High Power Diode Laser Source Research Articles

Laser cladding of stainless-steel ball valves by a high-power diode laser source with a rectangular beam spot

In this paper, the laser cladding of Ni60 + WC powder on the stainless-steel ball valves is investigated to improve the corrosion resistance and the wear resistance of industrial ball valves. A 2-kW high-power diode laser source based on beam multiplexing is used as the processing source to clad the ball valves. To make this diode laser source more reliable for laser cladding, a homogenizing optical system is designed and optimized to transform a circular beam spot output from the optical fiber to a rectangular spot with a flat-top distribution. Employing this diode laser source, the laser cladding of the stainless-steel ball valve is successfully achieved by use of the pre-set powder feeding. The hardness testing experiments are then performed on the ball valves of different diameters, followed by the evaluation of the thickness and hardness of the cladding coating. It is experimentally demonstrated that the microhardness of the ball valves is improved by 2.7 times and the cladding layer has no cracks, which proves the superior performance of the stainless-steel ball valves by use of the proposed method.

A novel processing method based on the 3-spot diode laser source for the laser cladding of stainless-steel ball valves

In this paper, aiming to solve the problem of cracks in the laser cladding for stainless-steel ball valves, a novel method for defect-free processing is introduced. To realize this method, a 3-spot high-power diode laser source is developed. These three spots are respectively used for dynamic local preheating, laser cladding processing and dynamic local tempering. Using this high-power diode laser, a cladding processing of the stainless-steel ball valve with Ni60 + WC powder is successfully completed. Compared with the traditional processing approach, the cladded sample is free from any defects such as cracks and pores, which demonstrates the processing effect of this approach. This work provides a new method for the laser cladding of stainless-steel ball valves.

Study of the influence of the oscillation frequency on the surface hardening process of the 42CrMo4 alloy using an oscillating laser beam

A study of the surface hardening process of the 42CrMo4 steel alloy by means of an oscillating laser beam has been carried out. For this purpose, a fiber coupled high power diode laser source and a galvanometric mirror scanner have been used. The study is focused on determining the influence of the oscillation frequency parameter on the temperature, geometry, microstructure, microhardness and stress state of the treated region, as well as its relationship with the key parameters of the laser hardening process. The results confirm that the surface hardening process of the 42CrMo4 alloy by means of an oscillating laser beam is an alternative technique to the conventional laser surface hardening methods based on fixed optical guidance systems. On the other hand, the selected frequency of oscillation has a significant influence on the treated region, mainly on the temperature, and, consequently, on the geometry, microstructure and stress state of the same. The selection of a high oscillation frequency, able to maintain the material temperature above that of austenization and below that of melting, is decisive to ensure the stability and uniformity of the treatment.

An eave-like model for the welding of 304 stainless-steel tailor-welded blanks with different thicknesses

Due to its excellent corrosion resistance and machinability, stainless-steel material has been widely used in many different areas, such as nuclear power and the aircraft industry. In these applications, the stainless-steel parts often consist of tailor-welded blanks with different thicknesses. It is crucial to keep the tailor-welded blanks of high quality in order to satisfy the demanding requirements. To make the welding process of tailor-welded blanks simple and efficient, a novel welding model for the eave-like structure is proposed in this paper. Based on this model, the butt welding of tailor-welded blanks with a plate thickness combination of 2.0 mm and 1.0 mm are successfully completed by high power diode laser sources. For further inspecting the performance of the welded bead, we analyze the microstructure and evaluate the mechanical strength. The results prove that our tailor-welded blanks can satisfy the industrial requirements. This work gives an experimental guide on the welding of tailor-welded blanks with different thicknesses.

High power diode laser source with a transmission grating for two spectral beam combining

A novel laser-coupling structure is introduced, in which the same transmission grating is simultaneously employed by two spectral beams generated in identical resonant cavities. The novel structure doubles the number of coupled laser emitters and the output power. Eight 800-nm diode laser bars were coupled and combined with polarization multiplexing, achieving a continuous wavelength power of 212 W, a broad spectrum of 19.1 nm, an M2 (times diffraction limited factor) beam quality of 2.2×16.7 and a brightness of 236MW/cm2/sr.

