High Power YAG Laser Research Articles

Single-ring hollow-core anti-resonant fiber with a record low loss (4.3 dB/km) for high-power laser delivery at 1 µm.

We report a 7-tube single-ring hollow-core anti-resonant fiber (SR-ARF) with a record low transmission loss of 4.3 dB/km @1080 nm, which is almost half of the current lowest loss record of an SR-ARF (7.7 dB/km @750 nm). The 7-tube SR-ARF has a large core diameter of 43 µm and a wide low-loss transmission window exceeding 270 nm for the 3-dB bandwidth. Moreover, it exhibits an excellent beam quality with an M2 factor of 1.05 after 10-m-long transmission. The robust single-mode operation, ultralow loss, and wide bandwidth make the fiber an ideal candidate for short-distance Yb and Nd:YAG high-power laser delivery.

A Near 60% Efficiency Single-Slab Nd:YAG High-Power Laser With Adjustable Pulse Duration

We report a new approach to effectively improve the optical-to-optical efficiency for quasi-continuous-wave (QCW) lasers by adjusting the pump pulse duration. During our single-slab laser test, an optical-to-optical conversion efficiency of 57% and a slope conversion of 67.8% are obtained with a maximum average output power of 7.3 kW, operating at a pulse repetition rate of 160 Hz with 470- $\mu \text{s}$ pulse duration. To the best of our knowledge, this represents the highest optical-to-optical efficiency for a QCW face-pumped Nd:YAG slab laser with such high power output ever reported.

Effect of high laser output on the central bronchi and pulmonary artery.

A diode-pump Nd:YAG high-power laser (wavelength 1320nm, power 100W) is routinely used to surgically remove lung metastases. Even pulmonary lesions in central locations are resectable via this method, yet it also carries a potential risk of damaging the larger bronchi and vessels in the vicinity. Studies investigating the safety of using high-power lasers are lacking. We therefore aimed to examine the direct effects of a 100-watt laser on the bronchi and pulmonary artery at a standard working velocity. From freshly slaughtered pigs, we isolated cylindrical specimens of the trachea, the main and lobar bronchi, and the central pulmonary artery from the both lungs. These specimens were fixed consecutively in rows behind each other on a Styrofoam surface in the laboratory. The laser's handle was clamped into a hydraulic feed unit so that the laser was focused at constant distance perpendicular to the tissue and would move at 10mm/s over the specimens. The Nd:YAG Laser LIMAX® 120 functioned at a consistent power of 100W during all the experiments. The lasered specimens were examined macroscopically and histologically for tissue damage. None of the trachea or bronchial walls were perforated. Compared to the pulmonary parenchyma, we observed no vaporization effects-only minor superficial coagulation (with a mean depth of 2.1 ± 0.8mm). This finding was histologically confirmed in each specimen, which revealed mild superficial coagulation and no damage to the cartilage. In the presence of a residual peribronchial fatty tissue, the laser effect was even attenuated. The pulmonary arteries presented no lumen openings whatsoever, merely a discrete trace of coagulation. The vessel wall revealed increased vacuolization without alteration of the remaining vessel wall. In conclusion, laser resection at 100W of the central lung areas is safe with respect to airways and blood vessels and the laser output does not need to be reduced when treating these areas.

The Effect of Laser Based Synthesized Ti-Co Coating on Microstructure and Mechanical Properties of Ti6al4v Alloy

The distinctive properties of Ti-6Al-4V alloy coupled with its poor tribological properties make it a subject of numerous researches. While titanium alloys possesses vast applications and excellent properties, their low hardness and poor tribological behaviour have retarded their applications in engineering applications. In this work, the microstructures and micro - hardness values of Ti-Co intermetallics reinforced on Ti6Al4V, were investigated. Laser surface cladding technique was employed using Nd: YAG high power laser beam for the synthesis of the powders. The feedstock powders were premixed and deposited on Ti6Al4V with varying compositions at scan velocity of 1.2 m/min. Laser power of 900W and beam size of 3mm with argon shield gas flow rate of 1.2l/min were set as the operating laser parameters. Phase identification and morphological studies of the resultant coatings were carried out using scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) respectively. The coatings displayed fine microstructure and good metallurgical bonding with the substrate containing minute or no defects such as cracks and pores. The results revealed the formation of fractions of Ti2Co and TiCo3 inter - metallic phases dispersed within the coating matrix which could be responsible for the enhanced properties attained. The hardness was increased by 150% as against the substrate.

