

A high-power and high-effciency GaAs/A1GaAs-based terahertz （THz） quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758mW with a threshold current density of 120 A/cm2 and a wall-plug effciency of 0.92% at 10K and 404mW at 77K are obtained in pulsed operation. The maximum operating temperature is as high as llS K. In the cw mode, a record optical output power of 160roW with a threshold current density of 178A/cm2 and a wall-plug efficiency of 1.32% is achieved at 1OK.

Random pinhole attenuator for high-power laser beams

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical science.Laser intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption filter.These devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily damaged.In this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam properties.With this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its characteristics.In addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was preserved.Consequently,the RPA possesses significant potential for a wide range of applications.

The use of laser ranging to measure space debris

Space debris is a major problem for all the nations that are currently active in space. Adopting high-precision measuring techniques will help produce a reliable and accurate catalog for space debris and collision avoidance. Laser ranging is a kind of real-time measuring technology with high precision for space debris observation. The first space-debris laser-ranging experiment in China was performed at the Shanghai Observatory in July 2008 with a ranging precision of about 60-80 cm. The experi- mental results showed that the return signals from the targets with a range of 900 km were quite strong, with a power of 40W （2J at 20 Hz） using a 10ns pulse width laser at 532 nm wavelength. The performance of the preliminary laser ranging system and the observed results in 2008 and 2010 are also introduced.

Fundamental Architecture and Analysis of an Antimatter Ultra-Intense Laser Derived Pulsed Space Propulsion System

Antimatter has been generated in large quantities by the Lawrence Livermore National Laboratory Titan laser. The Titan laser is an ultra-intense laser system on the order of approximately 1020W/cm2 with pulse durations of roughly 1ps. With the Titan laser incident on a high atomic number target, such as gold, antimatter on the scale of 2 × 1010 positrons are generated. Roughly 90% of the generated positrons are ejected anisotropic and aft to the respective target. The mechanisms for the laser-derived positron antimatter generation involve electron interaction with the nuclei based on bremsstrahlung photons that yield electron-positron pairs as a consequence of the Bethe-Heitler process, which predominates the Trident process. Given the constraints of the current and near future technology space, a pulsed space propulsion configuration is advocated for antimatter derived space propulsion, similar in concept to pulsed radioisotope propulsion. Antimatter is generated through an ultra-intense laser on the scale of a Titan laser incident on a gold target and annihilated in a closed chamber, representative of a combustion chamber. Upon reaching a temperature threshold, the closed chamber opens, producing a pulse of thrust. The implication of the pulsed space propulsion antimatter architecture is that the energy source for the antimatter propulsion system can be decoupled from the actual spacecraft. In contrast to conventional chemical propulsion systems, which require storage of its respective propulsive chemical potential energy, the proposed antimatter propulsion architecture may have the energy source at a disparate location from the spacecraft. The ultra-intense laser could convey its laser energy over a distance to the actual spacecraft equipped with the positron antimatter pulsed space propulsion system. Hydrogen is considered as the propulsive fluid, in light of its low molecular weight. Fundamental analysis is applied to preliminarily define the performance of the positron antimatter derived pulsed space propulsion system. The fundamental performance analysis of the antimatter pulsed space propulsion system successfully reveals the architecture is viable for further evaluation.

Structured Light 3D Vision Based on Laser Scanning Space-encoding and Its Synchro Control

This paper presents the principle and mathematic model for the 3D depth map method based on space encoding images performed by modulating scanning structuredlight according to time sequences,and the synchro control among the camera,laser diode modulation and scanning polyhedron.

Fundamental Architecture and Performance Analysis of Photofission Pulsed Space Propulsion System Using Ultra-Intense Laser

Photofission enables a unique capability for the domain of non-chemical space propulsion. An ultra-intense laser enables the capacity to induce nuclear fission through the development of bre- msstrahlung photons. A fundamental architecture and performance analysis of a photofission pulsed space propulsion system through the operation of an ultra-intense laser is presented. A historical perspective of previous conceptual nuclear fission propulsion systems is addressed. These applications use neutron derived nuclear fission;however, there is inherent complexity that has precluded further development. The background of photofission is detailed. The conceptual architecture of photofission pulsed space propulsion and fundamental performance parameters are established. The implications are the energy source and ultra-intense laser can be situated far remote from the propulsion system. Advances in supporting laser technologies are anticipated to increase the potential for photofission pulsed space propulsion. The fundamental performance analysis of the photofission pulsed space propulsion system indicates the architecture is feasible for further evaluation.

Effect of the high-power electromagnetic pulses on the reactivity of the coal-water slurry in hot environment

An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated.In contrary to the previously investigated laser-induced fuel atomization that occurs at the room temperature,the pre-heated(to 400 K)slurry becomes dry enough to prevent the explosion-like steam formation.Thus,fuel does not atomize and the ignition does not accelerate.Furthermore,the absorption of several laser pulses leads to evident sintering of irradiated surface with following increase of the ignition delay time for up to 24%.Variation of the pulse energy in range 48-118 mJ(corresponding intensity up to 2.4 J·cm^-2)leads to certain variation of the increase of ignition delay.The strong pulsed overheating of the coal water slurry which does not initiate the fine atomization of the fuel generally makes its ignition longer.

Advanced Space Laser Communication Technology on CubeSats

The free space optical communication plays an important role in space-terrestrial integrated network due to its advantages including great improvement of data rate performance,low cost,security enhancement when compared with conventional radio frequency(RF) technology.Meanwhile,CubeSats become popular in low earth orbit(LEO) network because of the low cost,fast response and the possibility of constituting constellations and formations to execute missions that a single large satellite cannot do.However,it is a difficult task to build an optical communication link between the CubeSats.In this paper,the cuttingedge laser technology progress on the CubeSats is reviewed.The characters of laser link on the CubeSat and the key techniques in the laser communication terminal(LCT) design are demonstrated.

Project New Orion: Pulsed Nuclear Space Propulsion Using Photofission Activated by Ultra-Intense Laser

Project New Orion entails a pulsed nuclear space propulsion system that utilizes photofission through the implementation of an ultra-intense laser. The historical origins derive from the endeavors of Project Orion, which utilized thermonuclear devices to impart a considerable velocity increment on the respective spacecraft. The shear magnitude of Project Orion significantly detracts from the likelihood of progressive research development testing and evaluation. Project New Orion incorporates a more feasible pathway for the progressive research development testing and evaluation of the pulsed nuclear space propulsion system. Photofission through the application of an ultra-intense laser enables a much more controllable and scalable nuclear yield. The energy source for the ultra-intense laser is derived from a first stage liquid hydrogen and liquid oxygen chemical propulsion system. A portion of the thermal/kinetic energy of the rocket propulsive fluid is converted to electrical energy through a magneto-hydrodynamic generator with cryogenic propellant densification for facilitating the integral superconducting magnets. Fundamental analysis of Project New Orion demonstrates the capacity to impart a meaningful velocity increment through ultra-intense laser derived photofission on a small spacecraft.