Development and Thermal Management of kW-Class High-Power Diode Laser Source Based on the Structure of Two-Stage Combination

In this paper, we present an optical structure for two-stage beam combination to realize a high-power fiber-coupled diode laser source. In the first stage, dense spectral combination based on reflecting volume Bragg gratings is implemented for combining five diode laser blocks with a spectral separation of 1.5 nm, to a high output power submodule. In the second stage, submodules are further coaxially multiplexed by polarization beam combination and coarse spectral combination to obtain a higher output power. In the process of the beam combination, thermal effects of combining elements are also investigated. By using a temperature control, the diode laser source can steadily produce 3120-W power from an optical fiber with 105-μm core diameter and 0.2 numerical aperture. This paper demonstrates the benefits of this combination structure and the effectiveness of the temperature control.

Laser forming of glass laminate aluminium reinforced epoxy (GLARE): On the role of mechanical, physical and chemical interactions in the multi-layers material

The present work concerns the laser forming of Fiber-Metal Laminates (FMLs) by a high power diode laser source. FMLs are made of different layers of metal and composite material. The wide difference in the thermo-mechanical and physical properties of the different layers within FMLs makes them extremely problematic to be reprocessed. In particular, the economic shaping of FMLs in complex shapes is practically impossible, limiting greatly their field of application. Therefore, this manuscript explores the possibility of using laser forming to reprocess FMLs and obtain final components with precisely controlled bending radii. For this purpose, the effect of the laser operating parameters, namely laser power, scanning speed and number of passes, on the final shapes of FMLs was investigated. Secondly, further tests were also performed to obtain other complex shapes on FMLs from multiple laser scanning paths, side by side and equidistant on the substrates. An analysis of the failure of the substrates during the shaping process was also performed, with particular emphasis on deformation mechanisms, interfacial delamination and thermal alteration of the layers. The experimental results showed the good viability of laser reprocessing to shape FMLs, thus opening up new possible applications of this class of materials in aeronautical and aerospace applications.

Beam Shaping Technology for High Power Diode Laser Source

Direct diode lasers have some of the most attractive features of any laser. They are very efficient, compact, wavelength versatile, low cost, and highly reliable. However, the full utilization of direct diode lasers has yet to be realized. This is mainly due their poor output beam quality. Because of this, direct diode lasers are typically used to pump other lasers such as bulk solid-state (rod and thin disk) and fiber lasers. An improvement of the wall-plug efficiency and Power density necessary can be achieved by beam shaping and beam combination such as polarization coupling. In this paper, using the beam shaping technology realize good beam quality and high wall-plug efficiency. Base on bars rated to 60 W and 57% conversion efficiency, vertically stacked arrays (twenty bars) of such configuration are demonstrated with rated to about 1200W. The beam quality of high-power high brightness 880 nm laser diode source is improved with beam shaping. Beam parameter product of 79. 3 mm mrad ×81. 2 mm mrad, electro-optical conversion efficiency of more than 45.8% and continuous output power of 1 kW are demonstrated. This laser can be directly applied to cladding, surface hardening and other fields.

High Beam Quality and High Power Diode Laser Source

As the increasing applications of laser diodes in laser cladding and laser hardening, the single laser diode 0ptical power can not meet the actual requirements. An improvement of the power and Power densty necessary and it can be achieved by beam shaping and beam combination such as polarization coupling the polarization coupling technology is used to couple two laser beams with thin film plate polarizer In this paper two 880 nm vertical stacked arrays with an output power of l600 W was achieved After fast axils and slow axis collimated, the polarization direction of one stacked arrays is rotated 90 degree through a half wave plate, thus, the polarization directions of two laser stack are vertica1. The beams of two lasers are incident on the p1ate po1arizer, one transmits through it, and the other is reflected on it. Finally, two beams combine to one. Polarization coupling of two bars increases the power by a factor of 1.6, and the output power is 2500 W, electro optical conversion efficiency is more than 48%. The spot size is about2 mm x 2 mm. This laser can be directly applied to cladding, surface hardening and other fields.