Tribocorrosion characteristics of laser deposited Ti–Ni–ZrO2 composite coatings on AISI 316 stainless steel

The tribocorrosion characteristics of laser deposited titanium–nickel–zirconia composite coatings onto AISI 316 substrates have been investigated. Feedstock powders were blended at varying compositions and deposited onto AISI 316 using Nd:YAG high power laser beam at varying scan speeds. The relationships between laser speed, structure and tribocorrosion properties of the synthesised composite coatings were studied. The corrosion and tribocorrosion behaviour of the coatings was studied in 1M H2SO4 solution using a potentiodynamic polarisation technique. The coatings displayed fine and slightly porous structures with relatively well dispersed constituent elements. The Ti–Ni coatings deposited under 0.0067m/s had the highest corrosion resistance while addition of 5% zirconia to the Ti–Ni coatings significantly improved its tribocorrosion resistance.

Saturation pulse width effect for small signal gain measurement: theoretical model and experiment

We report a new method to measure amplitude small signal gain of a chopper base Q-switched Nd:YAG laser using saturation pulse width effect of nanosecond relaxation oscillation (RO) spikes. Formation of such RO pulses is theoretically modeled and simulated by attributing a loss function to the internal Q-switch chopper and solving the standard rate equations using real practical values associated with a laboratory Q-switched cw Nd:YAG high-power laser. It is found that at a certain chopper frequency, pulse width of the simulated RO spikes is saturated and tends to a minimum value. The performance of the represented model is verified by experimental measurements through generating nanosecond RO spiked using a frequency-variable chopper inside the cavity of the laboratory Nd:YAG laser. We observed that at a certain input pump power of 180 and 290 W, when the frequency of Q-switch chopper is respectively raised up to 5.8 and 12 kHz, oscillation of single RO pulse is established. We also found that by further increasing of the chopper frequency up to 18 kHz, FWHM pulse width of the RO fundamental pulse is saturated toward \(\sim \)163 ns. Moreover, at this frequency of chopper and input pump powers of 270 and 180 W, saturated FWHM RO pulse widths of 170 and 330 ns are measured, respectively. Obtained results show good consistency between theoretical model and experimental measurements. This saturation effect, is used to obtain amplitude small signal gain of the utilized Q-switched Nd:YAG laser as 3 and 0.8 at the above input pumping levels, respectively. At the same time by using Findlay–Clay approach the small signal gain is measured to provide a quantitative comparison with the above results. From the final results we found excellent agreement between the presented method and Findlay–Clay approach.

Surface Hardening of a Vermicular Cast Iron Used for Integral Molding Valve Seat by High Power Laser

Surface hardening intergal molding valve seat of a vermicular cast Iron was done by Nd:YAG high power laser. The effect of laser parameters on microstructure, hardness and surface quality were conducted by scanning electron microscopy (SEM) ,optical microscopy (OM) and microhardness tester. The results show that The hardening layer of free defect can be obtained with suitable laser processing conditions. The shape of crescent can be observed in the laser hardening layer.The hardening layer consists of melted zone and heat-affected zone.Ledeburite, martensite and remainder austenite can be observed in the melted zone.The heat-affected zone consists of martensite and remainder austenite with retained vermicular graphite.Laser hardening layer has no-uniformity distribution of rigidity due to no-equilibrium calefaction and cooling.The defect of sunen disfigurement can be restrained by reducing heat-input in the ending zone.

Laser Ablation of Ti-Al Alloy in Vacuum and Air Environments

The time-resolved optical emission spectroscopy of Ti-Al alloy plasma produced by the Nd:YAG high-power laser pulses with wavelength of 1064nm was investigated both in air and vacuum conditions. The comparative studies gave detailed insights that the plasmas produced in air were much hotter and denser. The quantitative descriptions indeed suggested that a cascade avalanche process would be happen followed by air plasma firstly, before the laser impacting the target surface. On the other hand, the laser energy may be considerably attenuated via hotter and denser plasma, the amount of laser energy on the target surface remarkably decreased in air condition. In addition, at high-power laser irradiance levels, there was an auto regulatory area near the target surface and the plasma parameters tend to be saturated