High Power Diode Laser Source with Wavelength Coupling Technology

Laser diode has incited particular interest as photoelectric conversion efficiency, output power and lifetime for a variety of applications in industry processing. The single laser diode optical power has not satisfied for the actual requirements. It demands to couple several diode laser beams into one beam to output directly or by an optical fiber to improve the brightness, and it becomes the central issue to adopt the appropriate beam coupling technology which would offer high quality and high efficiency. In order to output high power, we utilized wavelength coupling technology to couple two laser beam of different wavelength together with beam splitter cube (BSC), the key technology and the principle of wavelength coupling is indicated and analyzed in this paper .Using 808nm and 980nm laser diode realize wavelength coupling with high output power, the efficiency more than 80% and spot size can be achieved after focusing to the beam size of 3×3mm2.

Post-deposition laser treatment of plasma sprayed titania-hydroxyapatite functionally graded coatings

The viability of a high power diode laser source as effective post-deposition treatment technique of functionally graded titania-HA coatings was checked. In particular, several laser treatments were performed on various coatings plasma-sprayed under different conditions to verify the presence of an operative window large enough for practical purposes and, subsequently, to identify the most promising settings of the laser parameters. Laser power as low as 80–100 W and focus distance as high as −4 mm were found to be the most feasible choice to improve the overall coating properties as well as to inhibit undesired secondary reactions between calcium phosphates and titania. Finally, the best set of the laser parameters were applied to a pure HA coating and to a titania-HA graded one, plasma-sprayed under the same conditions, to perform a comparative evaluation. The microstructural characterization by scanning electron microscopy, X-ray diffraction and the local mechanical investigation by Vickers micro-indentations proved that the degree of crystallinity of HA at the outermost layers of the graded coating could be improved without significantly altering the compositional and functional gradient. Furthermore, the properties of the pure HA coating, as-sprayed and laser treated, were found to be substantially less advantageous than those of the titania-HA functionally graded coating (higher microstructural defectiveness; inferior degree of crystallinity of HA at the working surface; lower Vickers hardness), thus confirming the beneficial effect of the compositional gradient.

On the interaction mechanisms between a high-power diode laser source and silver alloys: The case of aesthetic welding

Welding process is generally considered as a crucial stage in the manufacturing of decorative items in silver alloys. It is mostly hand-made by using oxy-fuel torch and the final performance of the manufactured goods is too strongly related to the capability of skilled technicians and to the settings of factors often unpredictable. Further, spreading and out-of-control oxidative phenomena, troublesome reprocessing of the welded parts and unsafe operational conditions are determining a progressively growing demand for alternative welding technologies. The matter of the present investigation is therefore to evaluate the suitability of a high-power diode laser source in automatic butt-welding of sheets in ‘800/1000’ and ‘925/1000’ silver alloys. Interaction mechanisms between laser beam and underlying silver substrates in a chemical active environment were studied. A ‘first approximation’ oxidation model and, accordingly, simple tools for monitoring and control of the welding process was then proposed. Finally, butt-welding of thin silver sheets was successfully experimented.

Development of a Surgical Diode-Laser System: Controlling the Mode of Operation

The aim of this study was to develop a microcontroller based surgical diode laser system and to test it at two different modes (continuous [CW] and modulated) in vitro on lamb liver tissue. In laser surgery, depending on the properties of laser source (wavelength, power, application time, and mode of operation), the effects observed on the tissue may change from carbonization to hyperthermia. The aim is to remove the target tissue without giving any thermal damage to the surrounding tissue. Carbonization should be avoided, thus controlling the mode of operation is very crucial. The system consisted of a microcontroller based control unit, 980-nm high-power diode laser source, and fiber delivery unit. This system has the capability of delivering different modes of laser energy to the target tissue ranging from CW to 20-Hz modulated beams. The surgical diode laser system was tested on liver tissue in vitro. Efficiency of laser-tissue interaction was quantified in terms of thermal alteration per unit energy and corresponding carbonization level. Modulated mode resulted in larger coagulated area with minimum carbonizations. Carbonized area/thermally altered area (CarbA/TAA) ratio for CW mode of operation at 16 J is 0.35; however, this ratio was found to be 0.05 at modulated mode, when even 10 times higher energy (160 J) was delivered to the target tissue. Results emphasized the significance of mode of operation as well as the other laser parameters. Modulated mode was found to be a promising regime for safer laser surgery.