Vibration testing based on impulse response excited by laser ablation

This paper proposes an innovative vibration testing method based on impulse response excited by laser ablation. In conventional vibration testing using an impulse hammer, high-frequency elements of over tens of kilohertz are barely present in the excitation force. A pulsed high-power YAG laser is used in this study for producing an ideal impulse force on a structural surface. Illuminating a point on a metal with the well-focused YAG laser, laser ablation is caused by generation of plasma on the metal. As a result, an ideal impulse excitation force generated by laser ablation is applied to the point on the structure. Therefore, it is possible to measure high-frequency FRFs due to the laser excitation. A water droplet overlay on the metal is used to adjust the force magnitude of laser excitation. An aluminum block that has nine natural frequencies below 40 kHz is employed as a test piece. The validity of the proposed method is verified by comparing the FRFs of the block obtained by the laser excitation, impulse hammer, and finite element analysis. Furthermore, the relationship between accuracy of FRF measurements and sensitivity of sensors is investigated.

Cutting performances with new industrial continuous wave ND:YAG high power lasers: For dismantling of former nuclear workshops, the performances of recently introduced high power continuous wave ND:YAG lasers are assessed

Dismantling is a great challenge for nuclear companies which are facing with the cleaning of former nuclear sites. Among the available cutting processes is the multi-kilowatts laser whose power is transmitted through optical fibers. Unlike other cutting processes such as the plasma arc cutting process or the oxy-cutting process, the laser process can be easily implemented by robotic equipments. The mechanised robotic arm carries a laser cutting head to perform, with remote-controlled equipments, the cutting operation. The present study deals with the performances which can be reached with high power continuous wave ND:YAG lasers. The cutting tests were carried out up to 8 kW. The laser power was delivered through a specific power supply chain: a 0.4 mm fiber was transporting the power from the laser to a first interface (coupler) then a second 0.6 mm fiber was bringing the laser power to the cutting head. This solution allowed a power delivery chain whose length could be as high as 100 + 20/50 m. Another advantage of this kind of power supply is that the first fiber can be set in a non-contaminated environment whereas the second fiber lies in the contaminated area. The cutting head used for these tests was a specific tool developed for this laser dismantling work: it is a laser cutting head cooled by pressurized air. This tool was developed with the requirement to be able to sustain a laser power of 14 kW. The pressurized air used to cool the head is also used as cutting gas. The cutting capability was about 10 mm by kW. At the power of 8 kW, austenitic steel plates of thickness 100 mm were cut. These performances were reached with the cut started on the plate's edge. If the cut started in the middle of the plate, the cutting performances were not so high: 8 kW became the power to drill and to cut plates of thickness 40 mm.

Welding phenomena and in-process monitoring in high-power YAG laser welding of aluminium alloy

Laser welding of aluminium alloys is difficult because of their low laser coupling, easy formation of welding defects, etc. and thus the establishment of in process monitoring technique is expected in various industries to obtain highly reliable laser welds. In this study, therefore, both the reflected laser beam and radiation light from die molten pool were investigated as monitoring signals during YAG laser welding of A5052 and A5182 aluminium alloy to confirm validity and usefulness of these signals for monitoring. At the same time, laser-welding phenomena were observed through a high-speed video camera to better interpret the monitored signals. Two signals were detected by utilizing photo sensors and band pass or cut-off filters coaxially against a laser beam and from the above-back direction. In this paper, experimental setup, and monitoring and observation results were presented. The correlation between monitoring signals and welding phenomena was clarified when the welding defects such as underfilling and through holes were formed.

Experimental layout for the realization of an X-ray plasma source driven by a Nd:YAG laser for biological and medical applications

In this paper, an experimental set-up for the X-ray production (≈70 eV–25 keV energy range) by a plasma, obtained focalizing a high-power Nd:YAG laser beam on a specific target, is presented. The measures of the characteristics of a custom Nd:YAG high-power laser beam (maximum of 8 J at 1064 nm, 5 ns pulse duration) and a new disposition of the target–lens system in the interaction chamber are discussed. The aim of this research is the use of the plasma resulting by the focalization of the laser beam, which will be used as a soft X-ray source or an electron source instead of the hot filament of the standard mammographic X-ray tubes.

Wear resistance of WC p/Duplex Stainless Steel metal matrix composite layers prepared by laser melt injection

Laser Melt Injection (LMI) was used to prepare metal matrix composite layers with a thickness of about 0.7 mm and approximately 10% volume fraction of WC particles in three kinds of Cast Duplex Stainless Steels (CDSSs). WC particles were injected into the molten surface layer using Nd:YAG high power laser beam. As a result the microstructure characterized by hard ceramic particles distributed in a metal matrix with the strong bonding to substrate is formed in the surface layer of the treated metal. Dry sliding wear properties of these metal matrix composites layers were measured and compared with the wear properties of the substrate and with surfaces simply remelted by the laser beam. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show excellent interfacial bonding, coupled with substantially improved tribological properties expressed through the wear resistance increase of 8 times. The amount of WC particles was sufficient to reinforce the matrix and the particles have shown a good bonding to the matrix to support the contact stress in the layer.

Experimental study on extreme ultraviolet light generation from high power laser-irradiated tin slab

An experimental system has been set up for producing extreme ultraviolet light with high conversion efficiency by employing high power YAG laser irradiated tin slab. The dependence of extreme ultraviolet light intensity and conversion efficiency on the pump energy were studied， and the saturation effect of conversion efficiency was observed. The highest conversion efficiency of 1.6% in producing 13.5nm extreme ultraviolet light with 0.27nm bandwidth was achieved at pump energy of 250mJ, which corresponds to an intensity of 1.8×1011W/cm2.

Welding Phenomena and In-Process Monitoring in High Power YAG Laser Welding of Aluminum Alloy

Welding Phenomena and In-Process Monitoring in High Power YAG Laser Welding of Aluminum Alloy

Laser-Induced Damage of Anti-Reflection Coating for Optical Guide of YAG Laser

Antireflection (AR) coating with high damage resistance for optical guides of high power YAG laser was developed. We have indicated that each single layer films must be improved AR coating with high damage threshold. An optimum deposition of the Si02 film and Ta2O5 films that compose the AR coating was studied by the Taguchi method. Reflectance and laser-induced damage threshold of AR coating was less than 0.2% and 15.9 J/cm2, respectively at 1064 nm. The AR coating irradiated by cw YAG laser of 3-kW class was durable for 5 minutes.

Periodische Modifizierung von Polymeroberflächen durch Laserinterferenzstrukturierung / A Periodic Modification of Polymer Surfaces by Laser Interference Structuring

The so-called laser interference microstructuring allows to vary material surfaces with respect to their chemistry and/or roughness so that their characteristics may be modified in a purposeful manner. The preparation of exactly periodical surface microstructures and nanostructures on polymeric materials is examined with regard to their geometry and their dimensions. Different parameters of a nanosecond pulsed Nd:YAG high-power laser are used for this purpose, e.g. the energy density introduced into the material or the number of pulses. Apart from white-light interference microscopy and AFM microscopy the horizontal microscopy is employed for an analysis of the surface features, to assess the hydrophobic nature and chemical variation of the polymer surfaces after they underwent a laser induced modification.

Application of pulse-modulated high-power YAG laser to welding of heavy plates

Application of pulse-modulated high-power YAG laser to welding of heavy plates

Quantitative Charakterisierung von laserinterferometrisch induzierten periodischen Oberflächenmikrostrukturen/ A Quantitative Characterization of Periodical Surface Microstructures Induced by Laser Interference

A specific laser interference system allows to microstructure material surfaces very fast and directly in a topographical respect, i.e. avoiding any time-consuming expensive after-treatment. Several partial beams of a Nd:YAG high-power laser which are of a large coherence length are superimposed over a substrate surface, i.e. are caused to interfere here. Under certain intensity conditions, the interference pattern form a laterally periodical modification of the surface topography of the substrate exposed to irradiation. Structural dimensions may be varied from a micron scale to a sub-micron scale. Various exposure processes and interference geometries cause a formation of different patterns. Likewise, microstructures of various aspect ratios and fill factors may be realized.

高出力ＹＡＧレーザによるＺｎめっき鋼板の重ね溶接性に及ぼすめっきの表面形態の影響

The effects of surface morphology of zinc electroplated steel sheet on high power YAG laser lap weldability were studied. In zero gap lap welding, clearance was naturally formed in uneven zinc electroplating that controlled the surface morphology, and suppression of sputtering was made possible by the clearance. It was found that the laser lap weldability was improved by the uneven zinc electroplating.